On 17 Jul 2005 06:51:02 -0700, "Professor"
wrote:

Yes... I'm the designer. I used Pcad software for schematic capture and
PCB layout.

Professor
Check out FlashAlert at www.telstar-electronics.com

I've been looking at the design of several amps, and all amps are
definitely not created equal. The regulated bias supply is seldom
seen in the CB amp world.
I picked up a Palomar Elite 300 for study. It turned out to be a
study in what not to do.

Here is what I found so far;

1) The amp is zero bias. Sounds like Darth Vader with added distortion
on sideband.

Ok. I fixed that with a diode clamp. At least mine is in AB1 now.

2) The low and medium power setting is achieved by sending some of
the RF to ground via a single resistor. The input SWR goes through
the roof.

Ok. I replaced that with a 50 ohm impedance resistive t-pad.

3) The SWR delay is on all the time, and sometimes people responding
to my transmit get chopped off in my receive before the amp's relay
can un-key.

Ok. I put the delay capacitor for the relay on a switch.

4) Here is the weird one. The SWR without the amp on is 1.1, but
when I turn the amp on the SWR goes to 3.x:1 or higher, and I'm
talking about the SWR displayed on a meter AFTER the amp. Not the SWR
on the input side of the amp.

Hmm. This one stumped me, but some other smart fellows suggested the
amp has parasitic oscillations and the frequency (or frequencies) of
the oscillation(s) are outside the bandwidth of the antenna. I can
take another amp with two 3-500z tubes, and put it on the same antenna
with no substantial increase in SWR from the antenna. The Palomar
Elite 300 is only good for about 100 watts. The two 3-500s are good
for 1300 watts. The antenna is rated at 5000 watts.

I'm still working on the fix for this one. Tuned input and output
circuits would probably fix it, but there is not alot of space inside
the amp to work with.

5) The RF from the output transformer is not filtered from the DC
input to the collector on the finals.

Ok, I put an RF choke on the DC power cables to keep the RF from
running up the DC cables and tripping out my pwer supply.