New to this site, and tube amp repairs in general, so please be patient and gentle.
A friend gave me his Mesa Subway Rocket to look at. It powers up on standby and remains powered but as soon as you throw the standby switch it crackles for a second and then blows the fuse. Any ideas for troubleshooting or relatively simple fixes? I know my way around a DMM and soldering/rework tools.
One other thing that I noticed was that of the two EL84 power tubes, one glows much brighter than the other. And the dimmer one is considerably warmer than the brighter glowing tube. Again, this is prior to throwing the standby switch. Not sure if this is a symptom or a clue to what the problem might be.
Any help would be greatly appreciated. Thanks!
A friend gave me his Mesa Subway Rocket to look at. It powers up on standby and remains powered but as soon as you throw the standby switch it crackles for a second and then blows the fuse. Any ideas for troubleshooting or relatively simple fixes? I know my way around a DMM and soldering/rework tools.
One other thing that I noticed was that of the two EL84 power tubes, one glows much brighter than the other. And the dimmer one is considerably warmer than the brighter glowing tube. Again, this is prior to throwing the standby switch. Not sure if this is a symptom or a clue to what the problem might be.
Any help would be greatly appreciated. Thanks!
Test the power supply diodes and capacitors, and replace if bad.
Also test the output tubes in a tube tester, and replace if bad.
On standby there's no HV, so it just lights up the tubes' filaments.
Also test the output tubes in a tube tester, and replace if bad.
On standby there's no HV, so it just lights up the tubes' filaments.
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I would bet on bad output tubes. Do not try to get inside the amp unless you are a trained electrician, it might be the last thing you ever do.
Thanks for the warning and I appreciate the concern. I do have my associate's degree in electronic engineering technology (ASEET), but most of my experience is in digital design component level troubleshooting on pcbs. I'm aware of the dangers associated with HV and current. That said, I will test the tubes (I have a tube tester) and the other components in the power supply circuit. I'll let you know what I find out. Thanks guys!
Moved to Instruments and Amps per forum policy.Digital works on a few volts. Tubes run on hundreds of volts, and that can KILL YOU. Be very careful.
I agree, bad power tube is most likely. Pull all the power tubes, now does it blow fuses?
I agree, bad power tube is most likely. Pull all the power tubes, now does it blow fuses?
Me too. Especially the one that is glowing dimmer, but being hotter, is suspect to be gassy and may arc when the plate supply is activated (standby switch thrown).
Be careful: This is a very unhealthy situation for the output transformer!
Best regards!
Thanks everyone. Was a bad output tube. And I was very careful inside the amp. I do have some HV experience, just not inside tube amps. So I do appreciate and understand the concern. Output tubes have been replaced. Amp is running smooth as silk. Until next time!