Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TF2112 on May 26, 2023, 09:43:07 am
-
Hey y’all! I am putting together a 5f1 and I have 80 volts to ground on the hot side of the switch with my meter with no load. I have 365 on the high voltage b+ and all my filament voltages are correct. Is this normal? Thanks.
-
Hey y’all! I am putting together a 5f1 and I have 80 volts to ground on the hot side of the switch with my meter with no load. I have 365 on the high voltage b+ and all my filament voltages are correct. Is this normal? Thanks.
No. There should be 120vac from the switch to the chassis. This assumes you have a 3 wire power cord with green wire connected to chassis ***AND*** your house wiring is also correct with grounding outlets.
-
I assume you mean that your DVM is reading 80V(rms) on the side of your mains switch attached to your fuse, with the mains switch closed.
Assuming no Variac or LBL in front of the amp.
In other words, you're saying that your mains voltage is 80VAC, and your B+ is 365VDC?
Something isn't right. Could be my assumptions, my interpretation of your data, could be operator error, or -- less likely -- an actual fault in your amp.
-
The fact that his filament voltages are correct indicates that he has 120VAC between hot and neutral, but there is a grounding problem in his amp or house wiring or both. Heck, he may only have a two wire system or power cord.
-
Thanks for the help y’all. Yes my house is 100% wired correct. I am using a variac but the voltage on its receptacle is 123 volts.Okay with all the tubes in I am getting these voltages. 396 on b+1 350 on b+2 295 on b+3 195 on the coupling caps and 21 on the power tube cathode. Still getting 80 volts from chassis ground to anywhere on the power coming in on either side of the switch or either side of the fuse. I just noticed while writing this that if I plug in my guitar to the high input I see a faint arcing in the 6v6. I am using a Hammond Pt290-ax power transformer with the 325-0-325 windings and the 6.3 center tap for the filaments, and a pt1760c output transformer at 8k@8ohms with a rca speaker jack that is chassis grounded to a Weber 8 ohm 10” speaker.I am using a brand new jj 6v6s an older sovtek 5y3 and a really old fender 12ax7 to test. Wish I had a tube tester to rule them all out. I do have a 3 wire power cord grounded to chassis as well. Thanks again!
-
The correct way to measure the line voltage at your amp is to connect meter neads between the black and white wires of your power cord. Don't measure between black wire and chassis.
Do you have a three prong power cord and is the green wire connected to chassis? If so, plug the power cord directly to the wall outlet. Can you measure 120VAC between the switch and chassis now?
-
Well my dumbassery knows no bounds. As soon as I unplugged from the isolation transformer it is all good. I apologize for wasting anyones time. Still worried about these high b+ voltages though now I have 430 370 316 on the b+ nodes 205 on the coupling caps and 23 on the cathode. And I wired it where I solder the neutral to the primary and heat shrinked it.