2203 No Preamp control working

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acdc-angus
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2203 No Preamp control working

Post by acdc-angus » Sat Feb 24, 2024 12:58 pm

Hi,

I maintenance a JMP 2203 from the 70's for a friend and I have a weird issue that I can't point on.

What I changed :
- 6 Filters Caps
- 2x 10uf Bias
- Add 4 1ohm resistors on power socket
- Relocate the 4ohm NFB to 8ohm
- Relocate the 68k and the Preamp middle pin directly to the V1 socket
- Replace all the pots
- Remove the 100pf added on the V1 probably because of the NFB on 4ohms.

Everything works good, all current seems good too.

The weird issue is : It sound perfectly, but the Master act like the Volume I of a SLP and the preamp pot doesn't work at all.
I tried 3 pots, another set of tubes, checks the schematic and the replica I made. I can't point the issue. So if you have an idea, please :peace:

acdc-angus
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Posts: 6
Joined: Fri Oct 24, 2014 8:03 pm
Just the numbers in order: 13492

Re: 2203 No Preamp control working

Post by acdc-angus » Sun Feb 25, 2024 6:08 am

The forum is dead? Or there are still someone to help sometime?

Tazin
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Joined: Fri Jan 19, 2007 8:54 pm

Re: 2203 No Preamp control working

Post by Tazin » Mon Feb 26, 2024 9:41 am

Since you replaced all the potentiometers, is there a chance you wired something incorrectly?

acdc-angus
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Posts: 6
Joined: Fri Oct 24, 2014 8:03 pm
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Re: 2203 No Preamp control working

Post by acdc-angus » Mon Mar 04, 2024 9:30 am

Tazin wrote:
Mon Feb 26, 2024 9:41 am
Since you replaced all the potentiometers, is there a chance you wired something incorrectly?
I finally find out I just swapped the two blue wires on the V1

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