With a B+ of 174Vdc what plate resistor and cathode resistor values would I need to properly drive an external 10K to 90K driver transformer for a pair of 45 tubes? Got distortion which I didn't like so I decided to rewire it as original. Tried the mod and got some hum which I cured by moving the cathode follower B+ to the same feed as the first audio tube. If not for the compactness of the R-390 I could get an Edcor 10K to 600 ohm transformer which has a frequency response to 20Hz and just use that in place of the audio transformer, but I know the Edcor transformer is way too large and will not fit at all. I too normally don't like to make mods unless they are beneficial and can be easily put back stock without any indication a mod was done. The R-390 has two filters and one selection on the audio response switch that is wide which means no filter at all.īasically what I'm wanting is to make the output voltage of the cathode follower equal the output of the transformer for the same input voltage to the first audio stage.
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