I picked up a VM mono amp for a harp amp conversion. It has a pentode first stage with what appears to be an hum balance on the screen. I hadn't seen this before, just curious if others had.
[img:720:527]http://lh6.ggpht.com/_jpUbIh2UclM/Sr__9 ... 10007r.jpg[/img]
In addition to the hum balance it has a couple of other interesting features - the DC coupled PI and the 200 pF cap on one of the output tubes grids. I don't think it had been modified but you never know. The chassis had to be unbent just to get inside of it.
[img:640:480]http://lh3.ggpht.com/_jpUbIh2UclM/Sr-IV ... CF0001.JPG[/img]
Interesting hum balance
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Andy Le Blanc
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Re: Interesting hum balance
haven't seen that balance either, slick... I have seen that inverter
The little cap on most other inverter types is on the other leg of the push-pull.
It may be more important that it is right on the grid .... radio interference?
The little cap on most other inverter types is on the other leg of the push-pull.
It may be more important that it is right on the grid .... radio interference?
lazymaryamps
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FUCHSAUDIO
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hum balance thingee
My guess is the extra grid is being used to leak some of the ac from the filament and cancel out the hum...? Note that it's the suppressor grid, not the screen grid, which is fed off its own supply. Cute.
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