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Trouble shooting silicon rectifier diodes in power supply.

What are the other diodes for on the heater center tap? The voltage on them kind of swing a volt to a volt in a half except the center one was sready.
 
There may be an error in the diagram; either it shows
the bridge and the two isolation diodes suggested by @gadget73, or two rectifier bridges in parallel; in some Grommes amplifiers, you’ll find tube rectifiers connected in parallel—were they trying to achieve the same result with silicon diodes?
 
HowardK said:
I hooked up my black box and set the wall voltage at 106 just for peace of mind. But they still went to 425.
No tubes el84 plate right side 425 left 411.
Just preamp driver tubes right 423 left 383
Click to expand...
Thanks! For sure, the problem lies in the power supply.

HowardK said:
I wonder why he changed the diodes to uf4007 from what's in the first addition like mine which I don't know what's in there.
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Yes, that doesn't make sense, since a full-wave, four-diode UF4007 bridge rectifier is more than adequate for this SE amp.
 
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HowardK said:
What are the other diodes for on the heater center tap? The voltage on them kind of swing a volt to a volt in a half except the center one was sready.
Click to expand...
Those are 1N4762A Zener diodes. My guess is that the string is used to regulate the raised heater voltage.
 
HowardK said:
I wonder why he changed the diodes to uf4007 from what's in the first addition like mine which I don't know what's in there.
Click to expand...
UF is a fast switching diode, generally intended for high frequency switching type applications. Some assert there is an improvment in PS noise using them instead of "slow" diodes like 1N.

Again though, they still serve the same basic function if they're working as diodes.
 
5dc87ef8-088a-48e9-86a6-46ce9d70183e.jpg


You know, this could work. There would be a lot fewer parts to deal with.

Just an idea. :idea:
 
Redrew the diodes in LTSpice in the same layout as hand drawn in post 1, and get same results as when drawn more like the schematic / post 64.

So, on presumption it's all wired like that, the arrangement of the diodes in itself isn't the problem.

1787800759008.png
 
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yeah I don't think its a design problem, but a failed component problem. The current being low in the low voltage channel makes me think its supply side, not load-side. One open diode or bad first cap would be my first two thoughts there.

current being high in the high voltage channel may also be a failed component, but probably load-side in that case, so ultimately I think we're looking at multiple problems here.
 
gadget73 said:
yeah I don't think its a design problem, but a failed component problem. The current being low in the low voltage channel makes me think its supply side, not load-side. One open diode or bad first cap would be my first two thoughts there.

current being high in the high voltage channel may also be a failed component, but probably load-side in that case, so ultimately I think we're looking at multiple problems here.
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I will check the power supply capacitors.
 
I first want to think you guys for the help.
It was the first cap on the left on the power supply. Both voltages are at 403 off the diodes!
 
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