11-02-2016, 03:07 PM
Ok Let's try the grid cap of the 77 IF amp tube. Can you hear the 400cy tone when connected there? If you can measure the voltage on pin 2 and 4 of the 6A7. If you can't measure pins 3 and 2. All of these pins should have some HV on them. If not you may have a bad (open) IF transformer.
Just as an aside, the cap on the 6A7 isn't the control grid it's the 4th grid which is the rf input grid. The actual control grid is grid 1 which is on pin5. In a pentagrid converter the cathode, G1 and G2 (acts like the plate and has HV on it) is wired as a triode oscillator, that's the bottom half. The top half is setup as a pentode amplifier ( this is where the input signal is applied to G4)
http://www.r-type.org/pdfs/6a7.pdf
Just as an aside, the cap on the 6A7 isn't the control grid it's the 4th grid which is the rf input grid. The actual control grid is grid 1 which is on pin5. In a pentagrid converter the cathode, G1 and G2 (acts like the plate and has HV on it) is wired as a triode oscillator, that's the bottom half. The top half is setup as a pentode amplifier ( this is where the input signal is applied to G4)
http://www.r-type.org/pdfs/6a7.pdf
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got it!
Terry
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