Solutions to Issues

Here is a link to a good overall amp debugging info (cap47):

There are always a decent amount of similar issues arising among Valveking users. Here are some of the more common issues and there solutions.

Reverb buzz Common
(credit dudey5691)
If you hear a constant buzz whenever the reverb is turned on and maybe even when it is off...
Try jiggling the gray cables connecting the reverb pan to the amp chassis.
DO NOT PULL OR PUSH, lightly jiggle the cables until you cannot hear the buzz.

High-pitched noises coming from amp (feedback, buzz) Common
(credit ...)
Although there could be a million reasons for noises here are a few...
  • Microphonic Tubes (most likely V1 or V3)
    • Do pencil test. Replace bad tubes.
  • Unshielded components
    • Buy copper shielding and shield amp chassis and/or guitar.
  • Your setup
    • Turn down gain.
    • Back away from amp.
    • Make sure all pedals are working and powered correctly/efficiently and have the correct settings (not pushing too much gain).
    • Make sure all cables are in working order.
    • Make sure you are using speaker cables (Head only, or combo-head conversions)
    • Check all electrical grounds (outlet you are plugged into, power strips). Active guitars may need new batteries for pickups.

Tube Rattle (resonating, ringing sound when playing through amp) Occasional
(credit ...)
If you hear a tube rattle, it indicates a loose filament in your power tubes.
You can either deal with it (won't alter tone unless it has been years or tubes have been roughly handled), or replace the power tubes.
*eventually the tubes will need replaced anyway*

Loud noticeable hum in a VK112 that does not go away even with your guitar unplugged nothing in the effects loop and all pots zeroed.

In some VK112s it has been found that there is an excessive amount of hum coming from the amp when at idle
and in run mode ie not standby. The solution is to this is to tighten the nuts around both input plugs and the send/return plugs.
Some VK112s do not seem to have a good ground connection to the case (the case is the ground plane for the pre-amp section)
where these plugs are. There is a small sharp spike on each connector inside the amp that is supposed to dig into the case metal
to create a ground connection. All that is required is to tighten the nuts around the plugs until the hum is reduced. Try not be too rough
with the plastic nuts on these connectors as they can crack if you brute force them. The ideal solution is to open the amp and loosen
all the screws holding the circuit board down so that it can slide forward a bit while you tighten the nuts around the connectors.
I don't recommend doing this unless you follow the directions for capacitor draining on the Warnings page first.
When the hum is reduced to a point that you have to place your ear 2 to 3 feet from the amp to even hear it you have fixed it.

Loud hum on the VK112k (and probably others) that exists on only the clean channel and is unchanged by volume knobs or tone controls.
(Credit to Sadistic_Sponge and 65 SG)
It is likely that the problem in this case is relay switch SK101. A firm tap on it will fix the problem at least temporarily. See full thread for detailed diagnostic information and a link to a compatible replacement component:

Very low volume but everything else seems to be working
(Credit Living Experiment)
DISCHARGE YOUR AMP BEFORE OPENING IT UP: If you don't know what I mean by that, bring it to a tech and pay cash for a repair. It's worth it.
This is an issue I came across after one of my VK112's lived in my trunk all winter. When I plugged it in, it seemed there was no volume. Increasing the volume, I could hear the guitar, but nowhere near as loud as normal. I'd say the volume on 10 with this problem was the same as the volume on 1 normally.
I immediately retubed and still had the issue. I thought it was a solder joint or loose connection with mods I had done previously (JCM800 mod, channel switching mod, and JSX gate mod). In my case I was wrong. It was simpler than that. I had done alot of troubleshooting over 4 days to track down this problem. Below is the solution.
I took out all the new tubes and used a Q-tip and contact cleaner on every socket. While doing this, I noticed the effects loop return jack looked odd. This was the fail point. Nothing was plugged into it, and I could tell the prongs that would normally contact the cable failed to make a connection with the prongs on the side. Removed the jack from the board and replaced with a new one. Problem solved. Hope this helps someone.