[TMC] This darn amp

[Chris Bolkan]

Hi TMC lovers!


Got the power supply corrected. Now puts out a nice solid 360V to the final
screens and all other voltages are correct.

The good: All voltages correct, finals now bias nicely just as I think they
should and it tunes up nicely.

The bad: At 240ma plate current, single tone with a drive of 20, it puts
out 120V p-p into a 50 ohm load. That calculates out to 35 watts RMS and is
almost exactly what the inline wattmeter shows. Even when I pump it up to
over 300ma it only puts out just 50-70 watts. I don't like doing that for
long as occasionally the breaker trips because I have it set conservatively
until I figure out what is wrong.

So correcting the screen voltage and making it all "right" still did not
change the output power. That's what it was before even with what I
consider a profound change.

This is also puzzling: There is no change in screen current (on the meter)
no matter what I am doing tuning this thing up. The meter reads very close
to 0 (about a third of the way up the scale as it should, but nothing I do
changes screen current. I verified the proper screen voltage on the final
tube socket pins so I know the sockets are not shorted. Since the screens
get their voltage off the measurement divider, if the current is changing
it should register.

I still have not checked the capacitance on the screen pins of the sockets
yet. If those were somehow low would that have a degenerative feedback
effect? Even so it seems highly unlikely that both sockets have failed in
exactly the same way. This is so confusing.

I've been posting a bit lately about my PAL 350. I've not seen a single
comment so I guess I don't know if the posts are even going out. Well,
here's the latest. Any ideas would be greatly appreciated!

Chris