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Kofi Annan in: "Tube Amp for Multi-Way Speakers"
Kofi Annan in: "Tube Amp for Multi-Way Speakers"
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Old 18th October 2019, 07:51 PM   #121
Kofi Annan is offline Kofi Annan  United States
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Found it!

I started wiggling stuff and found that when I wiggled the plate connection to the OPT the resistance started to jump around. Turns out a Stupid Solder Blob That Made Problems was the culprit.

Finally got all the solder wicked away and am beginning to hook everything back up for testing.

FAULT #1 ELIMINATED.

KOFI
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Old 18th October 2019, 08:05 PM   #122
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Ah ha! Good catch.
I haven't thought it through too carefully, but that may be the reason for the differing readings-to-ground for your screen taps. You were reading through varying lengths of windings. With just one plate connection "shorted" to ground, the problem would show up on both OTs since the B+ connection is common to both.

I'm sure you'll look carefully, and take the readings again, but where there is one solder blob there may be...

Last edited by scott17; 18th October 2019 at 08:07 PM. Reason: additional
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Old 18th October 2019, 08:36 PM   #123
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The 80R dropping resistor in your power supply will be dissipating ~10W, so you probably want to use at least a 30W chassis mount or maybe (3) 250R-10W in parallel.
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Old 18th October 2019, 10:07 PM   #124
Kofi Annan is offline Kofi Annan  United States
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And we're up and working! Yes!

Thanks to everyone!

PHASE 1: COMPLETE
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Old 18th October 2019, 10:11 PM   #125
Kofi Annan is offline Kofi Annan  United States
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Funny Kofi Story:

So, I wasn't getting any output from one of the channels initially. Looked like signal was going in but not getting out. Couple hours roll by and I can't for the life of me...

Then I went to swap the outputs to see and I noticed that I DID NOT STRIP THE PLASTIC OFF THE SPEAKER CABLES.

Yikes, Kofi. That was a bad one.

Kofi
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Old 18th October 2019, 10:36 PM   #126
kevinkr is offline kevinkr  United States
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Kofi Annan in: "Tube Amp for Multi-Way Speakers"
OMG.. LOL Glad however that you found it...
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Old 18th October 2019, 11:22 PM   #127
scott17 is offline scott17
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Glad you've got it working. Yes, that unterminated output could have been bad.
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Old 19th October 2019, 02:38 PM   #128
Lingwendil is offline Lingwendil  United States
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Quote:
Originally Posted by Kofi Annan View Post
Funny Kofi Story:

So, I wasn't getting any output from one of the channels initially. Looked like signal was going in but not getting out. Couple hours roll by and I can't for the life of me...

Then I went to swap the outputs to see and I noticed that I DID NOT STRIP THE PLASTIC OFF THE SPEAKER CABLES.

Yikes, Kofi. That was a bad one.

Kofi
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Old 20th October 2019, 03:21 PM   #129
Kofi Annan is offline Kofi Annan  United States
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OK-- question for the council:

So, I need to drop about 30 - 50 volts to hit a supply voltage of around 300VDC to 320VDC and I'm running into some space restrictions in the chassis.

I'm sure I could drop the B+ by lowering the first cap to around 10uF or so (guessing at the value for the moment), but would removing the final filter cap be an option (see schematics attached)?

Thoughts?

Kofi
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File Type: png no final cap PSU.png (207.3 KB, 78 views)
File Type: png EL84PPP FINAL wirh Mod PSU.png (402.9 KB, 71 views)
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Old 20th October 2019, 03:52 PM   #130
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I'd leave the final cap in place. You could reduce the first capacitor to ~100uF to minimize the initial turn-on surge, and use something like 25R-10W in each leg of the PT secondary before the rectifier.
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