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Old 8th March 2013, 05:27 PM   #221
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Been in Asia for a couple of weeks and a bit out of touch...

I finally remembered to list the power supply PCB on eBay, if you were looking for one:

DIY PCB Power Supply Board for Tube Amps | eBay

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Old 15th April 2013, 08:12 PM   #222
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I'm planning on building a pair of monoblocks based on this PCB, and the power supply PCB for a friend. I'm aiming for 30W-40W using Edcor 60W OPT's and a pair of EL34. Using the 4.2K Edcor and the 40% screen taps, to reach my target of ~35W at <1% THD I believe I'll need a B+ of 400V.

Antek has a 2x150V transformer (AS-1T150) which with Pmillett's power supply design will give me a B+ of around 400-420Vdc. I'd also need to use an AN-0240 to supply the 80Vac for the bias circuit. I like this idea, as it would be under 50$ per monoblock. The problem is that Antek is out of commission currently. They're piecing the operation back together, but it looks like it could be months before they get to the high voltage units. We'll see when the next shipment is posted this month.

The other options are using an Edcor XPWR220-120 (295V@350mA, 6.3V@8A) and another transformer for the 80Vac bias supply, having Edcor do a custom job, or using the Classictone transformer Pete used and dropping the B+ some with a bigger choke or resistors...

Any other ideas?
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Old 20th November 2013, 08:06 PM   #223
wicked1 is offline wicked1  United States
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I finally got one monoblock completed and in its chassis. I've tested everything, and have found one problem.
I measure across the 10k resistors on the 12hl7 anodes to set the balance, and only measure about 4v on each resistor. In the other channel that's still just tacked together on my workbench, I measure about 9v across those resistors.
Everything else checks out fine.. the voltage at every pin of the hl7's match in both channels.

The tubes should be burning about 8ma. If I didn't have a 2nd amp to compare with, I'd assume (maybe incorrectly) that the extra power I'm not measuring across the 10k resistor is being taken across the feedback resistor. But, both channels should be the same..

I measured the V drop across r17 (set resistor for the 10m45), and get 37ma as I should, so the CCS is correct.

Here's the schematic
http://www.pmillett.com/file_downloads/ppdrv2.pdf

Any ideas?
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Old 20th November 2013, 11:23 PM   #224
tomlang is offline tomlang  United States
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That. Is. Awesome. What output tubes are those. Mr. Wicked??
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Old 20th November 2013, 11:52 PM   #225
AJT is offline AJT  Philippines
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829B

one problem with this tubes is matching between sections,
i have seen tubes that had one side red plate.
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Old 20th November 2013, 11:57 PM   #226
AJT is offline AJT  Philippines
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Quote:
Originally Posted by wicked1 View Post
I finally got one monoblock completed and in its chassis. I've tested everything, and have found one problem.
I measure across the 10k resistors on the 12hl7 anodes to set the balance, and only measure about 4v on each resistor. In the other channel that's still just tacked together on my workbench, I measure about 9v across those resistors.
Everything else checks out fine.. the voltage at every pin of the hl7's match in both channels.

The tubes should be burning about 8ma. If I didn't have a 2nd amp to compare with, I'd assume (maybe incorrectly) that the extra power I'm not measuring across the 10k resistor is being taken across the feedback resistor. But, both channels should be the same..

I measured the V drop across r17 (set resistor for the 10m45), and get 37ma as I should, so the CCS is correct.

Here's the schematic
http://www.pmillett.com/file_downloads/ppdrv2.pdf

Any ideas?
did you adjust the driver balance pot? that pot is for compensating for unequal transconductance of the 12hl7's...
at setup, this pot is set at midpoint, then adjusted towards to the tube that has lower current...

if you have several 12hl7's you can test them for gm matching...
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Old 21st November 2013, 12:40 AM   #227
wicked1 is offline wicked1  United States
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Tomlang, thanks! And like AJT says, 829b's. I regulated the screens and bias. Otherwise, it's mostly the same as Pete's schematic.
I had a bunch to choose from so these are matched fairly well. Few ma difference between sections at worst. I might be adding a bias adjustment for each section. I've got the parts but am not sure I want to add more caps (or unnecessary complexity). So.. I'll frequently test each section for a while and decide later..

AJT
Yes, that's in balance, each at 4v drop. Other monoblock is about 9v drop across each 10k resistor.
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Old 21st November 2013, 02:53 AM   #228
wicked1 is offline wicked1  United States
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I disconnected the ul taps local feedback (e-linear?), and it all biased up normally.
And I realized my comparison w/ my workbench copy was flawed.. 9v across 10000 ohms is only .9ma. So, there's more going on w/ the feedback than I understand right now, but both amps are functioning the same, w/in tolerances.
I think everything is ok.
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Old 21st November 2013, 04:08 AM   #229
AJT is offline AJT  Philippines
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Quote:
Originally Posted by wicked1 View Post
I disconnected the ul taps local feedback (e-linear?), and it all biased up normally.
And I realized my comparison w/ my workbench copy was flawed.. 9v across 10000 ohms is only .9ma. So, there's more going on w/ the feedback than I understand right now, but both amps are functioning the same, w/in tolerances.
I think everything is ok.
you can series connect a 1k resistor on your CCS and then you can verify that your CCS is feeding the correct current...
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Old 21st July 2014, 02:59 PM   #230
wicked1 is offline wicked1  United States
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Pete (Or anyone),
Why such a low value Rg (r31 and r3) on the output tubes?

Schematic:
http://www.pmillett.com/file_downloads/ppdrv2.pdf
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