Motorola console amp rebuild

[maxkracht]

I'm planing to rebuild this thrift store console amp and try out a few bits of circuitry. Does this schematic look reasonable? Has anyone tried a garter bias setup before?
Any thoughts or opinions are appreciated. Thanks!

IMG_2492.jpg

IMG_2491.jpg

IMG_2488.jpg

[martin manning]

It's new to me. Write up and mods here: https://www.tubecad.com/2009/04/blog0163.htm Looks to be in pretty good shape inside. Does it work?

[maxkracht]

Looks to be in pretty good shape inside. Does it work?

Yes! Only issue is a sticky/scratchy volume pot, but everything else works. Haven't fully tested the tubes or measured the output transformer, but everything functions and sounds surprisingly good, in a plugging into a "hifi" sorta way. Not bad for $20.

[maxkracht]

https://www.diyaudio.com/community/thre ... er.313318/ Here is some info on that circuit's history, not a Blumlein invention. I get the sense that this is a well-known thing in the hifi world. Might be a useful trick if you need to lower the voltage in a cathode biased amp. More work than adding some zeners, but with the added benefit of tube matching.

[maxkracht]

Think i'm mostly finished with the electronics part, probably won't get to a cabinet for a while. Need to play with it a bit more, but I'm liking it so far. Nice clean sounds with the original 12au7s, but I think I prefer 12ax7s, at least in v2. Having independent tone controls is nice, lots of range. Garter bias seems to work fine, though I haven't plugged enough tubes in to find an extreme mismatch. Got a bit crowded around the power tubes, so it's probably not practical for everything, but I might try it again.