Tube Amp Archive

dr. who wrote: ↑Thu Oct 16, 2025 11:56 pm Emergency meetup?

Like for the day you can no longer access this forum. Maybe you just bought $500 worth of stuff from me, but now I don't know where to send the stuff. That could be an emergency.

For a good start, read this...

https://www.valvewizard.co.uk/smoothing.html

That PT is not a replacement for his PT. His original PT has a much lower HV winding without a center tap and is meant for a full wave bridge rectifier. This "replacement" is for a conventional full wave rectifier. However, the white wire may still be a center tap for the heater. But since joe has n...

I have 212VDC on the plate, I have 14VDV on the grid and 47VDC on the cathode..... I would think that the voltage on the junction of the 1.5K(45VDC) and the 56K should be present on the grid. Those voltages are fine. This PI circuit uses bootstrapped biasing which is high resistance. Your meter act...

Check for continuity between the white wire and all the other wires. Then tape off the white wire.

Thanks for setting me straight Stevem. I saw 2204 and automatically jumped to JCM-800 2204 without realizing there also was a JMP 2204. :oops: I apologize for my ignorance. I finally saw the mojo schematic for the 1976 2204 and there is indeed a 330K on the V2 socket. Here's the original Marshall sc...

All your voltages are low as compared to the mojo schematic. Look at the attached schematic. Post the measured B+ voltages at points XA, XB, XC, XD, and XE. Also measure the resistance of the three 10K dropping resistors on the B+ rail.

All the wiring is correct but the 330K should be 100K. So, just replace the 330K with a 100K. Don't change anything else!

Lower the screen voltage to bring the current down.

Lower the screen voltage to bring the current down.

Back in 2006, after a 30-year hiatus from amp building, I renewed my interest and stepped back in. So, I bought three Hammond 1444-20 aluminum chassis because they were a perfect fit for a 5E3 combo amp. These chassis were 17.00 x 4.00 x 3.00b but only .04" thick! That's less than 1/32"! Machining w...

Roe wrote: ↑Wed Oct 01, 2025 9:32 am Is there any way to upload a pdf here?

Easy. Look below. May have to scroll down a bit.

Thanks; there is no 6N7 on the unit I am servicing. See my schematic. There is "infinite" resistance at the grid of V3 to ground, on mine. That's my mistake for looking at the wrong schematic while typing. Of course I meant your V3 grid that is floating. This is against everything I was taught abou...

Hoffman sells blank boards for $2.50. He also sells matching power supply boards, as well as all components to populate these boards.

https://hoffmanamps.com/MyStore/perlsho ... =!ORDERID!

With both volume controls set max CCW, measure resistance from chassis to pin 4 and pin 5 of the 6N7. Connect the meter directly to the tube socket. What have you.