477v after 5Y3 SF Vibro Champ

[phalanges]

Kinda hot .
What are my options?

[ampgeek]

With or without the rest of the tubes installed?

If without (and everything else seems to be OK) slap the other tubes in and see what you get.

Good luck,
Dave O.

[phalanges]

With tubes.
But the circuit has been butchered and I want to bring it back to stock.
I saw that all the B+ measured high and measured 477v at the 1st node.
Figured I should get the PS voltage in line first. ?
Thanks for the reply.

[Colossal]

Yikes man, that's toasty.

Pull the rectifier, power it up, and measure the AC on the PT (pins 4 and 6 of the rectifier socket). Start there and report back.

[ampgeek]

Also check if the filter cap can was replaced during the hacking. It might get beat about the head and shoulders during the trouble shooting process!

That voltage isn't too far above what I saw in the early 70's SFVC sitting on my bench right now (waiting for a fucking speaker to finish it off!!) with all but the recto pulled. So...I am guessing that some/all of the tubes are not conducting.

Check all tube grounding paths closely for continuity if you can.

And...if you get it back up and going....be prepared for a treat. The one in front of me sounds better than any Fender SF amps has a right to through my 12", closed back speaker cab loaded with a Scumback! I was stunned to tell the truth. My understanding is that it's DNA hasn't changed much from the BF versions though.

Good luck!
Dave O.

[morcey2]

Check the rectifier and make sure it's not a sovtek "5Y3GT." They're nothing like a real 5Y3 and don't drop much in the way of voltage the way a real one does. If it is the sovtek version, get a real one. They're not too expensive and JJ started making one that I've heard is a real 5Y3.

(totally OT. I drop out of amp building and someone finally starts making a real 5Y3. That was one of my biggest complaints a couple of years ago.)

On top of that, if your wall voltage is much above 115, you may want to look into adding a bucking transformer or something to get it down to the 115 range.

Matt

[statorvane]

JOOC what are your heater voltages measuring?

[echuta13]

Most of these amps had some crazy hi voltages (silverface era especially). The funny thing is that Fender never bothered to rebias the output section of these vermints (running WAY out of spec).
As Matt stated... make sure you have a real 5Y3 in there (about a 50v drop vs. SS rectifier)

[phalanges]

Thanks, everyone for responding.
Seems there are different schematics with different voltages in books and on the web and I have one that calls for 355v at the 1st node.
Today, with an experienced tech, I went over a schematic from Pittman's book that called for 420v and the tech said that the over voltage could easily be attributed to higher wall voltage.
At any rate, I feel that I can move forward with the existing PT and chassis.
All else is questionable.
When I post a gut shot you'll crack up though I'm sure you've all seen worse.

[morcey2]

When I post a gut shot you'll crack up though I'm sure you've all seen worse.

We've all probably _done_ worse.