Theory behind this power supply?

[1blueheron]

I assume there are a couple errors here but want to know what the experts say. 

It looks to me like they mis-identified pins 4 and 6 as pins 3&5?  The voltage reference chart is not in agreement with the schematic and I am not aware of any 5U4 tubes using pins 3&5. 

The next thing I don't completely understand. Is the B+ voltage coming off the center tap of the 5V secondary? How does this work?

[Bieworm]

you didn't post any document of what you're asking.
but if I understand what you're saying about the pinouts... I attach the wires to pin 7 and 5 (both unused pins) and from there I put a 1N4007 protection diode from pin 7 to 6 and from 5 to 4.

Better read RobRob's page about this: https://robrobinette.com/How_Tubes_Work.htm

The 5U4 has no real heater. It are the cathodes that get directly heated by the 5VAC power supply secondary. Those cathodes carry the rectified DC voltage that you use to power the B+ line. Also, there is no center tap on de 5VAC wiring.

[1blueheron]

Sorry.  Fixed it.

[Willabe]

It looks to me like they mis-identified pins 4 and 6 as pins 3&5?  The voltage reference chart is not in agreement with the schematic and I am not aware of any 5U4 tubes using pins 3&5.

Yes, should be pins 4 and 6.

Is the B+ voltage coming off the center tap of the 5V secondary? How does this work?

Yes, the B+ is taken from the 5v CT.

There is no ground reference on the 5v rectifier wind, it floats. That secondary is just a wind of wire, like a choke. But this 5v secondary has a CT. So taking the B+ from the 5v CT, that wind acts like a choke.

Im not sure, but I think on a 5v or 6v heater secondary they wind it with a heavy gauge wire with only a few turns? If so, that would not give much induction, so very low Henri's, mH's? A choke is wound with a thinner gauge wire, more turns, more induction = Henri's, not mH's? 

We've had a few guys who had a 5v heater wind with a CT and who tried wiring it both ways, taking the B+ from pin 8 of the rectifier tube and then taking the B+ from the 5v CT. They heard no difference in noise. They were using a GZ34/5AR4 rectifier tube. 

But, I've read recently, where they say that you'll only hear a difference with a directly heated rectifier tube, ie, 5U4, 5Y3.

That said, I'm not sure there's enough induction/Henri's to make any noticeable difference in noise? Although, it can't hurt anything. If I had a PT with a heater CT, I'd use it.   

Also, there is no center tap on de 5VAC wiring.

Some PT 5v secondaries do have a CT. Hammond has a number of them. It's an old Hi-Fi thing.

[pdf64]

With directly heater cathodes, taking the rectified DC output from the heater CT should act to avoid the 5V from contaminating it.
But with an indirectly heated cathode, doing that may be theoretically detrimental, adding 2.5VAC on to the DC output.  Rather the DC output should be drawn from the cathode pin.

[PRR]

In theory, taking one end of the rectifier filament adds a few volts AC to the pulsating DC we want. Taking the other end just changes the phase of the unwanted AC. A center-tap makes the best output.

In practice, at g-amp voltages, the difference is almost invisible.

Induction is low, and also nulled-out in the DC path?

In very simple gear, it makes a neat simple layout. Yes "it looks like the DC comes out of the PT" but you get over that.

I think PT makers used to under-charge for added taps. It saved the radio/amplifier builders a wire. When the winders got rational, builders decided they could wire it cheaper than paying the winder to tap. In mass-market goods a rectifier CT has not been common since the 1940s?

This is an example of hot-switching B+ in a commercial product. (The relay in the B return.) And if I understand it, it might be hot-switched many times a day for intercom use. We don't know if it is a good example, or if the builder got paid to replace those rectifiers a lot.

[1blueheron]

Thanks to the THT braintrust for unraveling this mystery for me and teaching me something of value in the process.  I have been scratching my head for a while thinking I am witnessing a supernatural phenomenon of spontaneous high voltage generation from a 5VAC secondary.   I am still a little foggy on how the wires can be low voltage AC and high voltage DC at the same time, but at least I know I am not crazy and it does work as drawn and has a solid working theory behind it. 

[shooter]

little foggy on how the wires can be low voltage AC and high voltage DC at the same time

think of AC as lazy, it'll hitch a ride on any DC potential.  or;


surf up understanding AC theory.....understanding AC transmission........Riding AC on a DC potential
the complex, long winded explanations are always fun

[Willabe]

..... I am still a little foggy on how the wires can be low voltage AC and high voltage DC at the same time, ......

Every tube is fed dcv to it's plate and it outputs acv. That's why there is a blocking cap inbetween the plates output and the next stage, to block the dcv and let the acv signal pass through to the next stage.

The OT blocks the dcv on the primary from the secondary and lets the acv signal pass through induction.

[PRR]

> how the wires can be low voltage AC and high voltage DC at the same time

Go to the beach.

There is a long-term water level, the DC.

There are short-term wind waves, fast AC.

There may even be long-term waves, tides, a different AC.

[1blueheron]

Got it!