Greetings, I have a 86 JCM 2203 that I have only replaced preamp tubes in the time I’ve owned it and have had no issues playing through a matching year JCM 4x12. Recently I got some new JJ’s and today when I changed the v1 I got no sound at all out of the low input and an extremely low volume on the high input even when on 7-8. I changed back to the v1 I had before( a groove tube) and no issue, works as it always has. I then changed it to three or four known good tubes and had the same volume/ no sound issue. The Groove Tube seems to be the only one working. This is a new issue I’ve never had before. The only thing I’ve done different recently is try the amp through my new captor x ( attenuated and into my interface/ logic x) where I found the sound fizzy and frankly disappointing as I was hoping for Marshall glory at a reasonable volume. I have a PT-20 , Peavey Classic 20 and an old Epiphone as well and have had no issues with the captor or otherwise. I tried the cables/ cabinet / captor with my other heads as well as the different tubes and all work fine. Any help or suggestions would be greatly appreciated.
Only one tube in 2203 working
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paul-e-mann
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The new JJ's are bad dont you think if everything was working before??
ToneWitch
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Sounds like you have a bad preamp tube.
I agree on the attenuator. I got the captor mainly for recording/ cab sims . I have new JJ’s in my PT and they work fine. If I pull v1 and go into the JCM I get the issue. I go back into the PT and it works fine. So I’m at a loss. I will try cleaning like you suggested . It would be great if it was as simple as some some deoxit
That’s where my confusion is. I will take a JJ from my PT and stick in v1 of the JCM and get nothing, put it back in the PT and it works no issue. I have swapped tubes/ positions with good tubes. It’s literally one Groove Tube that works
StingRay85
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Try to be a bit more clear on what you exactly tested. If you put a bad tube in V2 or V3, it doesn't matter what happens with V1 you will never get sound. But it doesn't mean there's something wrong with V1. So to test a tube if it works or not, you better make sure V2 and V3 work 
Matthews Guitars
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Getting a new bad preamp tube is possible. Getting several new bad preamp tubes is SUPER unlikely.
Don't get confused. Replace ONE tube at a time in a situation like this.
I pre-test all my tubes before they go into an amp, using my tube tester. If you don't have a tube tester, test all like tubes in a single socket in a good amp to verify they work before you distribute them to their new amplifier homes. I'd test every new 12AX7 in V1 of one of my amps, and test 12AT7s in the AT7 sockets of my Fender amp to test those.
It's all but impossible for an amp to work well on a good old used tube but not work at all on a good new tube of the same type.
Don't get confused. Replace ONE tube at a time in a situation like this.
I pre-test all my tubes before they go into an amp, using my tube tester. If you don't have a tube tester, test all like tubes in a single socket in a good amp to verify they work before you distribute them to their new amplifier homes. I'd test every new 12AX7 in V1 of one of my amps, and test 12AT7s in the AT7 sockets of my Fender amp to test those.
It's all but impossible for an amp to work well on a good old used tube but not work at all on a good new tube of the same type.
Tatzmann
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I had very similar things happen
couple of times, where a preamp
caused noises or appeared weak
in only 1 amp and socket, but worked
fine in other sockets or amps.
Did not really solve it because another
tube fixed it.
Most straightforward guess would be
the socket.
couple of times, where a preamp
caused noises or appeared weak
in only 1 amp and socket, but worked
fine in other sockets or amps.
Did not really solve it because another
tube fixed it.
Most straightforward guess would be
the socket.
Try to be a bit more clear on what you exactly tested. If you put a bad tube in V2 or V3, it doesn't matter what happens with V1 you will never get sound. But it doesn't mean there's something wrong with V1. So to test a tube if it works or not, you better make sure V2 and V3 work
So this is how I have been testing. I have only tested using my amps as a reference. If they work in my PT or my Peavey , which they have, I am assuming they work. I have a DMM and experience with electronics but not yet the knowledge and confidence to work in and around the high voltages. Today I took the three JJ’s out of my PT-20 and put them in my Marshall. I had played the PT an hour before so I know they are good tubes and I get nothing but a extremely low volume on the high input and that’s on like 8. I can’t even be in the room if the amps on 2 it’s such a monster. I swap the order around in the Marshall and get the same result. I put the JJ’s back in the Friedman and I have no issue at all, sounds mint. I have 6-8 JJs , 3 ARS tubes , a handful of no name tubes and a lone Groove Tube. The GT is the only tube that works and it has to be in v1 to do so. I currently have the GT in v1 and the ARS in v2,v3 and the amp works and actually sounds nice . I take the GT and swap it with the ARS in v2 and get the same issue, swap the GT back into v1 and I’m back in business. This is a new issue as I’ve had three JJs in there in the past with no issue.
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Yep. My guess as well, Socket. I would retension the socket. Perhaps the pins are slightly different sizes, and the offending amps socket is slightly loose.
matttornado
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sounds like the groove tube is the only one making good contact . the others known good tubes are not.
maybe the groove tube has fatter pins?
maybe the groove tube has fatter pins?
El Gringo
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I get the concept of attenuators for when you need lower volume . It just seems to me that tubes get cooked way to fast when running hot like that . I know it has it's place in folks tone arsenals , but at a cost . Maybe I am looking at this the wrong way ?
thetragichero
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so i drive my wife's corolla when i just need to tool around town instead of my big pickup truck because the extra power/towing ability is a waste. when i want to play at lower volume i use a smaller combo. there's something to be said about using the right tool for the right job
Guitar Amp Tools
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I always unplug the amp, leave the power switch and stby in the "on" position and let the amp sit for 5 minutes. Then discharge the power supply through a resistor and check for voltages from each pins of the power tube socket to the chassis. If everything looks good I jam a screwdriver across the + and - terminals of each of the big capacitors just to make sure that if I made a mistake a screwdriver gets shocked and not me. If I'm in a hurry I'll just start jamming a screwdriver across the terminals of the caps, the high voltage pop is fun. You have to wait a minute and do it again because the caps will re-charge somewhat
