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Topic: Little Walter Head |
Danny Caporn
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Posted 21 Jul 2019 3:47 am |
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Have a Little Walter 25/50 head that has the octal preamp tubes into 6L6 outputs.
This has been unstable since new and even with new tubes is oscillating at high frequency any time you touch the tone or volume.
Tried various means to contact Phil unsuccessfully.
I am an experienced Tech but not familiar with this design.
The customer and I reside in Perth, Western Australia.
The amp and speaker cab were quite a significant investment so with all the positive hype re these amps we would like some help to resolve this issue so we came enjoy this amp working.
Kind Regards
Danny |
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Norman Evans
From:
Tennessee
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 21 Jul 2019 6:31 am
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I repositioned some of the lead wires in my 50-watt to avoid parasitic oscillation. Just moved them around until things quieted down and made note of where they needed to be. Most of my issues were in the preamp section.
The leads on mine are springy and thus didn't stay in place when moved - the old push-back cloth wire would stay in place. So I used RTV silicone to hold them in place once they were positioned correctly. There are undoubtedly many varieties of "goop" that would work for this purpose. Many amp makers do this to keep leads in place.
Another point: the octal preamp tubes in my amp when I got it were very microphonic. My amp was not new, so I don't know if this was true when it was. I finally found some NOS 6SC7 and 6SL7 examples that weren't, and that also helped a lot. A lot of what's out there are very microphonic, at least the ones I've tried. |
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Danny Caporn
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Posted 31 Jul 2019 2:35 am
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| Problem solved, please close |
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Steven Paris
From:
Los Angeles
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Posted 1 Aug 2019 2:33 am
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What was the solution?
_________________
Emmons & Peavey |
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Danny Caporn
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Posted 3 Aug 2019 9:18 pm
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After many years of fixing guitar amps you often miss the obvious.
This amplifier has two inputs each is directly connected to grids 1 and 2 of the twin triode preamp tube.
The input jacks are mono with a contact to ground.
Input 1 is normally used.
When input 2 was used the fault did not occur.
The contact of input 2 was found to be high resistant resulting in the preamp tube amplifying parasitic frequencies when using the input 1.
Even the best jacks need to be plugged in periodically to clean the contact.
New input jack installed, all good. |
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