Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- Ed -
Oscillations are a possibility, but unmodified T-4X's are pretty stable. The odds of two are more than astronomical! The VOX hanging _CAN_ account for high plate current with RF Gain all the way down. Once the relay is closed, the only thing limiting plate current in the finals is the grid bias. NO RF drive required. If the bias is too low, (or has high ripple,) the plate current will soar. That's one of the "features" of sweep tubes. They will draw LOTS of current at low plate voltages. The ground return is shared. I'd start with the AC-4. When you get to the transmitter, be sure and check the Final cathode resistors and the meter shunt resistor. Both are quite likely to have been damaged by your high plate current. 124 VAC is well within the AC-4 "120 VAC +/- 5%". "115 VAC" line voltage is a myth. The nominal line voltage has been 120 VAC for many years, well before the AC-4 was designed. The filament voltage is often a little high with T-4Xs because of the lower filament load vs the TR-4. Three (3) Amps for the T-4X vs 5.5 Amps for the TR-4. 73, Garey - K4OAH Atlanta Drake C-Line Service Manual <http://www.k4oah.com> [EMAIL PROTECTED] wrote:
Thanks for all the comments. Looks like the voltages may be reasonable given my high line voltage. I checked the ground between the AC4 and the transmitter and its OK. I checked the filament voltage and it is high also. I thought about the VOX hanging up but that wouldn't account for the high plate current with the RF gain all the way down. Maybe its a parasitic oscillation in the finals, but it would be a great coincidence if it occurred in two transmitters. Guess I'll pull the bottom off the T4XC and check voltages there, as well as try to figure out if the plate current is driven by DC bias or whether there is some RF drive. Ed
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