Is rectifier tube arcing a problem?

I did some research and couldn’t find a definite answer.  I have an amp that I tried 6 different pairs of 5U4G and 5U4GB. 3 pairs has arcing (RCA 5U4G, TungSol, Svetlana 5C3S) and 3 pairs don’t (RCA 5U4G with hanging filament, EH 5U4GB, Sylvania 5931).  I took the amp to a technician and he checked everything, he can’t find anything wrong.  The problem is, I like the sound of the TungSol and Svetlana which both have arcing.  The technician said it is ok to keep using them, but honestly I am not too comfortable.  But I like their sound.  Is it really ok to keep using the arcing tubes?  Will it damage the amp?




@atmasphere @imhififan 

Yes, mine also has 220uF capacitor, and yes, the arcing only happens when the amp is turn on. After than, and if the fuse doesn’t blow, the amps sound fine.

here is the wiring diagram of the capacitor and resistors.

Wiring Diagram

Besides adding diodes, is there other recommended options about changing capacitors or resistors?  But I guess changing capacitors and resistors will have a bigger impact to the sound, right?

Yes, mine also has 220uF capacitor, and yes, the arcing only happens when the amp is turn on. After than, and if the fuse doesn’t blow, the amps sound fine.

Nailed it!

I would replace the capacitors after the choke with 50uF devices rather than the 220uf units. If anything you might hear a slight improvement since the smaller cap might perform better at high frequencies, if you install ones of similar quality. If you do this there may be no need to install the solid state rectifiers, although the caps in succeeding legs of the power supply are gross overkill (contributing to rectifier failure) as well. You could run 1/5th the value and be fine.


thank you very much. A couple more questions:

1) is it able to tell from the diagram if there other rectifier that can be used and handle the current drawn by the 220uF capacitor?

2) is it necessary or recommended to change the other two capacitors? If yes, what values should I use?

3) comparing to adding diodes, in your opinion, which way will yield better sound?


IMO, reduce the capacitor value will has a bigger impact in sound quality, those 220uF capacitors are mounted into a 35mm clamp with point to point soldering. You need to find a 50uF cap with similar quality and diameter to fit into those clamps or you need to find a way to mount them into the chassis if the caps has different dimension. And the modification cannot be easily reverted!

OTH, install two UF4007 on the rectifier tube socket is a very simple job ( it takes less than 10 minutes ) and those diodes only cost a few dollars. Its also very easy to reverted.

Those diodes are functioned as a protection device to reduce the chances of rectifier tube arcing and also can prolong the life of those rectifier tube. BTW, the effect in sound is negligible.

My suggestion is go ahead install the diodes first, put in some new rectifier tube and see if it solve the arcing problem. If you don’t like the result, then go for the capacitor mods or install soft start device.

BTW, always wait as least 5 minutes to let the tubes cool down before you switch the amplifiers on again as @dekay suggested.




"Finally, some real help for this problem. Thanks for helping to solve problems that the wannabees simply cannot."

You have contributed nothing useful to this thread (instead you have performed as a cheerleader with your +/- opinion of those who have contributed useful info/avenues of thought).