Another DC Heater Question?

[big_teee]

I'm interested in DC Heaters.
I found a Schematic of the new VHT Special 6 Ultra.
They use AC heaters for the 6V6 Amp tube.
Then they convert the 6 VAC to DC With a diode Bridge.
I understand the DC part except for the LED D5 in the heater circuit.
The Schematic is at the end of the Owners Manual.
http://www.vhtamp.com/manuals/VHT-Sp...tra-Manual.pdf
Thanks for explaining in advance.
Terry

[Wombaticus]

I'm interested in DC Heaters.
I found a Schematic of the new VHT Special 6 Ultra.
They use AC heaters for the 6V6 Amp tube.
Then they convert the 6 VAC to DC With a diode Bridge.
I understand the DC part except for the LED D5 in the heater circuit.
The Schematic is at the end of the Owners Manual.
http://www.vhtamp.com/manuals/VHT-Sp...tra-Manual.pdf
Thanks for explaining in advance.
Terry

D5 appears to be the power indicator lamp.

[big_teee]

D5 appears to be the power indicator lamp.

Ok.
Then you have to have F1 & F2 Fuses to get a pilot light.
I'm used to a pilot right off the AC.
What is the purpose of RT1 on the Primary side of the PT.
Looks like they went big on fuses and Other Protective devices.
Thanks,
Terry

[Wombaticus]

Ok.
Then you have to have F1 & F2 Fuses to get a pilot light.
I'm used to a pilot right off the AC.
What is the purpose of RT1 on the Primary side of the PT.
Looks like they went big on fuses and Other Protective devices.
Thanks,
Terry

It's a negative temperature coefficient thermistor. Gives the PSU a soft start by limiting current until it gradually warms up.

[big_teee]

Does the DC Heater portion appear to be a Hum free Circuit?
The DC portion for V1 & V2 Looks pretty straight forward and could be put on a small eyelet or Turret board.
Don't know what the physical size of the Filtering cap would be, but it could be a low voltage Cap.
That's quite a little amp.
Thanks again.
Terry

[Wombaticus]

Does the DC Heater portion appear to be a Hum free Circuit?
The DC portion for V1 & V2 Looks pretty straight forward and could be put on a small eyelet or Turret board.
Don't know what the physical size of the Filtering cap would be, but it could be a low voltage Cap.
That's quite a little amp.
Thanks again.
Terry

Honestly, it's kind of a marginal DC heater circuit. I'd be more comfortable doing this for just one tube. For one thing, unless you use Schottky diodes, I don't see how you're going to get more than about 5.9-6.0V out of it. If you do this, be aware that:

1. You need a low ESR / high ripple cap;
2. The power factor will be crap, and you'll need to budget ~8VA of capacity in your trafo for those two tubes alone;
3. The diode bridge needs to have significant current handling ratings.