Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: slim66 on June 02, 2026, 09:33:19 pm
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I'm a newbie, and I built a standard 5E3 circuit. It sounded glorious through the P10R in my original 5E3. But then I decided to switch out the wire to pin 2 of V2 with a shielded wire, just to try and make it a little quieter, and the amp has been dead ever since. I looked under the board to make sure I didn't accidentally pull out a jumper. All components measure correctly. I put the original wire back to pin 2. I am getting crazy voltages to both 12ax7s.
V1:
pin 1=293V
pin 3=20.3
pin 6=292
pin 7=0
pin 8=19.9
V2:
pin 1-292
pin 3=0
pin 6=240
pin 7=23.4
pin 8=56.3
I have no idea what to do, other than rip it up and start over. I've changed tubes, I've re-flowed solder joints. Not sure how I blew this thing up so badly.
Any insight would be appreciated.
Thanks,
Slim
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I can see V1 voltages are out of whack.
You should be reading under 2V for pins 3 and 8.
V2 it looks like one triode isn't conducting.
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V1:
pin 1=293V
pin 3=20.3
pin 6=292
pin 7=0
pin 8=19.9
V2:
pin 1-292
pin 3=0
pin 6=240
pin 7=23.4
pin 8=56.3
I can see V1 voltages are out of whack.You should be reading under 2V for pins 3 and 8.V2 it looks like one triode isn't conducting.
Use your ohm-meter to heck the shared V1 cathode resistor value on V1 = Should be about 820 ohms. If this is in the ballpark, then you may not have the V1 plate resistors hooked up properly. You should be seeing about 100V dropped across each plate resistor (between each plate and the B+ node for the pre-amp filter cap). If you have somehow connected the plates directly to the B+ rail, that could explain a 20V across the cathode resistor
On V2 Pin 3, check you have the requisite 1,500 ohm cathode resistor hooked up between the ground and Pin 3. If this is wired properly and you are still getting 0V on Pin 3, it could be a loose socket pin clamp for Pin 3 - or it could be you have a dud 12AX7 (which seems less likely).