Post by G.Re
What is the reason the Fisher 30-A uses (very) different valued grid
resistors for the power tubes?
- R9 = 2K2 for V2
- R4 = 33K for V3
A later (or earlier?) 30-A version has no grid resistors, also no balance
circuit for the phase inverter.
* Typo, R4 must be R11
* No, R9(2K2) & R11(33K) are control grid resistors, see the schematic.
The schematic linked above is not accurate, here's a better one ...
... but for the question it does not make a difference.
probably did a 'cost reduction' version, and different resistor values
(in your case) as a hard-set "balance" of sort.
* That seems unlikely since there's a balance pot (R2).
Also see if the output transformer is actually driving the screens in
'ultra-linear' mode or not. Makes all the difference in the world for
screen circuit if it's ultra-linear... which may have NO screen
resistors - lots of things dependent on one another in design, screen
current limit, screen volt limit, whether or not it's ultra-linear and
where the taps are, supply voltage, bias, yotta yotta.
* No ultra linear mode here, see the shematic.
(aka 'Bombastic Bob' in case you wondered)
'Feeling with my fingers, and thinking with my brain' - me
'your story is so touching, but it sounds just like a lie'
"Straighten up and fly right"