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An Excessively Complicated External Power Supply and Bias Circuit for 807 Amp
An Excessively Complicated External Power Supply and Bias Circuit for 807 Amp
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Old 17th July 2018, 05:52 PM   #21
sony6060 is offline sony6060  United States
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My bottom line on P design for this 807 amp.

Screen supply- I would use 6 0A2- less complicated, highly reliable & inexpensive. Bias- Standard non electronic regulated bias. Simpler design just using capacitors and resistors- less complicated, highly reliable, no noise issues due to extremely low current draw. High voltage- use just enough capacitance with the resistor to rid the top 10 volts of noise & trash for about 2 volts AC ripple output. Nothing more needed for push-pull design. It is a CRC network.
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Old 17th July 2018, 06:26 PM   #22
H713 is offline H713  United States
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So you're saying I should use 6 0A2 (or 0D3) instead of using a pair plus a PAS tube? I already have a bunch of stray 6L6s (not part of a pair), so it's no extra cost. What's the advantage of using that many 0A2s instead?

Also, I already have the 2900 @250V capacitors (soda-can sized Sprague Powerlytics) that I pulled from something, so I was planning to use them up on this project.
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Old 17th July 2018, 06:30 PM   #23
sony6060 is offline sony6060  United States
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I am not asking you to build to my design. My design is what I would build.
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Old 18th July 2018, 09:29 AM   #24
jhstewart9 is offline jhstewart9  Canada
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The GE 6N7 data sheet shows 90V max for H-K.

For the 807 G2 current requirements & the driver the 6N7 will be running +ve control grid. Not the greatest choice for a series regulator. In this cct the Pd max may be exceeded. But it wud work, for a while.

Something like 50 nF across the 0A2s will remove much of the noise. If the cap selected is too large you may have an oscillator!

Not sure where 6X 0A2 would fit in as an alternative. Trying to do series/paralleled? That won't fly, one pair will start & hold the others off. But two 0D3s might be OK.

Am I missing something?
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Old 18th July 2018, 10:36 AM   #25
sony6060 is offline sony6060  United States
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Oa2 would have overcurrent at start up due to 807s not drawing screen current. Voltage would be high enough to fire off all regulator tubes. I would use same brand and try to find the older 0a2 with radioactive element inside.
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Old 18th July 2018, 11:05 AM   #26
trobbins is offline trobbins  Australia
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Quote:
Originally Posted by sony6060 View Post
Oa2 would have overcurrent at start up due to 807s not drawing screen current.
Are you assuming that the voltage after the choke would sag significantly from normal 807 screen, and otherwise be so high that the voltage drop across the 16k would cause OA2 current to exceed max rating?
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Old 18th July 2018, 11:23 AM   #27
sony6060 is offline sony6060  United States
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Quote:
Originally Posted by trobbins View Post
Are you assuming that the voltage after the choke would sag significantly from normal 807 screen, and otherwise be so high that the voltage drop across the 16k would cause OA2 current to exceed max rating?
I way I would set it up is 35ma per tube would be exceeded until the 807s draw screen current. That would not overheat and damage the regulator tubes during that short duration. But at the same time guarantee all regulator tubes light. I have seen it designed that way for ham radio equipment.

Last edited by sony6060; 18th July 2018 at 11:26 AM.
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Old 18th July 2018, 11:44 AM   #28
trobbins is offline trobbins  Australia
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Are you referring to H713's schematic in post #1 ?
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Old 18th July 2018, 12:04 PM   #29
sony6060 is offline sony6060  United States
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6L6GC in class AB1 with 450 volts plate and about 300 volts screen draw 6ma each at idle and 22ma at full signal. Use a variable resistor and set 0a2s for about 100ma current draw at 807 screen idle current. At 22 ma screen current per 807 tube, 17 ma of reserve is available from the 0A2s. The 807 may vary from 6L6GC somewhat, but tube internals should be the same as 6L6GC.
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Old 18th July 2018, 12:24 PM   #30
lcsaszar is offline lcsaszar  Hungary
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Quote:
Originally Posted by H713 View Post
Yeah, as I got to thinking about it there's no reason for balance pot between the two channels.

Historically I've just copied the bias supply from an amp using similar tubes, although I admit that I've never thought much of it beyond being an adjustable negative voltage supply.

This is the bias supply from the amp I'm currently working on, which seems a little more typical.
Move the 10uF capacitors out of signal path.
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