About 12 years ago I helped install a Harris 2.5KW (I think) AM transmitter for use on 1350. I remember PWM. Can you recall what Class of operation it was/is? The output was solid state.
Regards, John
You might be thinking of the Harris SX-2.5, but it used PDM, not PWM. If it was the SX-2.5, its r-f output FETs operate(d) Class D.
Ahhh, that's it. Thanks. The efficieciency was around 70% then? I know at 1KW is was basically stone cold 24/7. The "Chief Engineer" picked the wrong tap on the transformer and when there was a slight voltage fluctuation the transmitter would trip and go offline. The owner threatend Tampa Electric with a lawsuit. TECO said the voltage fluctuations were well withing range after placing a recorder on the input to the transmitter. I called Harris and they politley guided me through the procedure. If I remember correctly, the "Engineer" had it strapped for 208 and the input was 240.
The d-c input to r-f output conversion efficiency of the output FETs in the SX transmiitters is 85%.
The total input power from the a-c mains to 100% sine-wave-modulated r-f output power shows an efficiency of about 70%, including a-c power for internal forced air coooling.
Maybe the station where you had to re-strap the transfomers was not the original purchaser? On new orders, Harris always set the taps based on information they got for the installation site from the buyer, during the final test before shipment.
"Maybe the station where you had to re-strap the transfomers was not the original purchaser? On new orders, Harris always set the taps based on information they got for the installation site from the buyer, during the final test before shipment."
You hit the nail on the head. It came from 1340-WTAN in Clearwater. We changed the crystal to 1350 for WDCF. Once the power supply was strapped correctly it ran like a charm. A very nice transmitter.
As someone who is just a hobbyist in
this sort of thing - I have to admire
you guys.
You are the real deal.
Bruce, DOGRADIO
Yes, sometimes I forget stuff and I get jarred back into reality. Now the Harris transmitter I was chatting about replaced an old Gates BC1G. When I was hired at WDCF I discovered that the owner was a first class cheapskate. The transmitter would routinely shut down every 15 minutes or so and he would re-satrt it. This had been going on for several months. What he did not know was there was a thermal relay that was inside a tube in the power supply section. The purpose of the relay was to allow the 833 finals/modulator tube to fully warm up before high voltage was applied. The relay at 2002 prices was about 75 bucks. When I told him this was the problem he threatened my with my job if I was wrong. Needless to say it fxed the problem. He also did not understand audio processors, so therefore he had none. It gets better, he also owned WZHR and the modulation transfomer had a short circuit to the core. So rather than fix that he had me place it on a piece of plywood so it would be isolated from the chasiss of the transmitter and not kick the breaker. True stories.
Here is what the Gates transmitter looks like: http://w4neq.com/htm/gates.htm
Those are great stories!
My friends who work in broadcasting
here in the Hartford, CT area have told
me stories that don't sound too different
from yours, above. I seem to remember
one local BC engineer who really got chewed
out because he bought a second roll of solder
for the radio station with the station's money.
(Or maybe WITHOUT.) It didn't make
any difference to the station's owner (or GM,
or whatever.) The guy said something to my
friend like, "Oh Bruce, what you DID! The awful
thing you DID! Don't EVER do that again!"
YUP, true story. (Name changed to protect
my friend.)
Those are absolutely GOUGEOUS pictures of
that transmitter!
What a great thing to do -putting it
on 160 meters!
I'm going to go back and look at the
pictures again.
Bruce
Glad u liked to story and the pics