AerialBoundries
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Hi all - I recently picked up this silverface VR and am in the process of making a few changes. I'm no expert but do have a technician degree with a fair amount of bench time (a bit rusty but yes, I can safely discharge caps), but have never done this kind of work to a vintage amp so I have a few questions.
First, the bias balance circuit:
I have started to convert this to the adjustable circuit by removing the 3.3k resistor from the bias supply to the pot and the 50mfd 70vdc cap that was connected to ground. I moved the 15k resistor to the top leg of the 10k linear pot, connected a wire from the bottom leg to the bias supply and connected a wire from the center pin to the 100k resistor on the board (bias splitter? not sure what this is called). My question here is regarding removal of that 100k and installation of the 220k resistors as per the earlier design. How will this affect the sound? Should I be using CC here?
Filter caps:
Next, I installed a 3 prong cord (removed AC receptacle and ground switch) and replaced the filter caps with F&T 16uF 475v versions. The resistors installed in the doghouse with these are 10k and 2.2k, which I am planning to replace with equivalent 3w metal film versions. I didn't think there was a reason to stick with CC here, anyone feel differently?
Next, the bias supply.
So, I have an F&T 100uF 100v cap that I'm installing in place of that Mallory, and was thinking of using another metal film resistor to replace that 1k CC resistor. I believe the original is only 1/2w - what is recommended for a replacement?
Next, plate load resistors:
I was thinking of trying a 12ax7 in the PI for some extra gain - are the 47k plate resistors still appropriate in this config?
General question about plate resistors - I was thinking of leaving them alone and seeing how the amp performs with the other changes, but I'm also tempted to just change them while I'm in there now. Sorry to rehash this again, but there seems to be different views of what type of resistor is best here. I do have some 3w MF in the appropriate values (47k, 100k), but I'm wondering if I should just stick with CC? The Ohmite Little Demon series are available in 0.5w-1w and they would certainly look the part but performance is #1 for me. I guess I don't fully understand where it makes sense to stick with CC over MF.
Of course, pretty much any of this is reversible but I'd like to get as much done in this first pass as I can. Next on the list is to replace the 7 electrolytics on the board with 25uF 50v Sprague Atoms.
OH I almost forgot - my power tubes have 470ohm 1w CC screen resistors and the 2000pf caps. I was thinking of clipping the caps and replacing the CC resistors with MF - is this the standard, and what power rating do most people go with, just 1w?
I'm awfully tempted to go through the entire amp and clean up the wiring but I'm thinking this is bad form. I understand that wires are run a certain way to reduce noise, so I think I'll just get it back together and see how she sounds.
Thanks for reading and for any suggestions/comments!
First, the bias balance circuit:

I have started to convert this to the adjustable circuit by removing the 3.3k resistor from the bias supply to the pot and the 50mfd 70vdc cap that was connected to ground. I moved the 15k resistor to the top leg of the 10k linear pot, connected a wire from the bottom leg to the bias supply and connected a wire from the center pin to the 100k resistor on the board (bias splitter? not sure what this is called). My question here is regarding removal of that 100k and installation of the 220k resistors as per the earlier design. How will this affect the sound? Should I be using CC here?
Filter caps:

Next, I installed a 3 prong cord (removed AC receptacle and ground switch) and replaced the filter caps with F&T 16uF 475v versions. The resistors installed in the doghouse with these are 10k and 2.2k, which I am planning to replace with equivalent 3w metal film versions. I didn't think there was a reason to stick with CC here, anyone feel differently?
Next, the bias supply.

So, I have an F&T 100uF 100v cap that I'm installing in place of that Mallory, and was thinking of using another metal film resistor to replace that 1k CC resistor. I believe the original is only 1/2w - what is recommended for a replacement?
Next, plate load resistors:

I was thinking of trying a 12ax7 in the PI for some extra gain - are the 47k plate resistors still appropriate in this config?
General question about plate resistors - I was thinking of leaving them alone and seeing how the amp performs with the other changes, but I'm also tempted to just change them while I'm in there now. Sorry to rehash this again, but there seems to be different views of what type of resistor is best here. I do have some 3w MF in the appropriate values (47k, 100k), but I'm wondering if I should just stick with CC? The Ohmite Little Demon series are available in 0.5w-1w and they would certainly look the part but performance is #1 for me. I guess I don't fully understand where it makes sense to stick with CC over MF.
Of course, pretty much any of this is reversible but I'd like to get as much done in this first pass as I can. Next on the list is to replace the 7 electrolytics on the board with 25uF 50v Sprague Atoms.
OH I almost forgot - my power tubes have 470ohm 1w CC screen resistors and the 2000pf caps. I was thinking of clipping the caps and replacing the CC resistors with MF - is this the standard, and what power rating do most people go with, just 1w?
I'm awfully tempted to go through the entire amp and clean up the wiring but I'm thinking this is bad form. I understand that wires are run a certain way to reduce noise, so I think I'll just get it back together and see how she sounds.
Thanks for reading and for any suggestions/comments!

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