Tube Amp Archive

Thanks for that, appreciate your knowledge. Hopefully it's not as dire as it sounds. If you have driven high level audio signal thru a fully working amp, but with the secondary side of the OT feeding into no load ( as in a open circuit ) then there's a real good chance you have caused a arc over of ...

I put a radio signal through and found the OT is making noise, but not the speaker. What do you make of this? https://drive.google.com/file/d/1DLqZ8X ... C-pQ0lYBFQ

Ok had some time today to progress this. Voltages were all over the place. Swapped out the rectifier tube and it settled down (5U4 tube; 290BEX has current of 3A, so should be fine). Put a radio signal through and i can hear some sounds - possibly from the OT, but not the speaker. Back to Robinette'...

Once that is straightened out, you might find things a little bassy. If so, cut the value of the input Rk from 20uF to 4.7uF. And the coupling caps from 100nF to 22nF-47nF. At least that's what mine needed. As it's a harp amp, the "bassiness" shouldn't be as much a of an issue. I built a 5f2H previ...

How are the batteries in your meter? Sometimes low battery state can cause bizarre readings. Well, that was a good steer - 9v battery measured 5v! With new battery and tubes in place, the new values measured are alot more sensible ( https://drive.google.com/file/d/1asZqOt88zeziY-g3PWppaoz_P2ERNP-n/...

Yeah, it's a second hand OT. Previous owner had trimmed them short on the exit and then added extra length so they could enter the chassis. Red is correct, the black wire is an extension of blue and red/yellow is an extension of brown. Red to blue (black) = 204 Red to brown (red/yellow) = 205 Blue t...

No worries. Pwr section https://drive.google.com/file/d/1VSYMfCnYlmM9cGrjIxOtKaTOuw3gPOTI/view?usp=drivesdk Pre amp https://drive.google.com/file/d/1qAYs2R8fbiW67nzZVlvDF5kTkkasM315/view?usp=drivesdk Inputs and controls https://drive.google.com/file/d/1M0vOxl9EXt66KOs4FT_-N1cEmzlBdkLS/view?usp=drive...

Thanks Martin. Yeah, 252.1 Ohms from 6v6 (v3) to chassis and 254.0 from 6v6 (v4) to chassis.

I’m at a loss for why the difference too. Appreciate your thoughts. Cheers

Thanks for your reply.

No tubes installed.
Rectifier
pin4-chassis =363
Pin6-chassis=363
Pin2-8=5.2

I didn’t measure cathode voltage as I saw the excessively high voltages, so paused further investigation to find out how to address. I can check if it helps?

Hi all. An update and request. I've finished the build and started up (layout and initial voltages attached). I'm using a Hammond 290BEX power transformer and 1750H output transformer. I've found I'm getting no sound and 785v on pin3 of 6v6 plates :cry: (no red plating though). I've checked all sold...

Hi there, I'm hoping for some reviews of my schematic - any advice appreciated I'm building a harp amp based on a 5c3 and 5d3 Deluxe - keen on trying out the grid bias from the 5c3 (for crystal mics on channel 1) and paraphase inverter from the 5d3. Channel 2 is more based on a 5f2 input (but likely...