Re-tubing ARC VT-100 mkII

vc69

Hey guys,
I am preparing to re-tube an ARC VT-100 mkII. The sound with the amp has steadily been going "flat" and the soundstage is not what it once was. ARC recommends replacing tubes at 2,000 hrs and I have probably exceeded that. This amp has 8 6550's and 8 6922's. I have several questions for the tube aficionados:

1)I am daunted by the options for 6550's. Are KT-88's a direct and viable replacement tube? If so, can you explain any difference between 6550's and KT-88's?

2)Do the 6922's need to be replaced at the same time, or do they last longer like preamp tubes, which have a recommended lifespan of 5,000 hrs.

3)Can you guys recommend a good brand? Gold Lion? Sovtek?

4)Is matching important when going with all new tubes? Should I have them matched in Quads or Octets? Will this affect my ability to easily bias the amp once the new tubes are installed?

This is no small expense and I would like to get it right. Of course, ARC wants to sell me their tubes but they seem a little high compared to ordering from Tube Depot, etc. I plan to talk to these folks (ARC, tube dealers, etc.) but I would like to be armed with some knowledge going in.

Thanks in advance for any help or suggestions. I look forward to hearing some advice.

sucks2beme

Buy a matched set of 6550c winged "c" tubes. Be careful, the company split
and the name went one way, the winded "c" logo went another. Go with the
wings. The 6922 tubes do last longer.
Note: the whole 2000 hour thing is really overkill. But changing tubes before
they pop and kill other stuff is a good idea. Please check the bias setting to
make sure your not a simple turn of a screwdriver away from good sound.

vc69

Thanks for the reply/info.
I biased the amp just a couple months ago, but I will revisit just to be sure.

sucks2beme

The great thing about arc stuff is you can run current, quality power tubes
and sound great. you can then do your fine tuning for sound using the 6922's.
Much cheaper to fool around with than NOS power tubes.

vc69

So there is a big difference in the 6922's? I have whatever came stock in the amp. Any recommendations where those are concerned? Some of those NOS tubes are extremely expensive. Are any of the current production tubes worthy?

zingo

I have many quads of 6922 tubes that I was planning on putting in the Flea market soon. Usually tubes should run in pairs (one for each channel), so I assume that if you need eight tubes, four pairs or two quads should work well. PM me if you are interested.

The Gold Lion tubes are great, but are more detailed than warm if that works with your system. The best new tubes for that variant in my opinion, but not cheap.

sucks2beme

That depends on what you thought of the sound up to now.
If you liked it, stick with the same. Warmer, detailed, etc. are changable.
A quick run over to tube depot or others, read up, and then search here by
brand/series to pick one. Warning: this is normally the start of the "tube stash"
that keeps growing in back of your closet.

doctor r

If you decide to look at the KT88 tubes the KT88sc is marketed through Penta Labs (Doug's Tubes sells them as well as others). These solid plate tubes are what performs best in my VAC amps IMO.

Rick

vc69

Thanks Rick, and everyone else that has replied. I have tracked down a connection to a guy that works for ARC and as soon as I get some info from him, I will pass it on here. I am anxious to hear what those guys have to say regarding tubes recommendations, matching, brands, etc.