Crate VC 6210 power supply problem

[jvm]

I ahve a Crate VC 6210 with a open power transformer primary. Mercury makes a replacement but really can't put almost $200 into a PT for this amp. I have installed a PT for a Hot Rod Deville. I am aware that my low voltage winding is too high but I will deal with that later. My problem is that I am only getting 42 vdc B+. My high voltage secondary shows 368vac with no load. Schematic shows 470VDC at plates. 470/1.4=335v for the required secondary voltage. I have replaced all filter caps, all rectifiers in B+ supply. All four 56K resistors test good. I lifted R94 to eliminate any possible issue with bias supply. I am testing with no tubes installed and output transformer primary disconnected. Any ideas as to why I'm only getting 42 VDC at my plates? Crate VC60 (2) (1).pdf

[52 Bill]

The Crate schematic doesn't show one, but in order for that power supply to work, there needs to be a center tap on the high tension secondary. Does the HT winding have three wires or just two?

Is it possible that the transformer has the HT center tap connected internally to the center tap of the low voltage winding? If you still have the original one, see if there is any continuity from the HT winding to the low voltage winding.

You will need to go to a full wave bridge rectifier to use the Fender transformer.

[jvm]

You nailed it , 52 Bill! I have continuity between the HV winding and LV center tap on the original Power transformer. Time to rearrange some diodes! Thanks!

[FATHEROFFOUR55]

Hello Gentlemen!

I am of interest in doing the same tranny "swap" in my own VC amp.(with a failed power transformer)
is it, that the circuit in this amp is only using a half wave rectification instead of a full wave rectifier?
while I do know how a bridge rectifier looks,
I wonder if you would not mind drawing a simple diagram of how you "rearranged" the diodes to fit this circuit?
yes, i do have some inkling of possibly doing it myself,
although I would much rather be sure of a better outcome by hearing of a successful mod/repair than to try to possibly fail or get stuck on.

thank you.

[SoulFetish]

Hello Gentlemen!

I am of interest in doing the same tranny "swap" in my own VC amp.(with a failed power transformer)
is it, that the circuit in this amp is only using a half wave rectification instead of a full wave rectifier?
while I do know how a bridge rectifier looks,
I wonder if you would not mind drawing a simple diagram of how you "rearranged" the diodes to fit this circuit?
yes, i do have some inkling of possibly doing it myself,
although I would much rather be sure of a better outcome by hearing of a successful mod/repair than to try to possibly fail or get stuck on.

thank you.

If your not familiar with working on tube amplifiers you should be extremely cautious because you'll be exposed to lethal voltages. Having said that, this amplifier uses a Two Phase rectifier in the high voltage secondary. You can read about rectifiers here:
The Valve Wizard

[FATHEROFFOUR55]

Thank you Soulfetish!

If your not familiar with working on tube amplifiers you should be extremely cautious because you'll be exposed to lethal voltages. Having said that, this amplifier uses a Two Phase rectifier in the high voltage secondary. You can read about rectifiers here:
The Valve Wizard

Thank you soulfetish!
I apologize for the late reply, and i so very appreciate the useful information in the link that you sent me.
it will come in very handy for sure.
and, I actually do have a some experience with tube amplifiers. and of other circuits and electrical devices.
I have repaired and modified tube and solid state amps with varying success over the years. (often borrowing and copying other circuit designs) and yes, i have also had the crap shocked out of me early on from a transformer. but, as some people here and elsewhere, i have more experience in some areas of electronics, but am weak or much less experienced or less knowledge in other areas.
i do have somewhat basic idea of what a rectifier does. many years ago,(as a teen) my first experience was helping my dad fix a 12v power supply that the transformer went south but took the rectifier with it.
my dad had some of the parts around, but he had to order a new bridge rectifier for it. I had no idea of what one did back then after he explained it, I learned a little about converting AC to DC and how the now converted 12 volts had to be rectified to be useful to running the DC powered car stereo that I was planning to use it with. (as sort of a beginners bedroom stereo)

the problem I have here,
is that I do not understand the full reason (or the difference) for the center tapped transformer in regards to the type of rectification that is needed.(half wave, full wave,??) the amp I am repairing is mostly on a circuit board as opposed to point to point wiring that i am more familiar with,(and seemingly made more complex or confusing because of the board) and I was curious how the other member achieved the modification and had hoped for a diagram or even a photo could be included in his reply (if, he replied at all)

but please know that I am grateful for your reply and the information supplied in the link. I guess that by just knowing that he was able to convert his amp to use a different transformer, I should at least study up on the related components and attempt to figure it out myself and not sit and wait for someone to do it for me.
thanks again and I really appreciate it.

[SoulFetish]

the problem I have here,
is that I do not understand the full reason (or the difference) for the center tapped transformer in regards to the type of rectification that is needed.(half wave, full wave,??) the amp I am repairing is mostly on a circuit board as opposed to point to point wiring that i am more familiar with,(and seemingly made more complex or confusing because of the board) and I was curious how the other member achieved the modification and had hoped for a diagram or even a photo could be....

Quickly, the use of center tapped Transformers in tube amps is partly historic due to commonly used tube rectifiers. But they offer some benifits as well, like the ability to generate a negative voltage...( this sounds familiar, i'm probably plagiarizing Merlin right now. This is probably on his site). But i would post this question in the Theory and design section, as there are people more qualified and I, who can explain power supply design in a clear fashion. Plus, its a nightmare trying to get into an explanation like that when typing on my phone.
Good luck.