CB Mods

This file is composed of descriptions of modifications to the Uniden CB which are in addition to the "main" ones described in the Bare manual.2001 Update: The Uniden 510 was recently redesigned.The beginning of this file describes mods for old-style Uniden 510s.Near the end, there are mods for the new style 510 as well as the Uniden 66/68 model.


Hi folks, The following are the Young and Wormus mods. They work very well.

Can anyone tell me what the Young and the Wormus modifications to the 510xl are, or point me into the right direction in the archives? Thanks Gerard"

Rife-List posting from Sept 14:

Hi to all...; I have finally finished testing of a new modification to the Uniden which replaces the audio modulation method with a direct RF modulation method.; This method offers many advantages over the former, such as an excellent square wave response from DC to 250 kHz and is still very good up to 1 MHz.; Also, the pulse width, or duty cycle, is precisely controllable. The only disadvantage is a peak output power reduction from 16 watts to4 watts, so you will probably want to set your linear amplifier switches to maximum.

The circuit is very simple (only 4 parts) and costs next to nothing ($3or less).; If you are not at all handy with a solder gun, though, you might want to seek the help of someone who is.; My web page is no completed and I have no graphics to go with this, but I will try to convey all information that is required in a concise written format.

Parts required:

; 2N3904; NPN small-signal transistor; (get one that has leads1/2" long or more)

; 1N4148 or 1N914; silicon switching diode

; 10K resistor; (or try a 3.3K if your freq. generator can't putout at least 3 volts)

; 470uF 16V; electrolytic capacitor; (you may substitute higher value and/or voltage, just be sure it fits inside the radio!)

Step 1:; Remove top and bottom covers.

Step 2:; Remove the internal speaker from the bottom cover (4screws/nuts) and cut its wires close to the circuit board.; We have no need of it and it takes up valuable space.

Step 3: Place the radio upside-down with front facing you.; For all descriptions to follow, left is YOUR left, right is YOUR right. Whenever I say "from the left/right/rear edge", I mean from the edge of the radio's metal chassis.; For clarity, I have capitalized the functional name of the component leads.; Good luck!

Step 4:; Find the 27-ohm 5% resistor (red-violet-black-gold) which is located 42mm (1 5/8") from the rear edge and 14mm (9/16") from the left edge.; It is lying flat on the board.; Cut the resistor's right-side lead as flush with the board as you can (or de solder it from the bottom), then lift the resistor up on its left lead at a 45-degree angle.

Step 5:; Find the metal RF transformer labeled L2.  It is 56mm (2 3/16") from the rear edge and 33mm (1 5/16") from the left edge.; Using your solder gun, heat the top side front-left corner of L2's shield and place bead of solder there.

Step 6:; Spread the leads of the 2N3904 so Emitter and Collector point away at 45-degree angles.; Hold the 2N3904 horizontal in your left hand with the flat side (printed side) facing up and the leads facing to the right.; Solder the Emitter lead of the 2N3904 to L2's solder bead that you just made.

Step 7:; Stretch the 2N3904 Collector lead over to the free-floating 27-ohm resistor lead and solder them together.

Step 8:; Cut both leads of the 1N4148 diode to a length of about 1/4".

Solder the Anode of the diode to the solder bead on L2 and solder the Cathode (band end) to the Base lead of the 2N3904.

Step 8:; Cut both leads of our 10K resistor (or 3.3K or whatever size you picked) to about 1/4". Solder one lead to the Base lead of the 2N3904,Solder a 6" length of 20 or 22 gauge stranded hookup wire to the other side of the 10K resistor.; If you have some, slip 2 or 3 ferrite beads over; this wire to prevent RF from feeding back into the circuit.

Step 9:; Remove the audio output transformer.; It is located 30mm (1 3/16") from the rear edge and 48mm (1 7/8") from the right edge.; It is labeled "TF-375".; I recommend using de soldering braid to do this (Radio Shack #64-2090).; You must de solder all 5 leads plus the two metal tabs that extend from the metal frame.

Step 10:; Construct a jumper wire of 18 to 22 gauge solid wire and make it 18mm (11/16") between the bends.; Again, place the radio upside- down facing you.; Insert one side of the jumper wire into the left-rear transformer hole and the other side into the middle hole of the 3 front transformer holes.; Solder the jumper wire in place.

Step 11:; Position the 470uF capacitor inside the radio where the audio transformer used to be.; Solder the positive lead of the capacitor to the jumper wire you just installed, and push the negative lead through one of the transformer holes where the metal tabs were.; Solder the negative lead to the ground foil on the bottom side.

Step 12:; Flip the radio right-side up, facing you.; Notice the 4 Philips-head screws holding the circuit board to the chassis.; Look closely at the 2 screws on the right side.; There is copper foil completely around these screws and also a gap and more foil to the rear of both screws.; Using a small flat-tip screwdriver or wood chisel, scrape away the coating on the copper foil to the rear of both screws and on both sides of the gap.; Solder a short straight jumper wire across each gap.; Do it for both screws. This modification connects the circuit common to the actual chassis, which provides better grounding for the audio generator and can prevent certain types of feedback.

Step 13:; (Optional); This is a component replacement that provides for slightly sharper square waves when modulating above 200 kHz.; Find the .01uF ceramic disc capacitor just behind the 27-ohm resistor we've been working with.; It is about 7mm diameter and labeled "103M".  De solder and replace this with a 470pF disc capacitor.; This reduces the square wave rise/fall time from 125nS to about 50nS.

Step 14:; Re-assemble the radio.; When placing the bottom cover, run the 6" piece of hookup wire through one of the holes of the speaker grill. Connect your audio/function generator to this wire and chassis ground.

That's it!; BTW, the reason for yanking the audio output transformer and installing the 470uF is to smooth out RF envelope fluctuations that were occurring below about 200 Hz.; You can now enjoy experimentation all the way from DC to over 1 MHz and I will be very interested to see what we can all discover with some of the Hulda Clark frequencies and very low frequencies!; One thing I have found is that the tube does not want to light if you use a duty cycle less than about 20%. Sure hope I didn't leave anything out here.; Feel free to forward any questions regarding this mod. I will be happy to answer them.

...Tom Young

To get the power back the collector of the output transistor needs to be run at 24 volts. This can be accomplished by either using two power supplys for the CB as I did. I got a surplus 24V supply (mine is 3.6amp but 2amp should be enough) and regulated the 24 to 12 in the CB to power the front end.

I hooked in the 24V by lifting out the front leg of the jumper described in Tom's instructions (connected to 470mf Cap) and attaching the +24 to this jumper. Note this results in the back end of the jumper being at 24v it is left unconnected to the front. ie its no longer a jumper. The 24v supply takes the place of the step up from the removed transformer.

If you have questions let me know.


The neg. goes to gnd. I used one of the attachment holes left by removing the transformer.


Ralph Hartwell wrote:

C Sounds like you really know your rf. Is it possible to build or buy a Cradio sort of designed for the R-B unit. I mean one that would have no Cfilters, be designed for square waves, possibly a built in amp? Maybe a kit?

To put information on the carrier wave, you modulate it in some way. In the case of the Rife system, we simply turn the carrier wave ON and OFF. It's either there ir it's not; no in between. Speech on the other hand, is a continuously varying signal, so the modulator has to handle any value from 0 to 100%, and everything in between.

Modulators designed for speech, especially those in narrow band radios, such as the CB service, tend to be unhappy with square waves when you try to force them through the modulator. A square wave is the best waveshape if you want to simply turn the carrier on and off in the minimum time. However, square waves contain many high order harmonics.

The CB modulator does not like these high frequency components of the square wave, so it tries to ignore them. This rounds off the leading and trailing edges of the square wave, distorting your nice square wave. If you raise the frequency of the square wave high enough, eventually the modulator will turn your square wave into something approaching a sine wave. This is not what we want to drive the Rife tube with.

To some degree we can counteract this effect by seriously over driving the modulator stage bu simply increasing the signal we feed to the microphone input connections. The modulator will saturate on this increased signal, "clipping" the top of the waveform (which was square anyway). The increased input signal will effectively increase the amount of the higher order harmonics contained in the square wave - they were below the saturation point of the modulator originally - and boost their amplitude. The result is the over driven modulator will produce a somewhat better square wave. However, other inherent limitations in the radio, such as the audio modulator transformer, component values, etc, will still limit the upper frequency range you can achieve with the CB radio.

To do better, we need some type of modulation system which bypasses these limits, such as low level drive modulation. Normally, low level modulation is very inefficient, but in the case of what is basically a digital system (on and off only, as we are doing here) the efficiency can be quite high - better, in fact, then the modified CB radio can achieve.


Hi Brian

The high-bandwidth modification of the Uniden Pro510XL is capable of passing all of Dr Clarks frequencies.

I have modified a Uniden and a scope shows it is working. Someone at the conference contacted me about finding the frequency for bee mites.

I am thinking of doing some work in this area.

A drawing of piggy backing two transistors to boost the peak output voltage to 5 volts is attached and it works well. Tom puts in a separate 24 volts in another post, so you can take your pick!



{read entire section, which includes 3 of Jim's posts, before making mods. By the third post, he knows the correct components to use.}

Hi everyone,

About a week ago I was looking over my RF Parts Catalog, wherein they have some specs on a few of the final output power transistors used in CB radios. I found that the 2SC1969 and the 2SC2075 {this is incorrect - see next post for corrections} offered some potential to possibly increase the amount of modulated power from the Uniden . The transistors came in late this week and I have been running the 2075 as a direct replacement for the past few days.

Without peaking the system - just replacing the transistors, I found that the 1969 was down on power some over the stock configuration, but that the 2075 was very close to the original specs.

Tom Young gave me the places on the Uniden that I should modify to optimize the power potential of the replacement transistors. The modification I found that worked with the 2075 transistor was to turn the ferrite core of coil L6 counter clockwise ( so that the core backs out of the coil) . The difference in modulated power from resetting this coil has been enormous. L6 is located directly in front of the output transistor. I would highly suggest adding an additional heat sink to the back side of the transistor. Do this by drilling out the ID plate rivets and then attach the heat sink to the transitor mounting screw. Don't forget to use heat sink paste to couple the new transistor and the heat sink to the chassis.

Here are a few power settings - My set up was the Uniden 510XL CB driven into a 949E antenna tuner with an external 912 balun. I used a small tube, but you can use a large tube if you move the clamps very close together.

Stock 2075

no modulation 3.8 watts 5.1 watts

1000Hz 6.2 watts 12 watts

9999 Hz 11 watts 18 watts

Installed the linear to the system and found that there was no difference in peak power levels. Where the difference showed up was at the frequencies from about 2500 Hz down. Power was up from about 20 to 35 watts at all frequencies. Maximum power was reached sooner - peaking at 4000 Hz and staying very level to 9999 hz. The SWR as before tended to fall with increasing audio frequency.

The difference in the wave's intensity at lower frequency settings was quite noticable. Especially in the 400 to 1000 hz range.

I set the power levels using a 1000 hz tone, watching the forward power meter on the antenna tuner. I then switched to a 9999 hz tone and peaked the system. I took the power level up to maximum and then backed off L6 just slightly and took about 1/2 watt off the peak power to avoid fully driving the 2075 transistor.

Still to be determined are the effects on the linear - will it survive? Also need to do some tests to see if I am clipping or distorting the wave in some manner.

If you want to try this modification - be aware that it is not fully tested out yet and you may destroy your linear amp. If it works, the frequencies between 1600 and 400 that are used for infections should be a lot more efficacious.

I intend to try out the 1969 transistor this weekend in another CB. Will post results on this. The transistors are only about 2.50 each from RF Parts, but they have a 25 dollar minimum order. Expect to pay around 7 to 10 dollars for these at a retail outlet.

My thanks to Tom Young for all the help!


Earlier today I posted a modification made to the Uniden 510XL where I replaced the output transistor. In the posting I stated that I was using a 2SC2075 - this is incorrect. I had installed the 2SC1969 transistor. Everywhere in the post that I mention the 2075 you should substitute the 1969.

Installed the 2075 into another CB just a few minutes ago- results were dissappointing. Power was only up 1.5 watts with L6 peaked, and there was but a slight increase in power at lower frequencies when used with the linear amp.

If you decide to try this modification please use the 2SC1969 transistor.

Ran unit for 45 minutes straight this afternoon with no problems. What concerns me is the rather high unmodulated power levels from the CB. This needs to be reduced slightly. The power is enough to destroy some of the transmit/recieve components especially the switching transistor. It may be high enough to destroy the finals.

Can say the wave is dramatically enhanced with the 2SC1969 installed, the volume of sound from the tube is enough to make you look for a volume control to turn it down.


More info on the Uniden transistor modification. I took the radio over to my local shop, where I was informed the unmodulated power was too high and would cause failure of most linear amps.

The unmodulated power level of the CB was brought back to just under 4 watts by installing a 220 ohm 1/2 watt resistor.

To correct the unmodulated power level, one must remove inductor L8. Inductor L8 is marked on the PC board and is located directly in front of the final output transistor. L8 is nothing more than a 1/8th watt 15 ohm resistor with a small ferrite bead on one lead.

Remove L8 and then remove the ferrite bead, putting the bead on the new 1/2 watt 220 ohm resistor . Make sure the bead is located back to the same hole in the PC board it came from.

My tech tells me the linear should now be OK, but I need to run the CB a few more hours to make sure that all the parts will hold up.

The CB used to swing from 4 watts unmodulated to 19 watts fully modulated on my techs meter. Now with the 2SC1969 transistor and the 220 resistor, it swings from 4 watts unmodulated to 33 watts fully modulated. My tech showed me a CB that will go from 4 to 60 watts and he says that even with this much modulation, the CB would not damage a linear.



If you want to replace the cable between your audio frequency generator and your CB with something else, so you don't have to hold the microphone, or use a twisttie (or something) to hold the microphone on, then get a connector (of the type to plug into the CB), some coax cable (I used RG8X because I had some handy), and the type of connector that you'd need for your audio frequency generator (I used two spade connectors).

The CB connector that I have has 4 'pins', and the are numbered (on the connector) 1 through 4. I bought this connector at a local electronics store, but I think Radio Shack sells these.

Connect the braid from the coax cable to pins 1 and 3 on the connector. Connect the center wire from the coax cable to pin 2 on the connector. Pin 4 is not used for our purposes.

My frequency generator is a Ramsey, and it has two output banana plug jacks, one black, the other red.

On the other end of the coax cable, connect the center wire to the spade connector that will be connected to the red jack on the Ramsey. Connect the braid to the spade connector that will be connected to the black jack on the Ramsey.

Using this cable means that when the CB is on, the Bare-Rife device is on.


CB Handset Replacement

To replace entire handset from Uniden CB, get exact CB mike 4 pin connector replacement, available at Radio Shack, plus 18-22 ga twisted pair _shielded_ (18" or so, see below), a DPDT switch, a female BNC mount, a small metal project box, and if needed, BNC cables.

Drill hole in top of box for switch, hole in one side for BNC mount, and hole in other side for twisted pair. I got a 3A DPDT (without a center position) that came with a small plate with ON and OFF notation.

A BNC-ended cable will be needed between BNC connector on function generator and this box. I use 18", then made my switchbox-to-CB twisted pair wire 18" long. This allows me to easily connect components without stretching or bending wires in small radius, and to mount the switch wherever I want, but I have a large rack so most setups can allow it smaller. If CB and function generator are close together, perhaps 2 9" lengths could be used.

The BNC female mount is not really necessary since the BNC cable can be run directly into the box for mounting on the switch, and this may result in better fidelity. I wanted the flexibility of being able to use different sizes of BNC cables to see if had an effect on SWR. Plus, the BNC mount grounds the box, making it a shield somewhat, which may result in better SWR and fidelity unless the box were grounded otherwise.

On one side, the ground shields are switched to the red wire. On the other, the signal from the function generator is switched to the yellow wire. A DPST switch could be used, but they are not as common. The black wire is not used.

DPDT Switch ( )

To red wire in handset ( ) To yellow wire in hand set

To shield wire of handset and BNC ( ) To center conductor of BNC shield.

The pinout of the connector, as viewed from the front (F) face:

Yel Red


Shd Blk U

U is indentation on connector. Shd is shield. Blk not used.

Adding the DPDT switch to the circuit is not really necessary. A plain cable, with the connections already made in the connector works fine, and with better fidelity. In this case, though, the CB ON-OFF knob is used to turn the system on. If there is a lot of start-stop testing, to save a bit of wear by not having to turn the CB on and off constantly, it is beneficial to have the switching box.


Better than the scheme with the switch box to replace the handset and cord is to use an RG59 (or other appropriate) cable and make a CB mike jack connector to BNC (or whatever connector is on the freq generator.) Wire the connectors as if the switch is always on. Then, use the power switch on the CB to turn the signal on and off.

This would be to connect the shield of the coax to the red and shield positions of the mike connector, and the center conductor of the coax to the yellow position. Twisted shielded pair could also be used.


On 13-Nov-97, Kb46321@aol.com wrote: >Mr. Wormus,

>"I am now using a Uniden 510XL modified per Tom Youngs Instructions >(very >easy). I am running the output stage at 24V so that ther is no power >loss and it really gives nice clean SQ-waves at all freqs."

>I have Tom's instructions for modifying the 510, but I am unaware of a >way of >getting the power back up. How do you do it?

>Thanks, >William Beiriger

To get the power back the collector of the aotput transisto needs to be run at 24 volts. This can be accompolished by either using two power supply for the CB or as I did. I got a surplus 24V Supply (mine is 3.6amp but 2amp should be enough) and regulated the 24 to 12 in the CB to power the front end.

I hooked in the 24V by lifting out the front leg of the jumper described in Tom's instructions (connected to 470mf Cap) and attaching the +24 to this jumper. Note this results in the back end of the jumper being at 24v it is left unconnected to the front. ie its no longer a jumper. The 24v supply thkes the place of the step up from the removed transformer.

If you have questions let me know.


The neg. goes to gnd. I used one of the attachment holes left by removing the transformer."


Hi Folks,

If you do the Tom Young and Ron Wormus mods you should keep in mind the following: The 470 microfarad capacitor that Tom specifies at 16 volts should be raised to 24 volt or higher. The signal generator output level is much higher than the original CB mod calls for. You will need 3 to 8 volts peak to switch on the transistor. If you have a means of adjusting the 24 volt power supply to say between 12 and 24 volts you could set your linear on Hi and adjust your power to the tube that way.

Best regards, William Beiriger


I finally got my Tom Young modified CB working. Had to use a 3.9K resistor vs the 10K Tom recommends.

At 10K hz the unit gave me 50 watts of power with my linear. I peaked out coil L7 and then coil L9. Heat the slug to melt the wax and then turn the slug counter clockwise. After peaking, the power went up to 70 watts. Will be getting in some more 2SC1969 transistors by either end of week or early next week to try with Tom's mods. After that will add on the 24 volt power. Will let everyone know how it works.



Subj: 6 more watts

I have replaced out 10 resistors in and around the resonant circuits in the Uniden. I managed to find a total of 6 more watts of power from changing out two of the resistors to a 1/2 watt from the 1/8th watt.

Just in front of coil L-10 ( marked on the pcboard) where it connects into the pc board are 100 ohm and 180 ohm resistors. Replacing these two with 1/2 watt versions of the same ohms gave me 6 watts more power from the CB. All the other resistors did nothing to the power levels.

100 Ohm brown Black brown

180 Ohm Brown Gray Brown



> My question concerns the 24volt mod..... instead of obtaining a new wire or > set of wires to carry the 24 volts to the output transistor of the CB and > having to drill another hole for it, why not simply unsolder the existing > 12volt hookup leads from their place on the board and use these?

The 12 volt wiring must be left intact to feed all the radio's circuitry except for the output transistor, which is fed by the 24-volt supply.

> I am also wondering why the application of the 24volts to the CB circuitry > doesn't blow up (overvoltage) other parts of the CB (since they are desinged > for 12volts) like the RF occilator circuit (and just exactly how does it get > its power in this setup?).

If you fed the 24 volts to the entire radio, it most assuredly would blow much of the circuitry, which, just as you say, is designed for 12-volts operation only. The 24 volts can ONLY be fed to the collector of the 2SC2166 RF output transistor, which is designed to handle this kind of voltage.


You can run the CB for a good 20 to 30 minutes at 1.8 volts [to get good square waves below 300Hz and above 12KHz. ] Problem is not the voltage, it is the heat generated by the voltage that kills the CB.


A recent addition to James Bare's CB mods to the Uniden is to replace a cap which, he reports, slightly lengthens the square wave pulse, allowing full modulation, which may increase th wave's activity as much as 20%.

There is a .47uF capacitor rearward of D14, with a small "+" just in front of it. Replace this with a .68uF 50V electrolytic. The striped side faces rearward.


Reid sent me his Uniden PC 66 XL to check out. Seems that there is a lot that can be done to it to make it work better. Final configuration gives about 35 watts at 10K audio modulation.

Here is what to do to modify- all components are marked on the pc board.

1. cut D9 - found near the front of the chassis by the on- off control this is the major key modification.

2. remove tuning slug in coil L 10 found at the back of the chassis by the output transitor.

3. Replace resistor R40 (1/8th watt- red, red, black 22ohms ) with a 220 to 270 ohm 1/2 watt resistor. 220 and 270 ohm resistors are available at Radio shack for about 50 cents.. Failing to do this after cutting D9 will overdrive the linear amp and burn it out.

4. Spread the end coils of L8 about 1/16" each. L8 found at the back of the chassis by the output connector. | ||||| | looks kind of like this when done.

5. Cut resistor R38 ( 1000 ohms 1/2 watt Brown, black, red ) . R38 is located just in front of the output fitting.

Replacing the output transistor with a 2SC1969 should get you over 40 watts of power.

Have fun!



I have been test running the CB (Uniden PC 66 XL). Found that about 15 min, the power transistor will badly overheat and power drops off radically. The top or back cover will have to be opened up and forced air cooling over the transistor will be required. Unlike the 510XL, the power transistor is not attached to the chassis . The heat sink on the PC66XL is an internal piece of aluminum that will not suffice for our demands.

Other than that seems to work OK. Idles unmodulated at 70 watts and then swings to a bit over 125 watts with my linear. The 510XL will probably be more reliable.



> I followed your modification steps for the Uniden 510 very carefully, double > checking all connections and subistitutions, yet there is no RF output from > the CB. Your troubleshooting hint No.2 states that I should test to make sure > that 12v is getting to the collector of the Rf transistor. Which lead is the > collector? I was getting 12v on the center pin but not on either of the > others.

This is correct --- the center pin is the collector and the other two should read zero or close to it. So, you are getting proper collector voltage to the final.

> Also, how do I test for the function of the 2n3904 transistor? I am getting > signal to the base lead but not at either of the other leads.

The collector lead (going to the 27-ohm resistor) should read about +2.4 VDC in transmit when modulating. If there is no drive from the generator, the reading will be about +5.9 VDC on your DMM. If you read +5.9, I would suggest substituting the generator with a 9V battery, with the positive to the 10K base resistor and the negative to circuit common. This should give a steady RF carrier output. If the battery test passes, it means your generator is not driving hard enough, and that maybe you didn't remove the voltage reducer --- several people forgot to do this! :-)

> One more question. You say that a higher value for the capacitor is > acceptable as long as it fits..... is 1000mf @ 35wv ok (it still fits)?

Will work great.



> << and that maybe you didn't remove the voltage reducer --- several people > forgot to do this! :-) >> > > Thanks for the reply..... I do not recall the mention of a voltage reducer in > your basic (non 24v mod) instructions. What is it and how is it removed?

Sorry for any confusion. I was speaking of the voltage reducer that many people install on the Kinnaman generator to knock it down to 240mV for the usual Rife/Bare configuration. If left connected, the 240mV square wave will NEVER activate the 2N3904 transistor --- so the reducer MUST be taken out.




G>Greetings. I'm noting the appearance of a conflict; that no CB Radio is G>capable of producing a square wave, that any basic engineer knows this as G>a basic elemental fact and that those who use a CB Radio in the G>development of a plasma device are only hobbyests. This thread is to

This is true - the CB as designed will not reproduce a square wave with any sort of fidelity due to the inherently limited audio bandwidth of the modulator circuitry. That is, it won't, when it is operated in accordance to good engineering practice.

However, in Rife/Bare service, the audio stages are severely over driven well past the point of clipping, causing the modulator output to go to saturation very rapidly due to the excessive audio signal. This causes the modulator to behave more as a switch then a linear amplifier. This tends to provide a surprisingly clean square wave modulation waveform to the final RF stage, at all but the lowest audio frequencies. In some cases, the bias is changed, resulting in the modulator operating closer to Class C than Class AB or B. Several researchers web sites contain oscillograms of the resultant RF output.

Other researchers, including myself, have taken a more digital approach to the modulation system. Note that doing so assumes that the use of square waves is the proper way to go with the Rife/Bare system. The jury is still out on that, at least in my mind.

For a review of my research, please see my web site, located at


From my site, you may also enter the Rife Biomedical Research Web Ring, which links some Rife related sites, where you will be able to obtain additional information on Rife and Rife/Bare.

( An aside here - if any of you have sites you would like to link to the Rife Biomedical Research Web Ring, please go to my web site and click on the Rife Web Ring link, and follow the instructions for entering your site in the ring. )

Not all folks involved in this research are hobbyists. There are several doctors working with this system, most, if not all of them, using modified CB's as the rf source.

G>flush out some detail if available regarding this element because I G>to produce a device with an engineer I'm acquainted with, try to do G>experiments and make reports to the Rife list. Should we use a CB

Great!! Please do post your findings, however they turn out. We're all searching for the most effective system.

G>or something else to produce a true square wave radio signal? And if G>have additional construction ideas, I'd love to hear them and I'm G>to hurry because of a lady with lung and bone cancer who may benefit G>this device.

My advice, and I'm sure it will be echoed by many others on this list, is to get a copy of Dr. Bare's manual, read it, and build a CB based system according to his plans. Don't change anything until you try it. The thing is, his system, though it may be looked down upon by professional engineers, has one great, overriding point in its favor: it works.

However, don't let me discourage you from trying something different. When you look at my web site, you'll see that I went in a different direction than Dr. Bare. I am doing it mainly for basic research, but if I had a life in the balance, I would opt for Dr. Bare's unit in a heartbeat.

Ralph W5JGV


As some of you are aware I burnt out some of the components in my 24 volt power supply used for my Tom Young modified CB. I had to special order in the 200 ohm pot that was fried. The problem was replacing the 59014 transistor. This is an odd ball. In desperation I put a radio shack 2N4401 transistor in it's place and it worked perfectly.

Tom says that we could use up to a 28 volt power supply, so I checked the output of the transformer into the rectifier circuits which was 26.8 volts. I then set my voltage output to 25.8 volts and the CB picked up a bit by doing so.

So far so good.



> << After powering up and tuning L6 and L9, .... >> > > > Where approximately did you get the best tune, all the way in or almost all > the way out?

About 3mm from the top on both coils. Somewhere around 11 watts peak.


You are right! There was a button and I did have it on average. When I put it on peak, and tune L6 and L9, I get a little over 11 watts (should be 20-22 according to Tom's instructions) and the power didn't vary with modulation frequency.

Also, I put ferrite beads (0-40mhz) on the hot 24v power lead and that cleaned up the wave form a bit, although there is a small portion at the beginning of the pulse (top and bottom) that is higher than the rest. I'm still getting about 1 v p-p of pulse waveform at the 24v power supply terminal.

My biggest concern is that I'm not getting 20-22 watts (peak) and the heat seems too much. The RF output transistor runs very hot and so does L6. Any suggestions?


Now that you have the tuner power meter switch in the average position, where the power does not change with modulating frequency, try to understand that if the modulating frequency is gating the RF at a 50% duty cycle. 50% of the time the RF is off and when the RF is on, assume the output power is 22 watts, the average power is 1/2 of 22 or 11 watts.

With respect to using ferrite beads on the hot 24V power lead, that should not be necessary. The 1V p-p of the modulating wave form should not be present at the 24V power supply terminals. This should be an electronically voltage regulated power supply. It would appear that either the supply is not regulated, the regulator is not working, or the supply is under rated for the load requirements. I believe that the actual current to the CB is about 1 amp, but I have not made the modification nor measured the current.

Domenic --------------------------------------

> I am having a problem with the 24v mod. The 2SC2166 is getting very > hot and L6 got so hot it melted the rest of the wax. Ron suggested a heat > sink on the 2166 but I don't see where it would go and anyway L6 shouldn't > be getting that hot (I don't think) Could I have something wired wrong?

L6 does not carry any DC, it is just part of the RF output network leading from the collector of the 2SC2166 to the antenna. My guess is that your L6 coil is not creating its own heat, its just getting hot by thermal conduction because it's soldered only a fraction of an inch from the 2SC2166 collector, and you said the transistor is getting very hot. The 2SC2166 definitely requires a heat sink with the 24V mod. An excellent heat sink to use is Radio Shack #276-1368 for 1.49. Simply drill out the 2 pop rivets on the rear name plate and remove it. Use the supplied 4-40 screw to mount the sink in place of the transistor's existing hardware. And don't forget to use heat sink compound (RS #276-1372 for 1.99). You'll also have to trim off about 2 inches from the lip of one of the chassis covers. Use a hack saw or just bend it out of the way.

Good luck with it.



I have just uploaded high-res pictures of my Uniden Modification to my web page. Please visit at http://members.esslink.com/~tyoung/ and let me know what you think.


>>Would like to know the purpose of D7 which is a 1N4003 as far as >>I can make out. > >The combination of the audio power amplifier (U4 TDA1905) and the modulation >transformer (T1) come up short on the peak-to-peak voltage swing required to >achieve 100% modulation under normal circumstances. Adding diode (D7) in series >with the voltage supply to the transmitter RF stages that are to be modulated >reduces the supply voltage by about one volt which in turn compensates for the >shortfall in available modulation voltage and results in the maximum achievable >modulation being closer to 100%. > >Domenic > Hi Domenic and all interested,

After my original posting I went back to check the transistors. Picked up the NTE236 and found the insulating bush still attached!!! So that was the reason I made smoke eh!! Released the 2SC1969 to fit the bush and found it was too big for the stud fixing hole. The two transistors may be electrically similar or equivalent but mechanically they are not. However from my box of *removed parts* I found the original bush from the 2166 first removed, many weeks ago, in the upgrade. Fitted this and checked D7 which had a greaty reduced back to front ratio. Fired up and the system still worked. Assume that as the collector of the output stage, D7 and the modulation transformer share a common path all three of these components could be at fault from the self imposed surge!!!

Have since replaced D7 with no significant difference in perfomance. Awaiting the arrival of two 2SC1969's hopefully today.



I made the CB mods as suggested on Tom Young site.

Instead of using another power supply to get the 24V, i used the 20-22VDC made by my ASTRON RS-35A just across the big blue capacitor.

I only need one wire from the "+" of this cap. to my uniden CB because the "-" is shared by the same power supply. The wire is passing through one of the holes near the big transformer of the ASTRON p/w supply, and on one side of the CB just where we can put a little metal base.

I put one ferrite on this wire inside the CB and one other ferrite inside the ASTRON to make sure RF is not passing.

I also put a heat sink just behind the RF transistor output (outside the CB).

Well, all done and i get between 15 and 20 Watts of output, is this nice?!.


I was modifying a new Uniden 510 XL and found a component short. It is possible that this short may be a common malady with all new Unidens.

There is a brown disc capacitor located on the solder side of the pc board. Old Unidens have very short leads on this cap. My new Uniden had one short lead and one long lead, the long lead was not only touching a solder joint it shouldn't, it was also soldered down in two places. Some checking about with other Uniden's I have, showed that only the very tip ends of wire leads on the brown cap should be soldered. The tip end was soldered to the correct tracing on the board. So if you have a relatively new 510, you might check for this fault.

Make sure long bare wire lead is not touching any other solder joint!



>From cmrci@idcomm.com Sat Sep 19 16:04:13 1998

Background: In the summer, I built a Rife/Bare machine using the 510xl Pro Uniden. I decided to perform the Tom Young modifications because I needed precise control over the duty cycle and wanted a nice, clean square wave from 0-10khz (actually goes to 250khz).

I am very experienced at electronics but the whole project took me over a month to build. The CB radio was the most labor intensive part of the project (see the link to Tom Young's web page just below for the procedure). http://members.esslink.com/~tyoung/

A chiropractor I know mentioned that he would like a Rife/Bare device but didn't feel comfortable building one. It occurred to me that if the CB portion of the project was pre-made and available to be purchased, Rife technology would become more available to more people (without the brain damage of building it). I talked to my son and his friend (both high school juniors) about modifying the CBs and selling them. I helped them construct the first one (after mine) and now they have built a total of three.

The CB performs superbly. It hooks up to any function generator via a built-in female BNC connector (mounted directly on the Uniden). It derives 24 volts on the output transistor by an additional 12v power supply in series with the primary 12v power supply. Because of the 24 volts on the output transistor, it drives the linear at a full 225 watts (0-10,000 hz.) It has a built in cooling fan that blows directly on the power transistor. For maximum convenience, it has a terminal strip that provides 12volts for powering three devices like fans and antenna tuner illumination. They are going to sell these first three for $250 each and include a 1 year warrantee. Subsequent units will sell for $300. A feature list follows.

Features: High performance Uniden 510xl CB Radio

Use as CB for new Bare/Rife system or as significant upgrade for existing Bare/Rife system

CB connects directly to any function generator via built-in female BNC connector

Excellent square wave response from DC to 250KHz

Precisely controllable duty cycle (with variable duty cycle function generator)

Tom Young direct modulation method (with BNC mounted on CB)

Included additional 12 volt power supply for a total of 24 volts on output transistor for 225 watts of power (0-10,000 hz)

Built in cooling fan for CB output transistor

Two terminals hook to any 13.8 volt power supply

Built in terminal block for powering three devices (fan, antenna tuner illumination, etc...)

1 year warrantee

$250 each - Introductory price for first three (goes up to $300 thereafter)

$50 flat fee for repairs after 1 year warrantee expires

Contact: Mark Robbins (303) 741-4566 cmrci@idcomm.com My plasma tube and transmission line: The tube fires (and looks) better than my wildest dreams. It fires every time at any frequency with very low SWRs. The credit goes to Ralph Hartwell for his balun-less transmission line and also his trigger coil. As far as I know, I am the only person to combine both technologies into the same system. For information on both technologies, see Ralph's web page at: http://home.att.net/~ralph.hartwell/index.htm

The tube itself is a 22" long 100% argon bubble tube by Robert Randazzo at absolutely Neon. His web site is at: http://www.kalamark.com/neon/

A entrepreneurial opportunity exists here (and a chance to make Rife Technology even more available): No one around here is particularly handy with mechanical construction. If there is someone out there that would be willing to manufacture and sell the wrapped tube and tube holder to Rife system builders, I would be happy to turn loose the construction plans. The combination of this CB and a pre-assembled holder/tube/transmission line makes building a Rife system a snap (literally plug and play). This would put machines in more people's hands.


> One question pops into mind when I read about the 24V CB mod. It > may have been answered before and I missed it. Wouldn't a > more powerful amp allow the same kind of performance? I realize > it would not be able to go to 250Khz, only 35KHz, but other than > this, what is the purpose? Does it make squarer waves?

A more powerful amp would increase the cost significantly whereas an additional 12v power supply is relatively lower cost. The squarer waves come from Tom Young's original modification where he turns the carrier on and off directly with a transistor vs. trying to AM modulate through the microphone input. Because Tom's direct modulation method produces less power than the AM method, the additional 12volts make up for that (very nicely).



I have a couple of Uniden PRO 510XL CB's that I am preparing for use in Rife/Bare devices.

The two Unidens have slightly different PCB layouts, with different identifying numbers on them: - one has main board PCB "PA-375AA" and daughter board PCB "PA-389AB" - other has main board PCB "PA-375AB" and daughter board PCB "PA-389AC"

The components, listed in Dr. Bare's book, for modification, are located in the same places in both CBs.

Various other components are not in the same places in both CBs.

A recent email by Dr. Bare, concerning the brown disc capacitor on the back of the PCB, is what caused me to notice the differences. (I was checking to see if my CBs had the problem that he mentioned, when I noticed that the capacitors are located in slightly different positions in the two CBs).

Might different PCB layouts have an effect on the outcome of the modifications?

If so, this might explain why some people's Rife/Bare devices are more effective than other people's devices.



I just checked my CB's, my old ones were the 375AA and 389AB, the one new one I have is the 375AB and 389AC. Both units work well. The only difference that I am aware of is that the new pcboard allows the CB to make more power when it is modified,even without the final transistor replacement. I was wondering why the last two units I modified gave over 20 watts when finished. The last one was 22.5 watts.

That cap is located in a slighly different position, but it is on the same tracing.



> > How much are your modified CBs? I take it these have your > > mod which removes the audio section.

> Yes, both of my mods remove the audio output transformer and directly > modulate the RF pre-driver stage. My new Version 2 mod employs adjustable > gating from about 0.7 to 23 Hz and also has adjustable RF carrier control > during gating. > > Currently, I'm selling the Version 1 Uniden for $120 and the new Version 2 > model > for $190. Both include the 24V/2A supply that's needed for 20 watts > output. If > you already have a 24V supply, simply deduct $45. > > Best regards. > Tom (tyoung@esslink.com)


To all those on the Rife-List,who are interested in a schematic of the "Uniden 510 XL" This is the radio that Jim Bare uses in his setup. This schematic is an up to date version, and is 18"x 24" in size with all parts values and designations listed in very clear and readable black and white print.

This is a schematic only. If anyone is interested in obtaining one I will ship you an 18x24 schematic rolled in a mailing tube via priority mail for a donation of $8.50 to cover all the costs involved in the shipping and handling. This cost is for shipping within the U.S.A only. For Canada or other countries contact me via "ground mail" or the e-mail address bio-genesis@juno.com

PLEASE DO NOT respond to me via the "rife-list" regarding this item.

Send a check or money order payable to; or write to; R.Harrison 603 Brenda Dr. Brandon Fl. 33510

This will be shipped in a large mailing tube.

I will need your exact mailing address and zip code.


> Could someone explain the functional operation of the CB? I know this is the > most basic of questions, but here we have it; I assume the carrier frequency > is present when the audio is not modulating it.

A CB radio is a fairly simple Amplitude Modulated (AM) radio system, consisting of a transmitter and a receiver. Of course, in Rife/Bare work, we only use the transmitter, so that's what my comments will refer to in this discussion.

The only purpose of the CB transmitter is to generate a modulated radio frequency signal which is used to light the Rife/Bare tube.

To do this, it uses a carefully controlled oscillator, which has its output boosted by several amplifier stages until it reaches a power level of 10 watts or more. This amplified signal is called the RF carrier wave; so called because it "carries" the modulation on itself.

A series of audio amplifier stages, called the Modulator, take the signal from the signal generator (or microphone) and amplify the audio signal to a power level of about 5 watts. The audio and carrier signals are combined in the Final Radio Frequency Amplifier stage, to produce an Amplitude Modulated RF signal.

With no modulation, the CB transmitter will put out a steady Continuous Wave (CW) carrier signal. This carrier wave continuously oscillates from positive to negative and back again at the carrier frequency rate, which is 27,120000 Hertz, or 27.12 mHz every second. If you listen to this unmodulated CW signal on a receiver, you would hear only silence, a there is no modulation being applied to the carrier.

Applying this signal to a Rife/Bare tube will simply light the tube, and, depending on the arrangement of the feed wires, balun, etc., some of the RF energy will be radiated from the tube and wires connected to the tube.

> Now the square wave which is > oscillating equally above and below ground enters the picture...the carrier is > amplitude modulated to conform to the square wave envelope. Is that to say > that on the positive portion of the square wave that the carrier is > oscillating between 0 and some maximum positive voltage, and conversely when > the square wave is negative, the carrier is operating between 0 and some > maximum negative voltage?

No. An amplitude modulated RF carrier can only decrease to zero, you can't have a negative signal level. It's like dimming a light; you can't make it any dimmer than the OFF position.

When a carrier is amplitude modulated, the resulting RF signal will have an instantaneous value ranging from somewhere near zero amplitude (corresponding to the most negative portion of the modulation signal) and twice the "resting" or no modulation RF carrier level (during the positive portion of the modulating signal.)

To put it another way, the RF carrier level will be zero during the negative portion of the modulation signal, and 200% during the positive portion of the modulation signal. (the unmodulated RF carrier level is equal to 100% for this example.)

> Is this the same as saying the voltage bias of the > carrier is alternating to a voltage of half the maximum levels of the square > wave, but the actual peak to peak amplitude is the same? If this is so, why > would this cause a difference in tube output?

No. The AM modulation process adds between 30 and 50% more power to the RF carrier output at full modulation, (depending on the modulating signals waveform) so you can expect the tube to become somewhat brighter if the system is working properly.

> Operating at very low > frequencies, the tube is seen to oscillate between a color characteristic of a > high modulation frequency, and a color which is the same as when the generator > is muted. One might think that except for the momentary pass through zero that > the plasma would look the same.

Many of the CB radios do not properly pass full modulation at low frequencies, which results is less than optimum modulation characteristics. The tube takes on a different color, depending on the particular modulating frequency used. If you use a system which directly modulates the RF, (such as mine does) so that the carrier wave is either ON or OFF, the RF output will follow the modulating signal directly even at low frequencies. In that case, some of these color effects are not as noticeable.

> Moreover there seems to be an extra glitch > during one of the half cycles.

I would suspect that this is caused by nonlinearities and distortion in the modulator stage of the CB. This is not unusual.

> Also, with all the talk of pulsed or gated generator output, it would be nice > if there were a switching device one could put in line from the generator. Is > there something out there that would function in that capacity, like an auto > blinker or something?

Probably there are, I'm just not aware of them, since I achieve the gate function through a different approach.

> I was looking at the clouds when you were studying electronics, > max

...if you don't look at the sky, you'll never get off the ground...

-- Ralph W5JGV


In the past two weeks, I had Mesa CB work up a couple of Uniden PC 66XL radios for me. They graciously allowed me to write down all the procedures they performed to modify these radios.I have been doing some destructive testing to see if the radio will hold up and so far it has. I need to put the data together and obtain some sources for the parts before publishing how to do the modifications. I will say that the mods are complex and may not be within the abilities of most people. I may be able to simplify these and have a sort of compromize that will still make a superior CB when compared to the 510.

The advantage of the PC66XL is that when modified, it will produce a pulse envelope that is almost double the intensity of a modified Uniden 510. In other words, the pulse has almost twice the modulation on it as does the Uniden. This translates as increased power at all applied audio frequencies. It should also mean increased effects. Strangely, even the peak power on my linear amplifers has increased about 10%. The 66 uses the same microphone plug and wiring arrangement as does the 510, so to change out all you do is replace the 510 if you are currently using one.

For the past several years, Mesa CB here in Albuquerque has been listed as a supplier of high quality coax cables, and CB radios. They have decided to sell fully modified CB's for those that ask. These will be modified to ISM specs with the speaker cut out, and the microphone bypassed and modified so that it takes a BNC connector. The cost for this service is reasonable starting at about 55 dollars for the PC 66XL . That is about 55 dollars plus shipping and the cost of the radio if you buy the radio from them. You can buy the radio elsewhere and ship it to them for modification. The price includes a new output transitor and other necessary parts such as a resistor, capacitors, and a diode. The CB is peaked for power with thier test equipment once modifications are completed.

Mesa CB offers a variety of high end CB's that will produce even more power when modified than the Uniden 66. Please call them for particulars and the cost of the modifications. They do take Master Charge and Visa. Be certain to tell them that you are using this in an R/B device, or they will not modify the microphone.

Mesa CB Phone 505-883-8080 Jim Bare


Jim Bares Latest revision book lists the Uniden PC66/68 XL. Ideally this Uniden is used as when properly modified it is capable of producing "twice the modulated power level of the Uniden 510 XL." ... "they will produce double the modulated power of any of the CB's in this book." It has been speculated because of similarities in the Cobra and this Uniden that they are one and the same. They definitely ARE NOT the same unit ! ... HOWEVER ... the Cobra WILL definitely work for our use and . In checking the history and discussing the architecture with cobra designers ... I found the uniden 66 is actually a knock-off of the cobra design. (At one time uniden and cobra worked much closer together rather than competitors) With FEW exceptions Jim's current modification instructions may be used to do an equivalent rework of the more readily available Cobra 25LTD. I did not even bother to photograph the differences. (Words actually work just fine here)

1. Diode D-9 on the Cobra is still designated as D-9 but is NOT located toward the front. It took some time to locate it ... but it is on the right side of the unit, halfway to the back, in the most open space of the unit. I DID confirm with Cobra's design engineers that this definitely is the equivalent diode to disable the modulation limiter.

2. it is not necessary to melt the wax out of the tuning coil L10 ... they use an elastic band ... just unscrew it and pitch it ! 3. The Uniden Jumper JV-17 is Designated as JP6 on the Cobra in the same general area. I was not able to locate locally the Shottkey Diode SR106 ... but instead was able to find the higher rated SR306 (which is capable of handling 3 amps as opposed to just 1) All the rest of the modifications are in the same general areas as Jim's book clearly indicates. The circuit board patterns are definitely very different ... but if you pay attention ... appropriate component location is pretty much straight forward.

In summary .... this seems to be a very good radio for $99. I was actually impressed. Even though I was making this modification for a fellow "rifer", I suspect I will be purchasing one for myself as time (and $$$) permits. During the testing, (I suspect due to its exceptional output), I was able to light one of Barry Allred's large triple bubble tubes somewhat with an unmodulated signal and NO amplification. This radio may be an excellent choice for a low power unit, (no linear amp), when paired with a small compact bubble tube similar to the type often made for the EMEM2 type devices. The "advantage" of this is that it is much cheaper, safer, and portable that the conventional units. I'm not sure when i will be able to follow up ... but will definitely post info here when I can. Jimmie H.


Some thoughts on Pulse rise and fall times. Some of these ideas were found out the hardway during attempts at modifying the Uniden PC 68XL. ..... || The std R/B pulse envelope has a rectangular in shape|| |...|

A minimal pulse envelope width will be equal to only the rise and fall times or a 1:1 ratiosuch as below. The envelope willassume adiamond shape. This sort of envelope shape will occur near the maximum audio band pass capability of the transmitter. This could be considered as a 1:1 ratio.

/\ /\ \/ \/

I would think that the minimal effective pulse envelope would have a 1:1:1 ratio.That is where the rise/envelope top/fall times are all equal. ./\ /\ \/ \./

If the rise/fall times the system is capable of is 1 us, then with a 1:1:1 ratio , the entire pulse envelope would consume 3 micro seconds of duration. With a 50% duty cycle, there would be 6 microseconds of overall period. That is 6 micro seconds from the start of one pulse to the start of another pulse.

To give everyone an idea of what is possible, a fully modified Uniden PC 68 XL will produce pulse envelopes with rise and fall times of 2 us. A partially modified 68 has R/F times of about 4 us. The internal audio chip will produce 1 us rise and fall times of the square wave.

Thus there are two limiting factors to R/F times. One is the radio circuitry, and the other is the audio chip. The ultimate limiting factor in an ideal transmitter would be that of the audio chip.

Rise and fall times are limited for a variety of reasons within the radio circuitry. One of the primary ones is the charge and discharge time of any capacitors in the circuit.

These are just some things for people to think about and perhaps work with.

Jim Bare


The microphone preamp level will affect the quality of the wave. Set too low,the system will lack modulation. There is a transistor amplifer circuit that is part of the microphone preamp circuit. If over driven by too much voltage from the square wave generator, this will cause distortion of the audio signal.I normally run my 68 Cb with the preamp knob set to max. Try reducing the input voltage of the square wave generator to no more than 1.4 volts P-P, or about 700 mv using a DMM.

Jim Bare


Finally got around to working out some mods on the new 510 XL. A bit of warning - these new boards apparently need a good fan to keep them cool. Some people that have modified the radio report they will only last about 20 hours without cooling!

The basic mod is to cut D203 . This is located at the back of the pc board near the output transistor. This is all that should be done to the radio at this time!

So far other mods have not helped power much. Still working on unit, hope to get more out of it. Lots of surface mounted componentson the board, which means it is hard to swap out parts.

Tried changing out final transistor to 2SC1969 - no power gain. This is very risky - there are some surface mount capacitors on the same tracings as the mounting leads of the final transistor. Damage these and you are in big trouble. Since there is no power gain, don't even try.

Tried spreading various coils - no power gain.

There is an adjustable inductor L203 - don't bother with. Adjustment will increase power, but will raise unmodulated power so high that it will blow out the switching transistors in your linear amp.

Bandwidth - will pass about 30 KHz OK. Makes about 18 watts PEP when modulated. This compared to a good 20 from a Uniden 68XL with minimal mods and nearly 40 wattsfrom the Uniden 68 when fully modified

Rise/Fall times are very poor - > 9 micro seconds. For example a Uniden 68 with minimal mods has R/F times of about 4 microseconds. Fully modifed 68XL's are about 2 micro seconds.

Will post when find anything worthwhile.

Jim Bare


Here are the final set of mods for 510 XL. I pretty well changed out or modified everything that was accessable, and these mods are all that will affect the unit. The big problem is that a lot of capacitors and resistors are surface mounted and can't be easily worked with. Thus they were left alone, which limits the capability of the CB. Also makes it run hot! This unit needs a good size fan to blow across the final output transitor and the audio chip.

Changing inductor values had no positive effect at all.

1. There is a row of 7 electrolytic capacitors that runs along the side of the pc board where the audio chip is attached. Replace the first one of the row, counting from left to right with the front of the board to your right, and the audio chip side of the chassis up. . This capacitor is next to transformer T2. Change from 47 uf to 470 uf@ 16 VThis will increase peak power by about 2 to three watts.

2. There are two 1000 UF capacitors next to T2 and T1 that are not in the row of 7 .The first 1000 UF cap is the larger of the two. Remove this larger capacitor,and replace with a 3300UF 16V electrolytic cap.. Be careful of the height of the capacitor as if it is too high, you won't be able to get the lid back on the unit.

3. In the row of 7 electrolytic capacitors, the 5th one from the left is 470 Uf. Remove this and replace with the 1000 Uf you just removed. Be careful and do not short out the jumper wire that due to the capacitors size will be underneath it.

When finished, these three mods, plus the cutting of D203 will produce about 20 watts PEP output. The rise/fall time of the pulse envelope will be about 6.4 microseconds, and the unit will pulse to about 50,000 Hz.

Jim Bare


68XL Mod:Change C63 to 470 uf@ 16 volts or more. This will drop the rise/fall times of the pulse envelope in a fully modified 68XL from 2 microseconds to about 1.7 microseconds.C63 is found near the right rear edge of the pc board.

There is a definite change in the tone in the system when this is done. Improves the pulse envelope shape under 700 Hz considerably.

Jim Bare


A couple of more mods to the Uniden 68 XL. These will help the pulse shape in the region of from about 100 to 400 Hz.

Change C99 to 470 uf@16V

Change C70 to anywhere between 47 Uf @16 V to 220 Uf@16V

You can use a higher voltage capacitor, but the size may get too large to fit easily.

Jim Bare