Laney VH100R repair

  Here 's a nice Laney VH100R tube head that came in. Though it's a nice sounding high gain amp, it hums a lot! That's the main problem of this British rock monster.
  The hum is quite loud and it gets louder on the overdrive channels. So what's causing all this hum?
It's the A.C. power supply of the tube filaments... Laney didn't bother putting a d.c. filament supply or just a hum balance pot like fender usually does. At least, they tried to reduce hum by supplying the first 12AX7 (labelled V1) with dc voltage, but that didn't solve the problem.
  So I decided to put a simple hum balance pot circuit inside the amp plus an EMI filter and it worked! The hum is almost eliminated!  The EMI filter's role is to reduce the noise coming from the 50/60Hz power grid (which is then fed to the valves). The hum balance pot creates a zero voltage(Earth) reference for the filament supply. The hum balance pot has to be rated for at least 2W of power and the Center tap of the filament supply has to be removed! The 5A fuse for the filament supply can simply be removed in this case.

 Here is the original Laney Vh100R schematic:

http://music-electronics-forum.com/t16301/

 And here's the modified one (Open in new tab):

the hum balance 100ohm/2W pot explained:

Here's the Fender 65' reverb deluxe version of the Hum Balance pot:

More info of the hum balance pot: 

https://robrobinette.com/Silverface_Amp_Mods.htm?fbclid=IwAR3nLiG9xNtUGFJNH67ZK1Ki015-yf9pKrOjMMjwnhbQvvwFegiH3J7A9Hw#Humdinger

An EMI power filter:

Pics taken during the repair: