Strange rectifier configuration - Vibrolux Frankenstein

Working on a Frankenstein amp (Vibrolux 5E11 - kinda). It has the strangest wiring of the PSU that I've ever seen.

The only thing I can figure is the last person wanted to use the hefty PSU transformer. 630VAC was too much, so he opted for one leg of it at around 315V.

I need some schooling on what on earth is going on here. It needs to be rewired anyway because the workmanship is shotty.

Any thoughts?

The PT supposedly has a tapping for the bias supply, as well as the two main HT taps and the CT tap - you haven't shown what is wired to all the taps (eg. CT tap, and one of the HT taps).

The rectifier base has pin 5 being used for bias supply wiring - pin 5 is not connected to the rectifier diode innards.  Look up the 5Y3 rectifier datasheet - it shows pin  6 and pin 4 as the 2 anode connections.  It was common to use spare socket pins for accessory wiring.

Okay. I think I might be onto something.

This transformer (not a Fender) does not have a bias tap. So, it appears that the B+ has been tapped and dropped for the negative bias.

But still, only one leg of the 315vac is being used.

So the CT is taken to ground?

If there are no connections to pins 4 or 6 of the rectifier base, then  I'm not sure how you are getting 260Vdc B+, or why the rectifier heater needs to be powered.

Perhaps if you start by disconnecting PT secondaries and confirming what AC voltages are on all secondary windings.

I've dissected it and will report back.

I would just guess the CT is connected to ground and rectification is single-wave, which does reduce the actual voltage by a small percentage. The bottom anode of the rectifier, being connected to a negative source is effectively disconnected.
Anyway, teh schemo does not make sense, tehre are hidden connections.

I know. It does not make sense!

I'm a'working on it.

Okay. I ripped out what was there. Here is the new plan.

Base it off the 5E11 Vibrolux circuit, but change the PSU section based on the transformer, which has a CT for the high voltage, but no secondary tap for the bias.

Any problem tapping one leg of the 310v line and dropping the value via a hefty 10k (or whatever value is required) resistor?

Like this?

And the Vibrolux, for comparison: https://cdn.shopify.com/s/files/1/2325/2729/files/Vibrolux-5E11-Schematic.pdf?5926397210715640943

(I plan to change the heaters from this original schematic from "grounded" to "virtual center tap" with resistors.)

Pin 5 should be pin 6.

Yes. Sorry. Just a typo.

How about the rest of it?

BluegrassDan said:

Any problem tapping one leg of the 310v line and dropping the value via a hefty 10k (or whatever value is required) resistor?

Like this?

Click to expand...

That's how it's done on many Amped amps. Typically, the higher resistor should be on the series leg. 100k is typical. Dissipation is about 1W.

BluegrassDan said:

Any problem tapping one leg of the 310v line and dropping the value via a hefty 10k (or whatever value is required) resistor?

Like this?

Click to expand...

That's how it's done on many Amped amps. Typically, the higher resistor should be on the series leg. 100k is typical. Dissipation is about 1W.