Ameritron AL-811 Amp - No grid current or power out

Discussion in 'Amateur Radio Amplifiers' started by WA6TXU, May 27, 2012.

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  1. WA6TXU

    WA6TXU Ham Member QRZ Page

    After having my AL 811 in storage for about 10 years, while living overseas, I recently tried to fire it up. Made all of the right connections. Have the nominal 1700 volts. Keyed the exciter (no drive ). Transmit light went on (relay works) and the plate current is 110 ma (what it should be). Then I applied more drive to get the required 50 ma of grid current so I could then adjust the plate and load controls. Result was no grid current, and no responses to plate or load adjustments, and no power out. Would this be an indication that during the 10 year layoff period, my 811s have gone bad, or could it be some other problem? Years ago, when I operated the amp, I never had a problem. I am driving the amp with my IC-735, which operates great running barefoot. Help! Thanks. Dave, WA6TXU.
  2. W1QJ

    W1QJ Ham Member QRZ Page

    50ma is not enough drive. Try more drive than that, Manual says 400ma of plate current for iniitial drive level. If that still does nothing then check the blocking capacitor(s). May be a bad solder joint or something.
  3. WA6TXU

    WA6TXU Ham Member QRZ Page

    The problem is that I am increasing the drive on my rig but it is not reflecting in increased grid current on my amp. In fact there is no grid current shown on the meter of the AL-811.
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    My first guess would be dirty/oxidized contacts at the T-R relay, so although the amp is "keying," the RF drive applied is not getting to the cathodes.

    Try cleaning the contacts using a piece of coarse paper (I usually use a dollar bill -- unless I'm feeling rich, then I might use a twenty!). A piece of paper soaked in WD-40 actually works even a bit better.

    Do not EVER use any kind of file or "spark plug cleaner" type tool. A very fine (soft, almost like skin) burnishing tool is okay, but actually a dollar bill works great and is coarse enough to clean contacts well.
  5. W1QJ

    W1QJ Ham Member QRZ Page

    The fact that you have 110ma or thereabout should indicate that the tubes are good. A dead tube(s) that would not produce normal idle current would probably not make any power either. But since your idle current is good you should be seeing output if the drive is getting to the tubes. Then it could be that the relay contacts are at fault. Once you get round to cleaning them which would not be a bad idea anyway, see if that corrects the problem. By the way, can you receive well through the amp? I know you say it works OK barefoot but just wondering about receiving. Does this happen on any band you try? DO you have a dummy load?
  6. KM1H

    KM1H Ham Member QRZ Page

    That is more than sufficient drive if he was actually getting it. The tubes are rated at 25ma grid current each so 50ma would give a respectable output as the starting point for tuning.

    The 110ma idle current says the operating bias and the rest of the DC path is OK. What does your IC-735 power meter say when you try using it? If its going into an open relay there shouldnt be any.

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