Palomar Elite 250 transistors

[Robb]

Best bet would be to have a good tech with a scope bench test the radio. Did you buy it new or used? If it was used there are ways to defeat a limiter without clipping it out. . .

Agreed.
The scope is the best way to see if modulation is going over 100%.
My short experience with modulation meters steers me away from trusting them any more; just not dependable nor accurate.

BT:
Another thing is make sure those copper coils in the back of the radio have not been spread apart too. If they are; then push them back together. They are part of the 54mhz trap circuit and they will throw off a 2nd harmonic if they have been disabled by/thru the spreading of those coils. Dumbest mod I've ever seen next to clipping the limiter. That alone could have created this problem for you.

I have to assume that if you are getting 30 watts out of that 959, then it has to be the MOSFET version. Which is the way they are building them over the past few years IIRC. Having said that, think I would set the hi power setting to ~15 watts on a Dosy for AM. Set the ALC for SSB to the same power level. Even though that Dosy might be reading just 15 watts peak, it is probably - in reality - putting out closer to 20-22 watts peak. This way, you know you won't be sending off harmonics and spurs and it will be cleaner sounding than you think it is now. Your amp may see a few more watts out with a 30 watt output; but it may fail prematurely if you take that route. That amp's input was designed for 20 watts - peak - IIRC.

Probably won't need that low pass filter if you just make the radio right in the first place - IMO . . .

Have fun.

 

[psycho]

Ok guys I got this figured out and fixed. I added my Low Pass Filter inline right after the radio and before the amp and the swr went down to 1.1 on the radio meter and Im getting much more swing out of radio and the amp now. On high side im dead keying 1 1/2 watts and swinging to 180 watts now. That is fine to me on low side im getting right at 100w and swr is 1.1 with amp on or off now. I guess the low pass filter is taking out all the unwanted harmonics that was making my swr go up. My filter is a drake tv-3300 i think.

You must have added coax to put the filter in line. Sometimes changing jumper lengths can alter SWR readings.

 

[mr_fx]

well that seems right, 2sc2290 transistors @ 12.5v are only 60 watt units

60 x 2 = 120
@ 14.4v they might do closer to 70 watts so 140 for the pair... well there you go

 

[basstracker1970]

Well all I do know for sure is that it is working great now that I added the low pass filter in between the radio and amp. Swr's are great now and it's puttin out the swing. Thanks guys for all your insight to this problem 73'ssss to you all. I do Have a like new Rm Italy KL-60 I would let go for 45.00 shipped. I can send you pics of it if interested.

 

[basstracker1970]

Does anybody know how to fix the relay chatter on ssb with this amp ?

 

[Shane smith]

I have the same box but mine has 2879's in it,is it possible to make it work on ssb? I'd like to figure out what need to be done....

 

[nomadradio]

Good chance that it's a waste of time. A capacitor added to the keying circuit is what the "SSB" switch is connected to in an amplifier that has it. It stores enough charge to keep the relay closed for around a second after you unkey. But that's all it does, is to slow down the relay.

Most amplifiers like this one were built to appeal to truck drivers running AM only.

Odds are that it contains no source of bias current to the input side of the RF power transistors. The radio's carrier is what turns on the transistors, and keeps them turned off in receive mode. The extra components needed to switch this bias current on and off when you key the relay does several things.

First, it prevents the amplifier from sounding like trash with a sideband drive signal.

Second, it reduces the efficiency of the amplifier when running AM. Anything that cuts the power from a CB linear hurts the sales potential. As a result, the bias circuit that's necessary to make SSB sound right gets left out both for this reason and to reduce the production cost.

Just taming the relay to stop the chatter is only the cheap half of making an amplifier work on sideband. The hard part is the bias circuit. Pretty sure this amplifier doesn't have one. If not, you will sound like a s41t salesman with a mouthful of samples using it on sideband.

73

 

[Tallman]

Ok guys I got this figured out and fixed. I added my Low Pass Filter inline right after the radio and before the amp and the swr went down to 1.1 on the radio meter and Im getting much more swing out of radio and the amp now. On high side im dead keying 1 1/2 watts and swinging to 180 watts now. That is fine to me on low side im getting right at 100w and swr is 1.1 with amp on or off now. I guess the low pass filter is taking out all the unwanted harmonics that was making my swr go up. My filter is a drake tv-3300 i think.

You can bet that the tweak and tune messed up your radios ability to filter out the Harmonics. Your harmonics are twice the frequency of your primary signal. Antenna tuned to 1 through 40 and toss all of those harmonics in there and your SWR goes higher. SWR meters do not filter out the harmonics.
Good deal on the filters. It worked as expected.

 

[Shane smith]

Good chance that it's a waste of time. A capacitor added to the keying circuit is what the "SSB" switch is connected to in an amplifier that has it. It stores enough charge to keep the relay closed for around a second after you unkey. But that's all it does, is to slow down the relay.

Most amplifiers like this one were built to appeal to truck drivers running AM only.

Odds are that it contains no source of bias current to the input side of the RF power transistors. The radio's carrier is what turns on the transistors, and keeps them turned off in receive mode. The extra components needed to switch this bias current on and off when you key the relay does several things.

First, it prevents the amplifier from sounding like trash with a sideband drive signal.

Second, it reduces the efficiency of the amplifier when running AM. Anything that cuts the power from a CB linear hurts the sales potential. As a result, the bias circuit that's necessary to make SSB sound right gets left out both for this reason and to reduce the production cost.

Just taming the relay to stop the chatter is only the cheap half of making an amplifier work on sideband. The hard part is the bias circuit. Pretty sure this amplifier doesn't have one. If not, you will sound like a s41t salesman with a mouthful of samples using it on sideband.

73

Thanks for the reply, I appreciate the information..