811 heater power supply...

[Rod Coleman]

What is the filament tolerance for directly heated tubes? I recall indirectly heated is +/- 10% so you would be spec there.

It's +/- 5% for any Filament (i.e. Directly Heated Tubes). You can verify this from many RCA data sheets, among others.

This is a challenge for unregulated supplies, given that mains tolerance is as bad as +/-10% in many locations - including here in the UK. Yes, the allowable range was actually degraded here, recently.

The tube lifetime is strongly affected outside of the +/- 5% range, and even +5% is unnecessarily stressful for an expensive DHT - adding suitable regulation will pay for itself, in such cases.

 

[knockbill]

I just happen to be building a high current supply myself, so.. What I suggested may be more difficult but can make for a good supply. The chokes provide reactance required for the filtering with less resistance than it would take for that kind of filtering using resistors alone.

In addition, the second one might assist in isolating the supply from your filaments to reduce signal currents going through the supply.

BTW this supply isn't for filaments but I do my filaments this way as well. I needed to wind one of the chokes, and they're not small.. but I'm happy with the result.

I ended up using two separate 10A FTs, with a 25A 50V bridge, and 2 x 22000uF caps on each one... A 0.2 to 0.5 resistor, or small inductor between teh caps allows 6.3-6.4VDC, depending on the tube used...

 

[knockbill]

Here's a couple pics of the amp...
Thanks for teh PS info...