The AM Forum

Is there anyone else here running a Collins 300G broadcast transmitter?  I would like to know what you are driving it with and the method of drive connection.  I have one but can't seem to get enough drive out of the original 807's to drive the  810 finals.  Anyone?  The tube specs say the 810's require about 15 watts drive but that is not the case with mine. It requires 80-100 watts and the 807's (2) just won't do.

Paul/WA3VJB has one.

Maybe a little more information is needed? How much grid bias is there when you excite the tubes? The tube manual says it should be -200 volts. Perhaps it biased way beyond cut off? The specs also say it take 17 watts per tube for drive. Given circuit losses, it may take at least 50 watts from your exciter. With no drive, what is your grid bias voltage and plate current?

Looking at the parts list, it looks as if the bias resistor R-116 is 2000 ohm. Is it 2000 ohms or did it deteriorate and go to a higher value? Is it hard wired or a clip in type? If it is a clip in type, pull it and make sure there is no corrosion on it.

I found the book


http://collinsradio.org/archives/manuals/300gManual.pdf (http://collinsradio.org/archives/manuals/300gManual.pdf)

Mine's not hooked back up yet, but when Barry Wiseman was running it in CO he just had an external VFO plugged into one of the crystal oscillators in place of the crystal oven and had external audio gear running to the input strip on the bottom front left near the AC. I don't think it was anything substantial in the power dept.

Follow Terry's advice and if that doesn't solve it, I'd check with Tom/W2ILA here on the board. He's the 300G ghuru in my book and has had several 300Gs pass through his hands. Send him a PM and see what he says. He does travel for work at times, so be patient.