Is rectifier tube arcing a problem?

If this is "only" happening when you power down one of the amps and then restart it within a very short period of time, just wait longer (5-10 minutes).

If it happening @ other times, then it needs to be looked into.

I would not reuse a rectifier that I observed arcing, but I've always had plenty of spares.

I found a schematic of the power supply section @ the Steve Hoffman Forums, but could not link it.

I Googled your amp + rectifier and it came up on the first page of hits.

DeKay

Add a negative temperature coefficient (NTC) thermistor on the primary side of the power transformer and bypass it with a time delay relay may help.

Short answer is Yes, the arcing happens in both channel.  
 

for the 5C3S, at the beginning, I don’t think they arc.  Then after a month, both tubes arc.  For the RCA, they both arc right the way.  For the TungSol, so far, only one arc.  And when I switch the tube, same behaviour.  
 

maybe as you say I have bad luck, but the percentage seems too high, 50% or 3 out of 6 pairs arc.  That’s why I think could it be a me doing something wrong which cause this.  But there is only one button, I can’t think of anything except I didn’t wait long enough when restarting the amp.  
 

is it very common for 5U4G to arc?  I only have two amps that use 5U4G, and I didn’t roll the tube in my previous amp.  

@atmasphere and others

BTW, is there other rectifier can be used for this amp?  Such as a soft start 5AR4?

From what I gathered surfing the WWW 5U4G is the only rectifier recommended for your amps in stock form.

I've only come across them with guitar amps of which a few local guys preferred the 5U4G (over the GB version).

This is of course apples to oranges as far as your AN's go.

Try and find the thread (threads) @ the Steve Hoffman Forums pertaining to your specific amps as there were gobs of posts/pics/info that I did not read through in detail (including power supply/slow start mods).

As they are kits I doubt that well thought out modifications would decrease their resale value down the road.

From the few pics I viewed they looked easy to work on (unlike my old Audion 300B amp that resembled the innards of my TV7 tube tester;-).

I would start by confirming that your units are actually built to the original AN specifications and then go from there.

Yes, it's possible that your old production tubes are duds as I've always found rectifier tubes difficult to test with my old TV7/Hickok 539 testers in that they always tested good until they didn't (same thing with 12ax7 tubes on the same testers).

DeKay