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1960 Bassman circuit question

MapleFlame

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Jul 3, 2005
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14,029
Amp works in instrument channel but not microphone that just muff. I only have use of Presence and instrument Volume pots. Treble, Bass and Mid does not work. No scratchyness when turning. I double checked the wiring, seems fine. I replaced the power and output trannie. Any suggestions?
 

thejaf

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Oct 27, 2006
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If the tone controls don't work but signal passes, I'd suggest ground connection (tail of the mid range pot - also check mid pot, as it's the last connection to ground also).
 

MapleFlame

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Jul 3, 2005
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If the tone controls don't work but signal passes, I'd suggest ground connection (tail of the mid range pot - also check mid pot, as it's the last connection to ground also).

It's a brand new 25k pot, the previous pot was a cheap Japanese that hardly changed the dynamics of midrange. I will try looking to see if it has good grounding. Thank you
 

MapleFlame

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Jul 3, 2005
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Yes my ground solder joint on left lug was not good enough. Even though it's a new pot, I think its a bad one, as I turn it, it pops and at certain points the other tone controls work. It sucks because when it's off, the amp cranks. I'm going to put in the old pot to see if that's it.
 

MapleFlame

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Good news, put the old pot in and wallahh it works. I will start a thread on all the stages I took pictures of. Thank you "Thejaf"
 

MapleFlame

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Good news, glad to help. :salude

Another question for you, my microphone channel is not working. I took the pot apart and cleaned it. What is weird, when plugged into #1 instrument channel, the microphone volume interacts when turned up to 4-5 then makes noises. While plugged into mic channel gets nothing and when turning up pops and flubbing noise. I touched up cap solder joint and looked at everything I could think ok. Input jacks? Maybe
 

thejaf

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Oct 27, 2006
Messages
517
Another question for you, my microphone channel is not working. I took the pot apart and cleaned it. What is weird, when plugged into #1 instrument channel, the microphone volume interacts when turned up to 4-5 then makes noises. While plugged into mic channel gets nothing and when turning up pops and flubbing noise. I touched up cap solder joint and looked at everything I could think ok. Input jacks? Maybe

The interaction makes sense, as looking at schematic the two volume pots are in parallel with respect to ground.

Mic channel not working could be input jack, and again check the grounds. You could carefully run a alligator clip wire from known good jack over to output of mic jack, check for signal to isolate the jack itself. Would be ghetto, but just for testing. :##
 

MapleFlame

Well-known member
Joined
Jul 3, 2005
Messages
14,029
The interaction makes sense, as looking at schematic the two volume pots are in parallel with respect to ground.

Mic channel not working could be input jack, and again check the grounds. You could carefully run a alligator clip wire from known good jack over to output of mic jack, check for signal to isolate the jack itself. Would be ghetto, but just for testing. :##

Crazy to think, I go through all that work and didn't do the obvious, try swapping tubes, embarrassing. I swap tubes on every amp to get the tone I like. Guess I was thinking the worst that it had to be something circuit related.
Thank you again.
 
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