The Amp Garage

To all that provided feedback, thank you!. Amp is up and running and sounding great. Should last another 36 years.

Is there any hum or buzz coming out of the speaker? Before the changes, I literally heard nothing from the amp or speakers until I realized that V2 was not getting warm and noticed that the tube was really loose in the socket. Once I tightened it up a some, I could hear a signal but not from the sp...

I replaced the output transformer, preamp tube sockets, filter caps, and bias caps. I used a current limiter on start up and discovered a short that turned out to be a shorted diode in the rectifier, so I replaced all the diodes in the rectifier and bias circuit. Voltages look much better but still ...

It’s pretty easy with just your eyes and ears to tell of you have a OT that’s shorted. Get the room dark and play the amp cranked while you look at the output tubes. If the preamp section is working well you will see the output tubes flash up brite on the inside. If you do see that then the output ...

With all 3 valves showing signs of life, I plugged in a guitar and got sound. I could hear the guitar very faintly with some crackle and pop from time to time. All controls were dimed. All 3 of the preamp tubes seem very loose but V2 for some reason doesn't maintain a connection. However, when it do...

Measuring the speaker output jacks using the speaker cable tip/sleeve I read 0 ohms. That's about what you should read. The voltages you listed for V2 are messed up and would account for no sound. V3 pin 1 is wrong also. It should read about the same as pin 6. Recheck the voltages for V2 and V3. Th...

I think I may have found an issue with the V2 socket. I had fired the amp up and saw glow in V1 and V3 but nothing in V2. I left the room for a minute and when I came back V2 was glowing brighter than the other two. I put the tube shields on and checked the voltage at pin 3 and still got no reading....

So there's definitely a glowing heater at the top of the V3 pins1-3 triode (ie as well as the one at the top of the pins 6-8 triode)? Whatever, a non functional V3 pins1-3 triode might not completely mute the amp, so your task is to identify the bad connection which is preventing the valve in V2 fr...

The wire that wraps at the output jacks used to ground the FIXED DI. That dual pot is added where a cap, resistor, and jack used to be. Where do the wires go? Looks like some attempt at a master volume.It appears to still be installed. It looks like it has the output tube grid feeds attached but it...

Thanks for the quick responses!

V2 doesn't seem to be but V3 is getting hot. The voltages look off (especially for V2). If it were working correctly it would be conducting and you should have a volt or two on pin 3. See this page for a very general voltage chart: https://mhuss.com/MyJCM/vchart.html Note that this is for an 82 amp...

V2 doesn't seem to be but V3 is getting hot. The voltages look off (especially for V2). If it were working correctly it would be conducting and you should have a volt or two on pin 3. See this page for a very general voltage chart: https://mhuss.com/MyJCM/vchart.html Note that this is for an 82 amp...

Helmholtz wrote: ↑Tue Nov 26, 2024 11:52 pm Three tubes in V3?

Copy/Paste...forgot to change the power tubes. It's corrected now, thanks!

pdf64 wrote: ↑Tue Nov 26, 2024 2:08 pm So this is a 2204? JCM800 is a product range, dozens of models.
What year?
Are the valves in V2&3 actually getting warm?

Based on the SN it was built in 1988. V2 doesn't seem to be but V3 is getting hot.

I'm new to the forum but have been here looking for a solution for a few days. I found a post from 15 years ago with the same title but it doesn't seem they posted/confirmed the solution. I have some experience building a 50W Plexi kit and have made some repairs to my 65 Deluxe Reissue, so a buddy a...