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Old 3rd March 2013, 07:14 PM   #1
Tom7227 is offline Tom7227  United States
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Default Newbie Tube Power Supply

I need some assistance for a Tube amplifier that I am trying to complete.

It is a stereo amp build with 6aq5 in a push pull configuration. It is driven by 12ax7's.

The issue is that the transformer I purchased has about 578 vac w/ct. I planned on using a solid state diode in a half bridge configuration, but the resultant DC voltage is 401 volts DC.

The 6aq5 does not like 400 vdc (387vdc after warm up), seems they like 250 vdc. (they get VERY hot). I don't want to change the tubes to another number.

The transformer purchased was designed to use a 5ar4 as a rectifier tube, if I incorporate that tube w/ a choke, do you think that would yield me 250- 275 vdc?

Perhaps another suggestions?

This is my first ever tube amp I am building, so please excuse my.. dumb questions
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Old 3rd March 2013, 07:41 PM   #2
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Upload the schematic you are using. Highly specific remarks are not possible without a schematic.

The fragile part in a 6AQ5 is the screen grid. As long its dissipation stays within published limits, 350 V. on the plate rates to be OK, but you must protect g2 come Hell or high water.

Yes, you should use vacuum rectification to get a rational B+ rail voltage. Use a "potato masher" 5R4 as the rectifier. The forward drop in a 5R4 is large (a whopping 67 V. @ 250 mA.), while the forward drop in a 5AR4 is small. Pick a horse for the course. The heater draw is 2 A. for both the 5AR4 and the 5R4.

CLC filter the rectifier's O/P. Use a 15 μF. cap. in the 1st position. Several H. are needed in the choke position. Pile the energy storage up in the 2nd cap. position, which is also known as the reservoir position.
Eli D.
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Old 3rd March 2013, 07:49 PM   #3
Ketje is offline Ketje  Belgium
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First put a choke (10H) after the diodes and then a capacitor 50F or more.That gives you the mean voltage of the sinewave,not the peak,it is much lower.However without a load the voltage goes up to the peak,check it with a load.
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