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In Reply to: RE: ok, what is happening here???? posted by Triode_Kingdom on December 03, 2016 at 13:58:37
I must have missed that the first time around. Thanks for the heads up. I will have to check and see what the amp rating is on these little puppies, but I think they could handle two 813 filaments anyway. I will post pics when I get some results. Thanks.
Follow Ups:
"I think they could handle two 813 filaments anyway."
It will handle a million of them if you wire them in SERIES. That's what I said to do - two or three in SERIES.
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Buy Chinese. Bury freedom.
Think I will just go with one since that is the way I intended to use them anyway.
You must have misunderstood my post. This was only for the purpose of temporarily loading the transformer so you can test it again. You can't simply hook one tube to the transformer; the voltage is too high. So, you can do what I suggested or you can buy a HUGE power resistor.
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Buy Chinese. Bury freedom.
Edits: 12/03/16
I was planning on using my variac and just taking it up until I get to 10 volts for now. By seeing at what percetage of full power I get to 10 volts at if will give a fair idea of what volts will be at full power. Good enough for now, and will give me some idea of how many volts I am going to have to drop.
I think Triode Kingdom hits the nail. Reducing the input voltage will most likely reduce the DC pluse frequency instead of the output voltage for these type of chopper transformers.
I don't think it will sound the best also at the reduced DC pulse. Why not use a regular 12V SMPS power supplies and reduce the output down to near 10V? I have experienced with them and found they work quite well for the 10V filaments in the Big Transmitter tubes.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
I wasn't suggesting a permanent reduction, just a temp one. Doesn't sound like it will work anyway. I am already using smps units on one channel, wanted to try AC on the other to see what difference there might be in the sound.
The units I initially used measured close to 24V pk-pk. At that voltage, nothing too exotic was required in terms of dropping resistors to reduce it to 10V. At 33-34V, that's no longer true. You would need total resistance of about 1.2 ohms and 30W dissipation capability. Do your units have toroidal output transformers, or are they conventional like the ones I purchased? The former would be easy to modify.
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Buy Chinese. Bury freedom.
I actually never checked, but I will. I really want to see if I can hear the AC "difference" in the sound of the amp though. That will be the deciding factor for me, all other things being equal.
"Why not use a regular 12V SMPS power supplies and reduce the output down to near 10V?"
The goal is to heat with AC at an ultrasonic frequency. Quite a few enthusiasts, myself included, have found that AC sounds better than DC heating.
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Buy Chinese. Bury freedom.
Well then, you're in uncharted territory. I doubt the reduction in output voltage is a linear relationship to the input. These oscillators work by means of a saturable core transformer. They don't behave at all like coupled inductors. I hope you have some junk 813s you can sacrifice for this experiment.
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Buy Chinese. Bury freedom.
Well there goes that plan. Now, where did I put that big freakin' resistor?
But how did the 12sn7 filament I had hooked to it survive?
Well, most filaments don't usually burnt out right away even at the higher voltages. Even if the filament doesn't burnt out, you just accelerated the aging of the heater / cathode and the emissions. The heater / cathode may never burnt out even at higher voltages but actually shorten the tube life.
12SN7 heater work fine with 12V so it may be just fine.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
If what everyone is saying is correct, it actually had 15 vac on it for a while.
I suspect you find find it simpler to have each 813 have its own supply.
ray
Me too.
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