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Author Topic: Plates overheating on a 4-400A Tetrode Edward Jurich Master Film Handler Posts: 305 From: Las Vegas USA Registered: Jul 2003 posted 10-11-2003 11:16 PM                     If the plates don't glow, current normal with no modulation, but are red with high current under modulation and unable to make 100% modulation I'd first make sure it wasn't a bad match. How does the transmitter perform into a good 50 ohm dummy load. Modulate with tone and check modulation. Make sure the output network is tuned properly into the dummy load. If that's not the problem, look for a modulator problem. That bias supply could be suspect if you can't adjust the glowing down by adjusting the bias. I'd do all my trouble shooting into a dummy load. I used to run my 4-400's biased to glow red some under modulation, they'd sound much better that way. Hey, anyone still using mercury vapor rectifiers  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 10-12-2003 12:18 AM                     Edward, mine do. With zero modulation, they cool down. I thought I had a parasetic oscillation somewhere, but that was not the problem. Anyway, I just "accepted the fact" that they are going to glow. The transmitter still sounds OK. But I am not getting the mileage out of them like I do in the Collins.  |  IP: Logged William Hooper Phenomenal Film Handler Posts: 1879 From: Mobile, AL USA Registered: Jun 99 posted 10-13-2003 01:19 AM                        I think I am. They're the ones that emit that colorful gas, right? They're between the booth & the toilet, so you can't be sure which deadly gas is going on at the time.  |  IP: Logged Edward Jurich Master Film Handler Posts: 305 From: Las Vegas USA Registered: Jul 2003 posted 10-14-2003 09:34 PM                     Hey Bill, you better be careful with that gas, don't forget you're running carbon arc's  |  IP: Logged

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