Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: spunko on March 02, 2025, 10:22:34 pm
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Hello, this amp came making some weird noises and cracks, V3 was the problem. New tube and the amp is dead quiet.
What have caught my eye is the rectifier 5v winding, has only one yellow wire. First time for me, is it center taped? is this normal? The amp works great tho, voltages are up to spec.
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I don't get it either
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Once in there, I installed back up diodes for the rectifier. Took readings again and all voltages are to spec.
If I measure AC on the yellow wire reference to gorund, it gives 5vac
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What is that blue wire? That may be the other end of the heater just run to the board and connected to the gray wire through a fuse--and the two colors are to differentiate board vs socket termination.
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Please post a photo that shows where all the wires actually go.
But you're right, that doesn't look "normal." On the other hand, if it ain't broke . . .
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the '65 DRRI? Got a schematic?
Check that the other yellow wire is in the circuit somewhere (like to the B+ filter cap). The 5V winding has to have both ends connected (in some way) to the rectifier filament.
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+1 Tubeswell
??If I measure AC on the yellow wire reference to gorund, it gives 5vac
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The 5V AC Heater winding MUST BE floating and ISOLATED from Ground :laugh: (or Fireworks inside transformer :l2:)
So the only real measurement that can be performed is AC Volts across pins 2,8 on Rectifier I believe.
Regards
Mirek
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maybe they just ran out of yellow wire that day at the plant.. :dontknow: in jest
we need to see more of the guts to tell what's going on as acheld has mentioned.. please post more pics thanks
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The PRRI has a fuse (located on the main board) in the 5V filament winding. Maybe Fender decided to fuse the 5V winding in later DRRI circuits too. Although I can't find a schematic for the DRRI that shows such a fuse.
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The PRRI has a fuse (located on the main board) in the 5V filament winding. Maybe Fender decided to fuse the 5V winding in later DRRI circuits too. Although I can't find a schematic for the DRRI that shows such a fuse.
Yes. Working on one of those is what gave me the idea that the blue wire runs to the board, through a fuse, then meets with a trace coming off the other end of the gray wire.
I bypassed the board mounted fuse on my PRRI and had to do a bit of board tracing. I'd also heard that Fender is fusing all secondaries in order to comply with EU regs.
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OK, so those light blue wires are the heater circuit. Even though the "shchematic" says they should be green.
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Well they're sort of bluish green ,, what a mess on that power tube socket. Last time I saw one of those boards was when I gutted it and replaced it with an AB763 turret board - Alessandro style.. interestingly people buy the used Fender pcbs.
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.... replaced it with an AB763 turret board - Alessandro style..
What is "Alessandro style"?
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Come on Willabe. :laugh:
https://alessandro-products.com/rewiring-services/ (https://alessandro-products.com/rewiring-services/)
If you read this above page you could get caught up with a little corksniffing ( :huh: )
I believe we all do nice builds with our turret boards and some of our colleagues have a VERY high standard (neat wiring and component placement).
I also believe Doug's Boards rate very highly.
Kind regards
Mirek
EDIT: Fixed broken link -- HBP
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I didn't know he did reissue rebuilds. :dontknow: I do know he makes great speakers with Eminence speakers.
I couldn't get the link open, this link should work;
Hand-wired Service – Alessandro Products (https://alessandro-products.com/rewiring-services/)
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Sorry Willabe,
I couldn't open it either :dontknow:
BUT if I cut and paste it into a blank Google session, it works :w2:
Your link works fine as well (here in Aussie)
Regards
Mirek
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Doing a conversion of a reissue like a DRRI using a Hoffman board is pretty easy too. And the filter caps can all mount on the board. I make the board a tad wider to accomodate mounting the preamp filter caps behind the pots. The existing DRRI bias pot is easily wired into the board. I make my own boards to suit.
If you search ebay you'll find Allesadro selling reissue pulls.. His business has been doing it for a long time now.
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Here are two links to Allesandro selling on ebay..
https://www.ebay.com/itm/275460236385 (https://www.ebay.com/itm/275460236385) the conversion service
https://www.ebay.com/itm/286244281054 (https://www.ebay.com/itm/286244281054) a PRRI pull
oh and notice he has what looks like his own company branded F&T electrolytic caps.. or look alikes I think they're F&T made..
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BUT if I cut and paste it into a blank Google session, it works :w2:
I save it into favorites, then copy that link and post it here. Then I delete it from favorites.
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..... links to Allesandro selling on ebay..
https://www.ebay.com/itm/275460236385 (https://www.ebay.com/itm/275460236385) the conversion service....
He used Fenders layout. :think1:
I wonder what he charges?
oh and notice he has what looks like his own company branded F&T electrolytic caps.. or look alikes I think they're F&T made..
That probably just means he has enough $$ to have someone do a run with his name on the label.
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I'm sorry, I couldn't take the full pic, the amp was needed super fast. It was gone the moment I posted this question. :sad2:
What I recall is seeing a thru-hole 5 amp fuse (maybe 5A?), those that look like a green vishay resistor. First time seeing it in this amp DRRI, and is not found in the google schematics I have downloaded.
Also that blue wire went to the PCB and I haven't seen it in previous amps.
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Willabe the cost was right there on the ebay page $650 for a conversion.
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Willabe the cost was right there on the ebay page $650 for a conversion.
I didn't understand that. I thought it was a guy selling an amp he had Allesandro rewire for him. I see now it's Allesandro selling just the rewire upgrade.
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Sorry Willabe,
I couldn't open it either :dontknow:
BUT if I cut and paste it into a blank Google session, it works :w2:
The "URL" tags were replaced with tags for FTP.
When you instead dropped the address with "no protocol" in your browser, the browser figures out it should be HTTPS & redirects you.