da-ron
Joined: Jan 02, 2009
Posts: 1307
The original Plymouth, UK.
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Posted on Feb 07 2023 04:06 PM
It's a typical 6G15 unit that I built a few years ago. Last week I used it for rehearsal and it was fine. This week, nothing but a nasty hum. No guitar at all.
So I've checked and checked. I can't identify the problem. The pan, tubes and cables are all OK - I've checked them with a working unit.
When I connect a speaker in place of the pan the guitar sounds OK and the volume responds to the dwell control. I'm confident it's working up to and including the pan. The problem seems to be around the tube used to mix the dry and wet signal. I can't get anything out of this other than a nasty hum.
I've checked all the voltages through the whole unit and they are all within spec. I'm at a loss what could have failed between one practice and the next.
Any help very welcome!
— http://thewaterboarders.bandcamp.com/
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Tqi
Joined: Dec 07, 2014
Posts: 1222
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Posted on Feb 07 2023 05:28 PM
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Last edited: Feb 02, 2024 15:57:37
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da-ron
Joined: Jan 02, 2009
Posts: 1307
The original Plymouth, UK.
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Posted on Feb 08 2023 06:15 PM
Thanks for the help, Tqi. What a nightmare few days trying to solve this one. It turned out to be the 250pF cap between the tone and the mixer.
I'd literally checked everything else, but this capacitor comprised two in parallel as I'd fine tuned it to sound like I wanted it. My assumption was that even if one failed the other would work - the chances of both failing are tiny... aren't they?
Anyway, I've got another capacitor in there now and it's working, which is a great relief. Thanks for taking the time to reply, and thanks for your help.
— http://thewaterboarders.bandcamp.com/
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Tqi
Joined: Dec 07, 2014
Posts: 1222
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Posted on Feb 08 2023 07:11 PM
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Last edited: Feb 02, 2024 15:58:07
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da-ron
Joined: Jan 02, 2009
Posts: 1307
The original Plymouth, UK.
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Posted on Feb 09 2023 02:24 AM
Tqi wrote:
Welcome, though I'm not sure anything I said helped!
Yeah, you did. I would never have bothered checking those final components, they are discrete components and in my experience they are fairly reliable.
— http://thewaterboarders.bandcamp.com/
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da-ron
Joined: Jan 02, 2009
Posts: 1307
The original Plymouth, UK.
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Posted on Feb 09 2023 02:24 AM
Tqi wrote:
Welcome, though I'm not sure anything I said helped!
Yeah, you did. I would never have bothered checking those final components, they are discrete components and in my experience they are fairly reliable.
— http://thewaterboarders.bandcamp.com/
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da-ron
Joined: Jan 02, 2009
Posts: 1307
The original Plymouth, UK.
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Posted on Feb 15 2023 05:47 PM
I thought I'd update this thread. After replacing the 250pF cap off the tone control I did a bit of digging about how two silver mica caps could both fail at the same time.
It seems silver mica caps (which I'd used because tone) are not very reliable, and can be prone to premature failure if heated for too long when soldering. There are also reports that their reliability is significantly less than ceramics.
I've replaced the 250pF cap with a 470pF ceramic cap (the higher value sounds better to my ears) and it's working fine now.
— http://thewaterboarders.bandcamp.com/
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Tqi
Joined: Dec 07, 2014
Posts: 1222
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Posted on Feb 15 2023 07:05 PM
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Last edited: Feb 02, 2024 15:59:49
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