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Discussion Starter · #22 ·
Client had requested 1 watt 470R screen resistors, .1 coupling cap in the first vibrato channel gain stage and two remaining power caps changed out...the coupling cap will probably reduce the noise on the vibrato channel volume pot and the remaining fresh caps may solidify the feel of the amp in general.
Will bag up the old parts to stay with the amp and use comp resistors, F&T lytics and sozo coupling cap
 

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Discussion Starter · #23 · (Edited)
Gas Auto part Cuisine Metal Font
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After the f&t power cap install all the background noise when turning the volume pot is eliminated....one of the old EH 6v6 had overheated at some point to cook the blue printing to grey....new set tung sol matched set 6v6gt and biased with output transformer resistance method(maths involved ala mr. robinette)😉
Very happy amp now....picking up 1 watt 470r tomorrow morning and job done as requested
 

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Discussion Starter · #25 ·
Sorry to rain on your parade, but adjusting negative bias voltage is not proper way to adjust bias current.
New tubes are different than old stock and most likely that -35volts doesn't really follow requirement for bias current.
It might work but I would prefer to measure bias current.
Gotcha loud n clear. Thanks
 

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1965 Fender Mustang, Ampegs, anything to test an amp.
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Years ago I built a plate current fixture to allow the monitoring of octal, pin 3 plates. I used an analog meter from a defunct VTVM and calibrated it for 100mA full scale deflection or FSD, through selection of the correct shunt resistor for 100mA FSD...custom made.
It has a switched, dual adapter interface that enables me to conveniently monitor a dual output configuration.
It is a low cost test fixture if you can scrounge up the parts.

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Discussion Starter · #27 ·
Years ago I built a plate current fixture to allow the monitoring of octal, pin 3 plates. I used an analog meter from a defunct VTVM and calibrated it for 100mA full scale deflection or FSD, through selection of the correct shunt resistor for 100mA FSD...custom made.
It has a switched, dual adapter interface that enables me to conveniently monitor a dual output configuration.
It is a low cost test fixture if you can scrounge up the parts.

View attachment 450397
Very cool....i was reading about this type of contraption recently: the author had used two or three hand held meters in unison to achieve the result until he built similar...I used to have a simple store bought version called a BiasKing ? once..not sure where it went🤪
thanks Paul
 
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