Can I put a tube rectifier after a PT that ain't center tapped? (6x4 -> Epi Valve Jr)

[Iplayloud]

I think not, right ? The thing is I want to add a 6X4 rectifier in a Epiphone Valve Jr. If all I want is the tube sag, I could just sent the rectified voltage after the diode bridge, split to both anodes of the 6X4 and bingo right? Thx!

[Bruce / Mission Amps]

If the transformer does not have a center tap then you need a FWB, full wave bridge rectifier... tube rectifiers are a full wave rectifier.
All you'd need to do is use two 1N4007 diodes with their anodes grounded as the other two diodes and use the 6X4 as the forward diodes.

[Iplayloud]

Alright thanks, with this configuration do I get only 50% of the voltage drop and sag or 100% ?

[R.G.]

If you make a diode bridge out of one tube rectifier for the positive side and two 1N4007s or similar for the other side, you will get the same voltage you used to get with solid state diodes, minus whatever is lost in the tube rectifier's forward drop. The tube rectifier will conduct on alternate half cycles, so it should give you about the same sag as you'd get from it running from a centertapped winding.

What you won't get is any sag from the higher resistance of a center tapped winding, so it will have a bit less sag than a CT circuit, for reasons having nothing to do with the tube rectifier.

And if you put a power resistor in series with a SS full wave bridge, you will get a remarkably good emulation of what a tube rectifier would do.

[Enzo]

But how about his original question? Make a solid state bridge, then feed the resulting DC THROUGH a tube rectifier - a series sag element.

[Jazz P Bass]

Huh!

[Enzo]

Is that a good Huh! or a bad Huh!?

[Steve Conner]

I'd be most worried about the heater supply for the 6X4. The Valve Jr PT wasn't designed for the extra load.

Also the 6X4 was designed to run off the same heater supply as the other tubes and stand the full B+ voltage across its heater-cathode insulation. They can short out spectacularly. Maybe you could insert it in the negative DC output of the bridge, so the anodes would be grounded and the cathode would be almost at ground potential.

[Alex R]

... also I'm not sure it's a good idea to have the rectifier heater on the same winding as the other heaters, given the propensity of rectifiers to short plate to heater. I've seen a lot of damage in old AC10s caused that way.

[Jazz P Bass]

Is that a good Huh! or a bad Huh!?

That is a good 'Huh!'

[potatofarmer]

This seems like an awful lot of trouble for a single-ended amp. Have you tried a resistor first to see if you like the voltage drop? It's class A so you're not going to get any appreciable sag when playing.

[Steve Conner]

Good point. A class-A single ended amp draws virtually the same supply current at idle as cranked flat out.

[J M Fahey]

But a ceramic resistor does not glow in the dark nor is encased in glass.

[potatofarmer]

Well, you could get crazy with some nichrome wire and an old light bulb...

[Leo_Gnardo]

But a ceramic resistor does not glow in the dark nor is encased in glass.

Well, we can arrange things so it does, and even will make its own glass coating Sometimes that happens even without "intervention."