[Amps] Looking for help with AL-811 repair

[Steve Katz]

	[Steve Katz]  De WB2WIK/6 comments below..... 



> 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.
> 
> //Sounds like a too-low plate voltage problem to me.  Have you tried
> re-tapping the transformer to kick the B+ up to where it's supposed to be?
> 1350v x 350ma = 472.5W.  If you're getting 300W output power, that's about
> right for such low input power.
> 
> 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?
> 
> //I'd try higher B+, available by re-tapping the transformer. Don't know
> what the default setting is with the AL-811, but the default in some other
> Ameritron amps seems to always be the wrong one for me.
> 
> Thanks,
> 
> Mark  K2AY
> 
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