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In Reply to: RE: what kind of builder posted by used-hifi on January 20, 2017 at 16:12:05
Add 5 turns to the output toroidal and you get 20volts
These have been tested and work well
I have tried both the Coleman and the Ultrasonic, i could flip a coin on either one but the halo is much easier to implement.
Follow Ups:
Can these be used with tubes requiring 6V and 3amps? If so, how would the voltage be adjusted down to 6V? Resistor?
yes you could use a resistor but totally not the best idea just unwind some off of the torroid and measure under load until you get desired voltage
Lawrence
You will need the 220v at 120 input supply to get that low
Well that is very interesting and I thank you for comparing both methods. Somehow I suspect using high frequency AC will now become quite common for directly heated tubes.
ray
Ray are you biasing the gm71 tube at 95ma?
if so what would be the life expectancy? I am curious to bias my gm70 there also
Lawrence
So far I have kept the current at less than 100 ma. It's easy to adjust using the Powerdrive circuit and the main limitation is what current your output transformer can handle.
The GK71 pentode has a plate dissipation of 125 watts and 576 volts times 95 ma is only 55 watts. I suspect some would suggest that I raise either VDC and / or current to get more power, but I don't need to.
ray
I just adjusted mine LOL took some of the led's out in series now biasing 97.5ma about 119watts plate dissipation
you can hear an improvement it just sounds better to my ears
this is why I love breadboards :)
now the question would be how many hours will the gm70 tube last at this dissipation???
Lawrence
Ray we shall see I have an optimized rod colman heater setup here with common mode torroid choke 124mv ac going into the colman regulator its down into Uv range on the output, well see if it compares
alot of my amplifier is NON conventional that works very well so this happens to be up my alley
Lawrence
Thank you very much!!! I will order right now
Lawrence
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