Followup:
* Death Cap Removed!
* Chassis ground installed (Crimped, soldered, and star washered to the PT bolt after sanding chassis connection point)
* Rewired to put fuse and switch inline instead of on either end of the ac.
* PSU-style filtered plug installed in unused rectifier hole. (unit has a SS rect)
* Cleaned Pots and chassis.
* Rudimentary test of caps to rule out short's or opens.
TODO:
* Buy and Install Progressive Double pole switch /w 'standby' switching the b+
? Any opinions on whether to use a guitar amp style standby or a turn-on delay relay?
* Re-Bias 6L6GC's
* Recap - Using Sprauge's because that seems to be what the rest of the amp uses.
? I was planning on using stock values 10, 20, 30uf @ 450-500v, are there any advantages to going bigger on these?
* Calculate impedance on inputs. (instrument vs line)
I fired it up * BRIEFLY* to make sure all was good, and when warm I got a beautiful, loud, clean sound with a faint 60hz. Shut it off after I verified operation, in case tube bias is too far off.
Folks, this is what you get when you buy tube gear off craigslist from some hippies in a van in a supermarket parking lot. In the end, i still think i got a good deal at a hundred.
Hello
Well it looks like progress is happening and good for you.
Things will be much better with that grounded AC supply and no cap to chassis. I have a repair bench horror story (of many) I might have to share with the forum sometime on those older amps getting plugged into a grounded mixer....oh boy..
Anyway, on the electrolytics you mentioned about replacing, with the age of the amp, they are all likely getting pretty dried up inside and losing capacitance besides potential of becoming leaky with regards to having literal resistance to ground common....
When they sometimes fail to the point of being very low resistance, a tube rectifier might exhibit some pretty purple flashes inside the tube, while it destroys the rectifier.
The original values on main filters should be a reasonable reference for replacement caps. I wouldn't stray too far from the current caps value but in your case, who knows what a previous person put in there, unless they all appear to be original parts.
The tolerance on the uF rating of these caps is pretty wide.
A 20 uF (likely 22uF) new cap might measure around 20 or considerably more and still be ok to use. Of course don't use too low of voltage rating...
It was a good idea when you only ran the amp briefly for the sake of the outputs possibly being underbiased or no bias at all. I have replaced outputs before that had actual holes where the plates melted. And likely a very large fuse was installed to "fix" the amp...more than one time I have found a 20 amp automotive fuse in the fuse holder...
A residual hum could be from dried out filter caps and other things are always possible. If the 6L6's are pulling a huge current from either internal shorting in the tube or very low or zero bias, that will pull the power supply down hard enough to have excessive ripple, regardless of the effect of PP cancelling minor ripple.
I have received amps that guys bought off of ebay and they were shocked at what work was needed to get the amp rolling again. I know what you mean about the 'unknown' when obtaining used gear.
Sounds like you will have some enjoyment working your way through this project.
Carry on