Rectifier Arcing Problems When Switching Amp Modes

https://www.youtube.com/playlist?list=P ... F23jLjEpOC
Post Reply
bigchips
Posts: 2
Joined: Thu Jan 06, 2022 2:47 pm

Rectifier Arcing Problems When Switching Amp Modes

Post by bigchips »

I am having an issue where my 5AR4/GZ31 rectifier tube arcs and destroys itself when switching between ultra-linear and single ended mode. First, the 2 amp slo-blo fuse blows, then when I replace it and power it up the rectifier tube arcs and destroys itself. I have now lost 3 tubes to this phenomenon (2 Sovteks and 1 Gold Lion) and it has happened when switching both directions (to and from). I have never completely drained the capacitors, but I have always waited between 2 and 10 minutes or so between switching modes to let the tubes cool down. If I leave it in ultra-linear mode then I have absolutely no issues. The arcing either happens when first going to single ended or when coming back to ultra-linear. So this happens very quickly and not randomly.

Anyone else have this issue or know what could be causing this? The only modification I have made is removing the grid stopper resistors on the preamp and power amp tubes but I think this happened once before I made this change. Huge soundstage upgrade btw and I don't want to have to put them back. :)

Any thoughts? I am not using a thermistor or anything like that.

Brett
Simonism
Posts: 4
Joined: Thu Jun 03, 2021 11:23 am

Re: Rectifier Arcing Problems When Switching Amp Modes

Post by Simonism »

Brett

There's a great thread on this amplifier on Audiokarma, and it goes into this issue in a bit of detail - see here, post #1352 and onwards into later pages: https://audiokarma.org/forums/index.php ... 77/page-68

I had similar issues to you (with switching on, especially when warm and the sun was bright on my rooftop solar), and I seem to have resolved them by adding a 10 ohm resistor and halving the capacitance in the power section. I also have a bleed resistor to ground (through a 'tell-tale' LED) on my B+. All in the AK thread ...

Hope this helps you work out your issue.

Simon
bigchips
Posts: 2
Joined: Thu Jan 06, 2022 2:47 pm

Re: Rectifier Arcing Problems When Switching Amp Modes

Post by bigchips »

Huge thanks Simon! Dropping the capacitance to 100uF seems to have solved the issue. I have tested with 3 different 5AR4's and no issues going back and forth (letting rectifier cool down between switching). Much less transformer hum as well on startup which I would assume signifies less current draw. Dropping the capacitance had no perceivable effect on the sound and definitely opens up some possibilities price wise for higher quality caps.

As a bonus, here is my order of preference on the 5AR4/GZ34 rectifiers I have used:

1. Gold Lion <- Best all around with best sound stage and separation between instruments
2. Sovtek (Tube Doctor just rebrands this btw) <- Not bad but definitely prefer the Gold Lion's better bass and sound stage
3. JJ <- Very mellow with a lot less detail and emotion - Can't say I recommend this one at all


Brett
Post Reply