Thread: Fisher 30-A amp
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G.Re G.Re is offline
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Default Fisher 30-A amp



"Big Bad Bob" wrote in message
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On 2020-03-03 01:08, G.Re wrote:


"Big Bad Bob" wrote in message
...

On 2020-03-01 00:56, G.Re wrote:
* No, R9(2K2) & R11(33K) are control grid resistors, see the schematic.
The schematic linked above is not accurate, here's a better one ...

http://www.fisherconsoles.com/non%20...030-a%20sm.pdf
... but for the question it does not make a difference.

oh I get it. yeah flickr links are most likely "scripty" and I don't do
them (as in 'must I allow script and lower my security JUST to view this?')

I also noticed a fixed screen voltage supply with NO series resistors
* The earlier version of this amp has 68Ω screen stoppers, no idea why they
left them out in this (later) version.

Grid series resistors like those are typically there to limit grid
current in an AB2 situation. However, different values MIGHT introduce
non-linearity when it starts to clip. I have to wonder why they would
do this. The balancer pot would allow you to adjust for different gain
factors on the tubes as well as imprecise resistor values in the cathode
and anode circuits. So no indicator as to why they did different series
resistors on the control grids...