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Post subject: Twin amp gain Squeal
Posted: Tue Jul 13, 2010 7:08 am
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Hey Everyone,
I just picked up a mid 90s Twin amp and i really like it. The only problem I've had is when i turn the gain on the second channel above 6 i get a high pitch squeal. I've fooled around with all the settings on the amp and my guitar as much as i can but i can't seem to get it to go away. Anyone know any possible solutions?
Thanks.


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Posted: Tue Jul 13, 2010 3:08 pm
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Do you use high and low inputs?

Did you change V3?

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Posted: Tue Jul 13, 2010 4:43 pm
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It squeals whether i have the guitar plugged in or not. When i got it, the amp was missing a preamp tube which i replaced with a Groove Tubes 12AX7.


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Posted: Wed Jul 14, 2010 9:06 am
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To make sure: it's a 94 twin amp, please confirm.

Groove Tube 12AX7 is correct (often russian valves) excepted for V5 that uses 12AT7 (lower gain) for the reverb (and be prudent with V8 -dephaser for the push pull- it better to use a 12AX7 matched one).

A simple test can indicate if the issue is located in the preamp or the amp.

- Put a jack in "Power IN" connected to your guitar at volum 0:
- Squeal Y/N

Let me know.

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Posted: Sun Jul 18, 2010 12:43 pm
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The amp was made in June of 96. I did the test and yes there was still a squeal.


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Posted: Sun Jul 18, 2010 2:32 pm
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OK,

The issue seems to come from the power amp or the supply.

(All maintenance shall be done at amp OFF and unplugged)

Still with the guitar connected directly in "POWER IN" jack, the test is:

to swap V7 with another 12AX7;
--> Squeal Y/N
Put back the valve if Y

to swap V8 with another 12AX7; Take care often V8 has the double triode with a good matching. Put a mark on it to not loose it.
--> Squeal Y/N
Put back the valve with the mark if Y

let me know

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