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 Post subject: Crackling?
PostPosted: Sun Jun 07, 2020 5:30 pm 
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Joined: Mon May 18, 2020 4:12 pm
Posts: 7
Ive had my TC-15 for a couple years now and have loved it all, however its making some crackling noises and thought I would take a look. After poking around inside the noise seems to be coming from the EL84 output tubes.

Here are my findings and questions.
Get crackling noise when moving tube gently in socket.
Pin 3 is very microphonic, including wires connected to pin3

Are the microphonics normal? and possibly the socket just need a cleaning?


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 Post subject: Re: Crackling?
PostPosted: Mon Jun 08, 2020 7:27 pm 
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Joined: Tue Mar 25, 2014 3:55 pm
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Location: Central California
Swap the EL84's positions and see if the problem follows the tube to its new socket. if it does you know it's time to replace the tubes.


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 Post subject: Re: Crackling?
PostPosted: Tue Jun 09, 2020 2:17 am 
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Joined: Sat Dec 04, 2010 3:42 pm
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Location: Qualicum Beach, BC
Yes, swap the EL84s as Darren said. But if the problem doesn't follow the tube to the new socket, then it's the socket itself or a bad connection to pin 3.

Sometimes just plugging the tube in and out a few times can clean up a slightly corroded socket. Also have a look at the pins on the tube and make sure they are clean.


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 Post subject: Re: Crackling?
PostPosted: Fri Jun 12, 2020 10:54 am 
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Thanks, unfortunately both tubes and sockets are doing the same thing so I will try a set of new tubes in it.
However are the microphonics normal? It seems quite excessive, since I can lightly tap on even the lead where pin 3 connects to the turret board and hear the thumping thru the speaker.


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 Post subject: Re: Crackling?
PostPosted: Sun Jun 14, 2020 4:16 pm 
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I was going to check my TC-15 to see how microphonic, if any, the wire for the output tube cathodes is. But then I remembered I stole the EL84s from it a while ago to fix a Vox AC-30 and still haven't replaced them.

I don't think it's normal to have microphonics on the output tubes, though. Check for bad connections at each end of the wire that runs from pin 3 on the tube sockets to the board. Also check the connections to the 150-ohm resistor and 220uF capacitor on the board and their grounds.


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 Post subject: Re: Crackling?
PostPosted: Tue Jun 16, 2020 3:00 pm 
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Joined: Mon May 18, 2020 4:12 pm
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Well seem to have found the issue. A new set of EL84 tubes and no more microphonics and no crackling in the socket. Interesting how both tubes failed in the same way at the same time.
Thanks all for your input:)


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 Post subject: Re: Crackling?
PostPosted: Tue Jun 16, 2020 4:15 pm 
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Joined: Sat Dec 04, 2010 3:42 pm
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Location: Qualicum Beach, BC
When amps that have been working for a couple of years develop problems, it's usually due to either tubes that have gone bad or connections that have worked loose. Unusual for both EL84s to go bad at the same time with the same problem. That usually indicates a problem with something common to both of them.

Anyway, the easiest thing to do is change the tubes. Glad that fixed the problem.


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