@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).
I found that thread at the Steve Hoffman Forum. Honestly, what being explained there is beyond my technical knowledge. I like the idea about adding a soft start, but I need to take it to my tech to do that. But do you think adding a soft start will eliminate the arcing?
Some/most of it is beyond my tech knowledge as well, but I do understand the basics of it.
I've relied upon techs/friends to update my tube gear in the past and I gleaned a tiny bit of understanding from doing so
This would be good info for your local repair person to read/consider.
Until 10 years ago I did not know what the tiny transformers a friend installed on my Dynaco ST70's, being used as mono blocks, were for (power supply chokes).
He performed the modifications in 1979, and said that the stock mono/stereo switch/circuit was a bad joke.
The improvement in sound quality from the mod was not a slight one.