Advice on Repairs for Audio Research VT100 Mk II

Op,

I definitely understand your dilemma. Honestly, I think the repair estimate is absurd. thirteen hours.

Also, calling ARC is in no way “going behind your repairman’s back”. That is an absurd quote. 

Audio Research makes some of the best amplifiers… regardless of the technology. You are talking about a 20 year old amp. A couple repairs and it is obviously got problems.

I would not loose faith on tube amps, or Audio Research for that matter. I have owned quite a few Audio Research components over the last forty years and have gotten. Nothing but incredible sound quality and reliability. I would get something more contemporary. I own all Audio Research equipment, and have enjoyed their sound and reliability for decades.

Owners Manual for the VT100 and VT100 MK II.

https://www.arcdb.ws/Database/VT100/ARC_VT100MKII_manual.pdf

Note, page 1:

Diagram indicates relative positions of all (16) tubes on the two circuit boards as viewed from the front and looking down from above the amplifier. 

Next go to page 2:

2) ........ match its location "V' number (written on the base of the tube) to the "V" number printed next to each socket on the circuit board. (see accompanying tube location diagram.) Firmly seat each tube in its matching socket.

Next go to page 4:

Output Tube Bias Adjustment

Note, no mention of the input and driver tubes Bias Adjustments.

Just a guess most of the VT50, VT100, VT100 MK II, and VT 200 amps were damaged by their owners when they bought their own tubes and did a total re-tube of the amp. If the owner only replaced the power tubes there was no problem... Problem was when the 6922 tubes were replaced... Nothing in the owner manual about needing to bias the 6922 tubes. Just the output power tubes needed to be biased... Problem is if the new 6922 tubes Triode sections were not tightly, closely, matched and the new tubes were not biased to ARC specs, (especially the driver tubes), damage to the amp will be the result. and sometimes the damage is extensive.

.

Did you or the guy you bought this amp from install new 6922 tubes in the Amp?

Or maybe did the guy you bought the amp from pull all the tubes from the amp for shipping? If yes each tube would have to have been marked for each tube socket they were removed from and reinstalled in the same tube sockets they were removed from...

Thanks again to everyone who responded. The tubes were already installed when I bought it and I had a car share and a short drive, so I didn't bother removing the tubes for the drive home. I think he said that the tubes were fairly new. It was my first tube amp, so I didn't know which questions to ask. The former owner is actually really helpful and offered to help pay for the repair if I get the work done at the tech shop here in Berlin that he regularly uses. I however wanted to get it done at the authorised dealer in Hamburg, which he considers to be overpriced.

Some responses above have suggested eating the costs and moving on, but that would mean selling the amp as defective and I wouldn't expect to get more than EUR 500 for a defective amp. That would mean a loss for me of EUR 2,000. Or do you think I could get maybe EUR 1,000?

So, at this point I think I will either bite the bullet and get it repaired at the ARC authorised dealer or have it sent back from Hamburg (which is another EUR 100) and get it fixed by the tech guy here in Berlin recommended by the former owner. I just don't feel like lugging this beast around any more. I don't have a car, so moving it always entails doing a car sharing or taxi/Uber.

I also sent an email to ARC as suggested by some of the posters, so we'll see how they respond. 

Since you mention that it is your first tube amp I want to mention that hopefully you are aware that you should not turn a tube amp on and off and back on quickly without giving the capacitors a couple minutes to discharge.  That can lead to problems such as you describe.

According to the schematics the VT 100 MKII is a fully balanced design. The offset between pos and neg branch needs to be set to 0 and that's taken care of by some ss circuits between the 6922 (some adj. can be made with RV1/RV2 trim pots).

The 6922 are double triodes and it's of course harder to match those tubes because you need a lot of them in order to find 4 tubes per channel where the two triodes in each tube are also about the same quiescent current. That makes it time consuming and expensive. In general Audio Research biases  their output tubes very hot and they need a lot of tubes to select from in order to reach those goals. That's why it is so expensive if you go to Audio Research for retubing.

Many things can go wrong if one tries to do this buying tubes (even matched) somewhere else unless one fully understands how this amps work. Schematics are available online.

To use the VT100 only makes sense IMO(considering the high cost) if one uses  a fully balanced system (at least preamp to amp).