An Amp Project for Cyg

[Cygnus X1]

To answer my own Q;, the green wire is still not a certainty, but it doesn't matter at this point.

I checked everything out that I could without power, and no obvious shorts, or other glaring issues, except a canister cap that serves as the power filtering, and one leg is for the power tube grid leak bias circuit. Capacitance tested ok, but that doesn't mean much on an electroytic that has shot the wad.
So, I stuck some tubes in it, and got my answer fast...A nice smooth, 120HZ hum through the speakers, and a PT that heated up real fast. So, good news, no shorts, bad news, that rare can cap is shot.
Start digging around for another cap or two to make things work...and I found an old switching pot that might work for the tone/switch control. Cool. Also found a NOS cap
with two lugs, same value. Screw it, let's try re-forming it while I shop for the replacement cap. I can use another electrolytic for the grid bias.
So, that's where we're at right now.
I still think the green wire goes to a neg. feedback circuit. We'll see.

[fett]

I didn't yank anything.:ROTF: Well maybe a few chains. But. I didn't mess at all with the amp other than clean it up a bit. And I made sure I didn't disconnect any wires. Honest.

[Cygnus X1]

The neg. feedback was there to reduce noise and internal ground loop issues.
(That is, if that's what is was there for...)
Still forming up the old cap, before buying anything, becuase we might also be looking at a shaky PT, or a funky OT. Who knows how much abuse this amp suffered? If someone ran it just a few minutes too long with the cap blown, it could have taken out the tranny's. It takes a long time to form a cap, so we'll see.

[fett]

Fix it. Damnit.:ROTF: This has gone way beyond cost. This amp just needs to work. Spend what you will on parts. I will pay for whatever it takes. Up to 99 cents.:ROTF:

[Cygnus X1]

(Busy digging through parts boxes, not looking up....)

[Cygnus X1]

1:15 AM Eastern Standard Daylight Savings Time
UPDATE:
Forming caps.
(Look it up, it's amp alchemy in the making).

HEY, guess what, Art Bell is back on the radio.
Back to the weird old days.

[Cygnus X1]

Old cap formed ok...
Got 440 VDC off the rectifier, and the cap, etc.
Connected the output transformer, and nothing.

The OT is shorted.

Ordered a couple of caps, and an OT. On sale for 435.00 at Triode Electronics.
J/K. Tranny was around 20 dollars and we'll see how those caps do.
No point in getting the original style can cap. It's a waste of money.

[fett]

The will be the first model Magna-cyg $$$ ever made.:ROTF:

[Cygnus X1]

A picture of the subbed-in capacitor:

[Cygnus X1]

I like to bolt these caps in, where possible.
Even after it's unplugged, there's still a healthy 440 volts and
enough current to say "Momma" if you touch it. I bleed it down
with a 4 watt resistor to ground just to be safe when discharging it.
Even a little 5 watt amp needs a lot of juice to make the tubes happy.

Edit: I was looking at the original posts in this thread. They didn't put a choke in this amp.
Not too shocking, it's a hybrid of the original 5C mixed with a bit of 5F Fender Champ
circuitry in it. And the first assessment was right, tranny shot, big cap is toast (A lot of that "rust" is actually cap guts that leaked all over the chassis), but there is good news. It looks like the Power Tranny survived. That's the high dollar part. I won't really know for sure until it gets a full load, and if she gets real warm, it may be an issue.

But, the amp is well worth it. Google it. Magna Varsity 108. I haven't found any, yet, to speak of. This is even more point to point wired that the obscenely high dollar Fender Champs. That's some serious Mojo, in the truest sense of the expression.

[SEEGERMANY]

I foresee a future post from fett stating that his trailer burned down and investigators have determined it was due to the meltdown of some prehistoric guitar amp.

[guitarsjb]

I foresee a future post from fett stating that his trailer burned down and investigators have determined it was due to the meltdown of some prehistoric guitar amp.

:ROTF:Now, that's some funny shit there!:ROTF:

[Cygnus X1]

I foresee a future post from fett stating that his trailer burned down and investigators have determined it was due to the meltdown of some prehistoric guitar amp.

Thanks for the support, SG.

[SEEGERMANY]

Thanks for the support, SG.

Humor my friend, humor.

[SEEGERMANY]

Funny thing is, one of those exploded on my bench for a completely different reason. Don't ask, it was a learning experience.

(Ok, since you asked)...
There's a series of ahem, low value LARGE voltage caps in the power section. I replaced those four, got one backwards, and this D-Cell sized
cap exploded and puked it's guts all over the amp. That was right before it burned through the diodes. WTF? what was the fuse doing? Oh, that's right...they don't PLAN on someone putting a cap in backwards.

Just so you know, much of my humor comes from what you guys supply.