Advice on Repairs for Audio Research VT100 Mk II

ARC amps are built well and tend to be reliable. Until they're not. I believe most ARC experts and fans will admit that there were some clunkers along the way, in terms of sound, design and reliability. I had a VS110 (which was the lower-tier amp contemporary of the VT110 IIRC) that was remarkably reliable for ten years of constant usage. 

Most-but not all-tube amps are expensive to maintain. My ARC Ref 150SE uses eight KT150's. That means paying $1600 or more every three years more or less to re-tube just the power tubes, closer to $2800 if you opt to buy ARC's "specially screened and matched" tubes. 

I don't know this particular model, but had ARC gear for decades- multiple amps, preamps. I still have the Dual 75a that I bought new in 1975-- it is sitting idle with a fresh tube set I bought from ARC a number of years ago. They were never cheap to maintain but I did get a lot of utility out of them. One question I would ask given the price is what kind of warranty you can expect after having paid to replace all the tubes and associated resistors? I used to deal w/ ARC in Minn. and they stood behind their work. That was quite a few years ago- I don't know what difference it makes that you are dealing w/ an authorized facility in another country or how things may have changed given that the company is in different hands and the amp is relatively old from what I gather. Typically, warranties on tubes themselves are limited, but....

I still run tubes, and periodically have the manufacturer go over the amps, line stage, phono stage, etc. There is a running cost to these things-- I like the DR variant of the 6h30 which, for a vintage quad (used in my line stage) is not only costly but very hard to find these days. Generally, I've found tube gear of this calibre to be pretty reliable other than routine maintenance, tube replacement but cannot speak to whether this particular model is worth investing in for the long run. If it is, bite the bullet, get it done and enjoy it! 

@edward78

The VT100 MK II first came out in 1998 though 2000, (maybe through the spring of 2001). The amp is at least 21 years old. I am surprised the Tech that gave you the price for the repairs didn’t mention that. How about the electrolytic caps in the power supply? They are probably original. They may still be ok and last for many more years. But... I would suggest you call the Tech and ask him what it would cost to replace the caps.

https://www.arcdb.ws/model/VT100

If it were me, I would lick my wounds and move on and caulk it up to experience learned... You will end with a whole lot more money in the amp than it is worth.

FWIW, there is a very good chance the guy you bought the amp from knew the amp was ready for a complete re tube.

..

... As to the burden if an issue comes up later, the shop will bear this burden for only 6 months, which is the guarantee they’re offering. It’s better than nothing, but not exactly confidence inspiring ... this amp already feels like a liability ...

Six months is actually a reasonable warranty for used equipment repair, especially for vacuum tube gear.

I’m sorry for your grief but it sounds like tube gear may not be for you. @jea48 may be right that the best thing for you to do is move on.

I love the sound but the amp has needed two repairs within the first 6 months, so it's really put me off the whole tube amp thing.

@edward78 FWIW, there are tube amps out there that don't require resistor replacement (which might mean a trip to the service shop) every time a tube fails!

IMO/IME this is a design thing; it is possible to calculate how much wattage the resistor needs to be rated for when a tube fails and does its worst- its not rocket science. Some manufacturers have sorted out this issue and some haven't.

When looking at a new or used amplifier, its a good idea to ask the manufacturer "what happens if a tube shorts out- what damage (if any) will it cause?"