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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 18th July 2018, 12:25 PM   #31
trobbins is offline trobbins  Australia
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The OA2's in post #1 schematic only regulate the 6N7 grid voltage. The current through the OA2's depends on the voltage at the anode of the 6N7 and the 16K dropper resistor.

It sounds like you are referring to using OA2's to regulate the screen voltage directly (ie. not 6N7 regulator type circuitry).
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Old 18th July 2018, 12:34 PM   #32
sony6060 is offline sony6060  United States
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Yes, I like more simple circuits.
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Old 18th July 2018, 01:27 PM   #33
trobbins is offline trobbins  Australia
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In your setup, if you had one string of OA2's to provide a common screen voltage for a PP pair of 807, you would set up the OA2 string to conduct a bit under 30mA at idle. At turn-on, once the OA2's strike, the OA2 string would conduct about 40mA until the 807's start conducting (maybe a bit more if B+ was initially high). The average screen current can then increase from idle level by about 20-25mA before regulation is lost.
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Old 18th July 2018, 01:37 PM   #34
jhstewart9 is offline jhstewart9  Canada
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An 807 could be used as a series pass tube & has a plate cap. Better than a 6N7.
And also matches the amp chassis.
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Old 18th July 2018, 02:15 PM   #35
H713 is offline H713  United States
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To clear any concerns about the 6N7, that tube is being replaced with a triode-strapped 6L6GC (Or just another 1625... we'll see) in my latest iteration of the schematic.
Other minor change is that the 6J5 and 12BH7 are being replaced by a single 12SN7, and the power tubes are now 1625s instead of 807s. I'll therefore just run a 12V heater all around. Tubes are cheaper, and I'll be pulling less current through the heater wires that will be in the same multi-conductor cable as the B+ and bias voltage. I probably won't be able to use a very heavy gauge for those heater wires, so keeping the current under 3 Amps is a good thing. And not to worry, the Tek transformer has about a million heater windings.
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File Type: png 807 PSU Latest.PNG (41.6 KB, 40 views)
File Type: png 1625 Amp Latest.PNG (25.9 KB, 41 views)
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Old 18th July 2018, 02:41 PM   #36
jhstewart9 is offline jhstewart9  Canada
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6L6GC H-K max is 200V either way.(+ve or -ve) So should have a dedicated heater transformer. Guess it will anyway if the rest ate on 12V.

The amp as shewn is not connected for ordinary NFB. Input will look like 10K divided by the amp gain.
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Old 18th July 2018, 03:24 PM   #37
H713 is offline H713  United States
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Yep- I'll throw it on it's own winding then float the heaters. Not to worry.

Also, it looks like I edited and posted a very old version of my schematic. This is how the feedback was supposed to be connected.
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File Type: png 807 Feedback Rerevised.PNG (27.3 KB, 36 views)
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