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In Reply to: RE: what kind of builder posted by RayP on January 20, 2017 at 06:03:34
Ray which halo lighting transformer you can who heartily recomend for the gm70??
please include a link or where to purchase please
I would like to experiment with something else besides rod's regulators
the regulators are excellent but man there is some much added crap I would like to simplify it some
Lawrence
Follow Ups:
You can see how I got roughly 20 vac here in the attached link and what I used.
Remember that my amp is just a think piece trying out technologies and ideas that would reduce weight. It sounds very good on well recorded pieces with incredible detail. However, it can sound quite shrill on less well recorded pieces. Tracking down what is causing what has been a matter of trial and error, but it has been fun.
From past experience with a line stage, the detail comes from using the 6S17K-V input tube. I think the shrillness comes from my implementation of the high voltage from the 48 vdc smps units. Shielding helped as well as using some capacitors, but I think I have more work to do.
As to the halogen units, I doubt that they affect the sound all that much compared to the other issues going on in my amp. In any event, try them and see if they work for you. They certainly are cheap enough.
ray
Thanks Ray I ordered them units that defbykhorns suggested and there wont be much time to wait because there right here in the states :)
If these sound as good as the colmen regs I will be tickled pink
Lawrence
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.
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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