Tube Amp Archive

Sadly the PT was damaged. While I am waiting for a new PT and building a light bulb limiter, I am considering implementing modes to safeguard my amp. Perhaps, the PS-2A being a reactive load might stress the amp. What do you think of the following modes that I found on Rob Robinette's website: 1) vo...

Thanks, I’ll do that.

Update: I examined all connections and re-soldered any connection that seemed fishy. I just tried it again, and it worked! No oscillation and I managed to bias and play. I was super excited and connected the amp to the Fayette power station 2A so I could test it with higher volumes (I can't just use...

The HT fuse, one of the connections.

I can't find a light bulb limiter, where I live. I've connected the resistor between pins 1 and 8 and then to the ground via pin 1 as shown in the instructions. I am not sure that the HT fuse blowing is new actually. It did happen once before when the output leads were reversed. As everything is new...

I meant to say I was measuring on pin 8. Yes, we have a 1ohm resistor from pin 8 to pin 1, and the extra leads from pin 1 are connected to ground. My wiring was a mess and I suspect that it may cause parasitic oscillation, so I shortened long wires and separated them as in the guide. Re-wired and th...

I tried to improve the solder and connections of the capacitors and resistors going into V4 and V5 and then re-tried to bias while measuring mV on pins 5. The values were jumpy, and my hand was pretty unstable. I managed to get both to be around 42mV, plugged my guitar in, and played, and it sounded...

I tested on V4 and got -48V

I finally had time to try it, and it worked! The output leads were indeed reversed. I managed to power on with tubes installed without issues. I started biasing my tubes using the trim pot, and once I continued turning counter-clockwise (after I measured ~35 mA), I got a motorboating sound from the ...

Thanks, I'll give it a try.

I used the fast blow 2A 250V fuses that came with the kit as the wall AC here is ~230V.

So disconnecting the feedback while reinserting V3?

The sound is a screech that increases in amplitude. I tried Using my fryette powerstation as a dummy load and the fuse blew without any sound. When connecting to a speaker cabinet, If I turn the standby by on fast enough I can hear it increasing and I can turn it off before the fuse blows. Otherwise...

Thanks for your reply. I tried powering it on and setting the standby to on without V3 but with all the other tubes, and it seems to work fine. I guess this means that the tubes are fine, and I need to disassemble the turret and start going over all the wirings again? I followed the kit's guidelines...

Thanks for your reply. I checked before I inserted the output tubes, and the voltage on pin 5 for V4 and V5 was -47V DC. I re-soldered most connections on the output sockets and re-checked all the voltages for all pins in the output sockets according to the guide. They are all correct, yet I still h...

Hi everyone, This is my first amp build. I bought the JTM45 kit from Valvestorm and MM Transformers. I finished the assembly and passed all the power-on tests until I reached the output tubes. Once I insert the output tubes and flick the standby to ON, the speaker cabinet starts making scary noises,...