Kofi Annan in: "Tube Amp for Multi-Way Speakers" - Page 13

Kofi Annan · 18th October 2019, 07:51 PM

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

scott17 · 08:07 PM

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...

scott17 · 18th October 2019, 08:36 PM

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.

Kofi Annan · 18th October 2019, 10:07 PM

And we're up and working! Yes!

Thanks to everyone!

PHASE 1: COMPLETE

Kofi Annan · 18th October 2019, 10:11 PM

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

kevinkr · 18th October 2019, 10:36 PM

OMG.. LOL Glad however that you found it...

scott17 · 18th October 2019, 11:22 PM

Glad you've got it working. Yes, that unterminated output could have been bad.

Lingwendil · 19th October 2019, 02:38 PM

Quote:

Originally Posted by Kofi Annan

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

Kofi Annan · 20th October 2019, 03:21 PM

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

scott17 · 20th October 2019, 03:52 PM

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.

18th October 2019, 08:05 PM	#122
scott17 diyAudio Member Join Date: Aug 2009 Location: Long Island, NY	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

18th October 2019, 10:36 PM	#126
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts	OMG.. LOL Glad however that you found it... __________________ "To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine

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18th October 2019, 08:36 PM	#123
scott17 diyAudio Member Join Date: Aug 2009 Location: Long Island, NY	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.

18th October 2019, 10:11 PM	#125
Kofi Annan diyAudio Member Join Date: Jan 2004 Location: US	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

18th October 2019, 11:22 PM	#127
scott17 diyAudio Member Join Date: Aug 2009 Location: Long Island, NY	Glad you've got it working. Yes, that unterminated output could have been bad.

20th October 2019, 03:52 PM	#130
scott17 diyAudio Member Join Date: Aug 2009 Location: Long Island, NY	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.