Elevated heater supplies...

Newb quesion on elevated heater supplies:

How do you do it? I got an SRPP here waiting to be tested, but the cathodes are a good 200V apart and I don't know what the best way to float my regulated DC heater supply is...

There's some transistor-based DC reference circuit in the Morgan Jones book, but I'm not sure I understand how you actually use it (plus it seems too complicated).

Is there an easy way to raise heater supplies? Using a zener somewhere, maybe?

:?

Peace,
Al.

A voltage divider off of B+ is the easiest way. The specific voltage isn't so critical; rather, you just want to keep it in the range where the heater-cathode rating is not exceeded. Since one cathode is near ground and the other is sitting at around +200V, you'll have to split the difference if you want to run them off a common heater supply. You must take into account the heater-cathode voltage of all tubes that will be running off the "elevated" heater supply.

Post some schematics and tell us the particular tubes you're planning to use.

I have seen a schematic with two seperate heater supplys, One raised and one by ground. Seperate windings on the power transformer.

That was done a lot, especially in amps with tube rectifiers. The rectifier would have its own heater winding, even if it was a 6-volt tube like the others in the circuit (e.g., 6X4).

[quote author="NewYorkDave"]A voltage divider off of B+ is the easiest way.[/quote]

Just a resistive one? where exactly do you take this reference voltage and how?

[quote author="NewYorkDave"]The specific voltage isn't so critical; rather, you just want to keep it in the range where the heater-cathode rating is not exceeded.[/quote]

I understand the need for elevated power supplies, it's just how to actually make one in practice that has me scratching my head! :?

The tubes are some russian 6N1P with Vhk spec'd at 150V, which is borderline with my B+ (310V, ~150V quiescent on each tube). I figure raising the heater supply by ~70-80V would work... just can't figure out how to do it cleanly, cheaply and easily.

Peace,
Al.

So let me get this straight: it's a single 6N1P with the two triodes used in series. The plate of the upper triode sits at about 300V, and the upper triode cathode/lower triode plate sits at about 150V, and the lower triode cathode sits a couple of volts above ground. Is this correct?

How is your regulated heater supply derived?

Schematics would make this a lot easier.

[quote author="NewYorkDave"]a single 6N1P with the two triodes used in series. The plate of the upper triode sits at about 300V, and the upper triode cathode/lower triode plate sits at about 150V, and the lower triode cathode sits a couple of volts above ground. Is this correct?[/quote]

That's exactly right!

[quote author="NewYorkDave"]How is your regulated heater supply derived?[/quote]

With a good ol' 337 voltage regulator.

[quote author="NewYorkDave"]Schematics would make this a lot easier.[/quote]

I know... But my scanner died on me and I have no way of drawing the circuit in this computer

Peace,
Al.

[quote author="alk509"]With a good ol' 337 voltage regulator.[/quote]

That doesn't tell me much, although it'a odd that you're using a negative voltage regulator. (Did you mean 317?).

If you want to "float" that supply, it must not already have a ground reference. Is it derived from a separate transformer, or a dedicated heater winding on the main transformer? What's the rectification--full wave bridge?

In e.g. the pultec, the heater is rised 55V above ground:

http://www.gyraf.dk/gy_pd/pultec/pultech.gif

It's as simple as that...

Thanks, Jakob, that's a perfect example of what I was talking about.

Since the heater circuit isn't drawing any current through the voltage divider--which is just providing a reference for the heater to "sit on"--the resistors in the voltage divider can be fairly high in value, to avoid drawing current unnecessarily from the plate supply.

Al's case is a little bit more involved since he wants to float a regulated DC supply, not AC.

Assuming you meant LM317, and you want an +80V reference, consider this:

Notice that neither side of the heater circuit is grounded.

I did mean a 317. Thanks Dave and Jakob! You are the shit! :thumb:

And no worries: I built my heater PSU in a plastic box with no connection to any external grounds, so I could float it when prototyping.

Peace,
Al.

People who live outside the US, or who are over 30 years of age, are probably wondering "Why on earth is he calling them shit?"

But I know what you meant. You meant "da schizznit." :wink:

> consider this:

No real reason to have the 100+100 resistors across the output.

With an AC supply, that keeps the middle of the AC steady for less AC radiation. But with DC, there should be no problem. Just tie any handy point around the 6VDC side to a 55V reference.

The reference should be pretty high resistance. Ideally the heater insulation is "infinite" so no current flows. If insulation breaks down, a high resistance bias limits the current flow. Few-dozen-Kohms is a good ballpark.

Works great, thank you guys!

I love this place :green:.

Peace,
Al.