Tube Amp Archive

I checked every connection and reflowed everything but it did not help. So I tried taking a chopstick and poking all the connections and moving the wires around until I discovered the culprit. My V2 pin 8 connection was intermittently bad somewhere between the pin and turret. I could make it work or...

With all the tubes in and the amp on hook up a voltmeter set to read AC across the speaker output, if you read anything over 1 volt then the amp is oscillating due to your build/ layout or you may need to swap the plate wires ( blue and green) feeding the OT. I didn't hear any oscillation last i ha...

When you put the power tubes in, what load was on the amp, eg speaker cab, big beefy load resistor? Point being that an unloaded amp can go nuts. What were the control settings? It’s best to zero them all at this stage. Verify that the shorting contacts of the input jack sockets are properly connec...

After a few minutes the power tubes get very hot. the preamp tubes are still cool to the touch. The voltages in the preamp spike to this: V1 pin 1 - 440 V1 pin 2 - signal V1 pin 3 - 0 V1 pin 4 - 3.3 V1 pin 5 - 3.3 V1 pin 6 - 440 V1 pin 7 - signal V1 pin 8 - 0 V1 pin 9 - 3.3 V2 pin 1 - 440 V2 pin 2 -...

Readings with power tubes, immediately after powerup, all knobs at zero V1 pin 1 - 281 V1 pin 2 - signal V1 pin 3 - 2.34 V1 pin 4 - 3.3 V1 pin 5 - 3.3 V1 pin 6 - 331 V1 pin 7 - signal V1 pin 8 - 3.3 V1 pin 9 -3.3 V2 pin 1 - 204 V2 pin 2 - signal V2 pin 3 - 1.43 V2 pin 4 - 3.3 V2 pin 5 - 3.3 V2 pin 6...

Some more detailed voltage info: I'm getting 122v from the wall I'm getting 360vac from the hv leads off the power transformer i get 494 vdc after the rectifier diodes bias voltage is -49 All my heaters seem to be functioning, i'm getting about 3.3vac on all 5 tubes I'm using a 1x12 cabinet with a 2...

Here are a bunch of pictures and the schematic/layout

Hi Folks, I built a 50w JCM800. Having issues finishing it, it is CRAZY dynamic. The V1-V3 plate voltages are more reasonable if i have the preamp tubes in and the power tubes NOT in. With just preamp tubes: V1 pin1 - 295 V1 pin6 - 353 V2 pin1 - 216 V2 pin6 - 408 V3 pin1 - 286 V3 pin6 - 265 However,...

Yes it's working now! I will post clips after I get back from a summer trip. Sounds good, a bit trebly, and it's ball-crushingly loud, both of which I expected. I am going to do a series of mods to it now, which was always the plan. Thanks for the complement! I've done some little projects before, a...

Thanks!

Yes it's the Mojotone "British 800 50w" kit.

Ok so i think I found a sketch joint on the v3 cathode so i reflowed it and voltages look better! You rule Xtian!

Ok here are a bunch of shots, thanks for the help. Yes, first amp i'm afraid so potential for dumb mistakes is high. Let me know if there's anything you'd like better shots of or would like me to test. Cathode resistors appear to be grounded as far as I can tell. I will check the cathode resistors a...

Ok will do, sorry about that. With all tubes in i get the following readings, also, V4 V5 get very hot and V3 gets medium hot, V1 and V2 stay cooler. V1 - Pin1 452v V1 - Pin6 451v V2 - Pin1 453v V2 - Pin 6 451v V3 - Pin1 266v V3 - Pin 6 453v V4 - Pin 3 483v V4 - Pin 4 482v V4 - Pin 5 -54v V4 - Pin 6...