The Amp Garage

Martin, I will try bigger resistor .
Marcus, my buddy is also building the same amp, so he wanted OD on a foot switch.... so good idea thanks

I am running NOS NEC 6v6GT’s and I haves another matched set available. I thought the consensus with this build was to run them on the edge of a cliff? 😉. Some have posted 17-18w dissipation!! I could buy a set of JJ’s 😏. If I “cool” it down..., must I do so with the cathode resistor value or just ...

I am running NOS NEC 6v6GT’s and I haves another matched set available. I thought the consensus with this build was to run them on the edge of a cliff? 😉. Some have posted 17-18w dissipation!! I could buy a set of JJ’s 😏. If I “cool” it down..., must I do so with the cathode resistor value or just l...

Thank you Martin!!! The junction of the 2x 220k resistors was not properly grounded. I had not stripped the wire (under the board going to the earth bus) properly. Redone connection and amp sounds fantastic! Really chuffed 👍👌. Thanks to all here on TAG for taking the time to reply. Plate to cathode ...

Thanks Martin, I think I can “see” where I *^%*@# up! I will check when I get home tonight and report back. Just looked at the schematic again. I bet you, I left out that 220k junction to ground un-grounded

Yip Martin, on both pin 5’s. One is slightly higher than the other.will check the caps for leakage. They were all NOS 6PS from a set meant for an express build. I think I got the whole set from one of our members here.

Leave the cathode resistor as it is; you don’t want it running any hotter! Power up with the output tubes removed and measure voltage on pin 5. Should be zero or very close for a cathode biased power stage. Will do. However, I have already reverted back to the 250 ohm cathode resistor. I did briefl...

Leave the cathode resistor as it is; you don’t want it running any hotter! Power up with the output tubes removed and measure voltage on pin 5. Should be zero or very close for a cathode biased power stage. Will do. However, I have already reverted back to the 250 ohm cathode resistor. I did briefl...

Ouch! That's hot! What is the measured voltage on pin 5? I will install old tubes and recheck. Should I go back to the recommended 250 ohm cathode resistor? One thing I did notice was, the B+ would go to 380v once the rectifier starts to conduct (about right for a 315-0-315 PT after FWB). Then as t...

I’m in trouble and need help!! Brought amp up on variac first and did some measurements. At a B+ of 290v, I get a plate to cathode of 245v! So...I also get a voltage drop on the cathode resistor (320 ohms) of 46v!! Without the variac, I get 340 B+ and the cathode voltage drop is 57v!! Surely this is...

Thanks Marcus. I play a Express normally, however, it is loud . I don't use pedals, only guitar knobs. The previous Tweedle I built sounds great, but looks like a dog , so decided to try building “proper” one which is more small club friendly

More progress. Finally finished wiring the amp. Will do wiring check for the 10th time and then its time to fire her up. Any glaring mistakes, please feel free to chime in. Added the “cascade gain mod”, ala Robibrite.

Here you go from the service manual.

I am sure I saw somewhere, that the PT was 160ma and 315-0-315. Will look for it

Thanks Mark. I have been playing my Express exclusively for the past 2 years, but really enjoy this circuit. The type and size of venues we get to play at, really suits a small combo you can drive. I play the express with a VVR installed.