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?





also to make sure, the diodes should be added at pin 4 and 6 as shown in the second diagram above, with the line on the diode closer to the pin, am I correct?

Yes, I found a picture on the web that show the details

You can solder the diodes on the socket and move the wires accordingly. you can use 1N4007 diode, but UF4007 is better (lower noise) and just cost a few cents more.

BTW, if you interested add on a NTC soft start device please let me know, it just cost less than $20 in parts. Since it will be bypassed in 10 second after power up, it will not affect sound quality. 


wow, thank you very much, that’s a very clear diagram, now I won’t be worried of making a mistake.

yes, I always want to learn more.  Does the soft start and diode compliment to each other, or I only need to pick one to do?

Just like seat belt and air bags, more protection is better, IMO.

However, some might think that put a silicon diode in a tube power supply is a sin! If that’s the case, you can install soft start alone.

The soft start device is a CL-70 NTC thermistor in series between the fuse and the "hot" wire to power transformer primary winding. 10 seconds after power up, a time delay relay which connect to the power transformer 5V winding will turn on and bypass the thermistor. Both items are available on

CL-70 thermistor


Timer Relay Switch Module

Please bear in mind you also have a 3rd option:- capacitor mods.


@imhififan i am in the the-lesser-the-better camp.  So, I think I will try adding the diodes first.  Thanks for the info though.