[Amps] Looking for help with AL-811 repair

[GGLL]

   Is  that the four tube version?. Afriend of mine has  a three 811 one 
AL 811 and can't obtain more than 300 watts without passing into the 
grid current red zone. I think those new 811 might be capable of some 
450 watts out at least. B+ voltage is ok.

Best regards
Guillermo - LU8EYW.

Mark Thompson escribió:

>I'm looking for some help in troubleshooting an Ameritron AL-811
>amplifier (600 watt version) and am hoping someone on the reflector can
>help.
>
>I can only seem to get about 200 to 300 watts of output power into a
>good 50 ohm load in CW mode.  After tuning the amplifier to the
>manufacturers specification I increase the drive to the amp and can run
>it up to about 300 watts when the output stops increasing.  The Ip
>stops increasing after getting up to about 300 to 350 mA.  The Ig
>starts to increase very rapidly at this point.
>
>The plate voltage is resting at about 1500 volts with no drive (a bit
>low) and decreases to 1350 volts under the described drive.  I have
>verified that the line voltage is 120 VAC and only drops to 118 VAC
>when the amp is driven.  All the diodes in the high voltage circuit
>appear to be good (measured using a DVM) in both the forward and
>reverse directions.
>
>I have also substituted a different 811 one at a time for each of the
>tubes with no difference in the results.
>
>Any suggestions on where to head next?
>
>Thanks,
>
>Mark  K2AY
>
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