So I've been tinkering with my Scott 222c lately which honestly hasn't seen a ton of use since I've been on my Fisher high. This was rebuilt by AK'er Bricktop. Micah did some of the nicest work I've seen underneath installing bias test points and everything. Now I understand how the balance pots work. I installed my nos matched quad of 6p14p-eb's from McShane. Adjusting the balance pots here are my current draw measurements.
First pair - both drawing 10ma
Second pair both drawing 9ma
So I flip the amp over and have it running (no 5ar4 in place) to measure voltages I'm getting on pin 2 of each 7189.
tube 1 -17.7V
tube 2 -17.8V
tube 3 -17.8V
tube 4 -17.6V
Nice all 4 tubes are pretty closely matched. :thmbsp:
Also to add because they are all related, measuring the voltage off the bias supply to the first 12ax7 in the series I get -47.7 Seems where it should be (11.9V/12ax7).
Now I'm trying to make the voltage less negative before the balance pots for the outputs so I can get the tubes about 22-23ma/piece because as they sit now they're running ice cold. Surprisingly the amp still sounds great but as I've experienced with my Fisher that was running ice cold, it's a whole new ballgame when they're running in the sweet spot. :yes: I've searched around and this has been discussed but not in enough detail for me. I was paying attention to http://www.audiokarma.org/forums/showthread.php?t=288528&highlight=scott+222c&page=10 and gathered alot of info but am not quite confident enough to dig in on my own.
Now -47.7 comes off this point and a wire feeds it straight to the balance pots and series of 12AX7's
Here is a nice shot of all Micah's work
Any finally a nice top shot
Carefully installing the 5AR4 to measure the B+ gives me 433 volts. Wall voltage is measured at 115V on the nose. Well within 10% of 420V listed on the schematic :thmbsp:
Now is it as simple as installing a pot in between the line coming from the bias supply to both balance pots? If so what value would you use? I'm a bit lost on this one. The Fisher fixed bias units are very straight forward where you just throw a 10K pot in place of a specific resistor.
Kory
First pair - both drawing 10ma
Second pair both drawing 9ma
So I flip the amp over and have it running (no 5ar4 in place) to measure voltages I'm getting on pin 2 of each 7189.
tube 1 -17.7V
tube 2 -17.8V
tube 3 -17.8V
tube 4 -17.6V
Nice all 4 tubes are pretty closely matched. :thmbsp:
Also to add because they are all related, measuring the voltage off the bias supply to the first 12ax7 in the series I get -47.7 Seems where it should be (11.9V/12ax7).
Now I'm trying to make the voltage less negative before the balance pots for the outputs so I can get the tubes about 22-23ma/piece because as they sit now they're running ice cold. Surprisingly the amp still sounds great but as I've experienced with my Fisher that was running ice cold, it's a whole new ballgame when they're running in the sweet spot. :yes: I've searched around and this has been discussed but not in enough detail for me. I was paying attention to http://www.audiokarma.org/forums/showthread.php?t=288528&highlight=scott+222c&page=10 and gathered alot of info but am not quite confident enough to dig in on my own.
Now -47.7 comes off this point and a wire feeds it straight to the balance pots and series of 12AX7's
Here is a nice shot of all Micah's work
Any finally a nice top shot
Carefully installing the 5AR4 to measure the B+ gives me 433 volts. Wall voltage is measured at 115V on the nose. Well within 10% of 420V listed on the schematic :thmbsp:
Now is it as simple as installing a pot in between the line coming from the bias supply to both balance pots? If so what value would you use? I'm a bit lost on this one. The Fisher fixed bias units are very straight forward where you just throw a 10K pot in place of a specific resistor.
Kory
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I really do love this Scott. Every time I take some pics to sell so I can fund another project I can't do it. I'd be hard pressed to find another example as fine as this one. This is truly a lifetime keeper. 
