Tube amp repair.

Brian,

Ralph Karsten (Atmasphere) does repairs. He is one of the nicest individuals in audio. I am sure it will be a piece of cake for him. His office is on Selby Ave. in St. Paul. Also, Hi Fi Sound in Minneapolis (near farmer's market) have a technician who repairs tube equipment.

They both have web sites.

Good luck,

LectronJH50

Give up and face the fact that D is better 

I replaced the 4 power KT88's with a set of Gold Lions and of course I checked the bias. As far as the variac is concerned, many Chinese amps and also older designed US amps are designed to run on 110v. Most Wall sockets today are 120v, tho this may be vary some depending on where you are (mine runs from 120v to as high as 125v. I have talked to several techs over the years who say these types of amps should always be run with a variac to keep the voltage under at least 115v. 

Is there a bias adjustments on each side. The desired voltage is written on the side 2V. There should be pots for the 6SN7 too. They are under the plate. Check the bias first, then it's most likely a bad valve. They have a soft start circuit, no need for a variac. Few newer valve amps require a variac. Most of the older ones if they have been worked on at all, something has been added to aid in a softer start.

Regards

I had a Yaqin MC-30L amplifier that world flawlessly for me for several years and a friend of mine has it now.  I think Yaqin is above the Chinese "junk" stereotype, but repairs can still be expensive.  My local shop (across the country) charges around $200 per hour for repairs I believe.

I'd check with some of the local hi fi shops as they may have a person that does their repairs.

Two questions. Why do you need a variac and why don't you think it just needs new tubes? 

Could well be.

New Chinese amp will be cheaper. That's how it usually works with Chinese gear pretty much anywhere.