retube VTL amp

Purchasing tubesets from the amp manufacturer will generally mean overpaying, which can amount to a lot with amps having as many tubes as these.

The SED 6550C is VTL's stock output tube for these amps and a fine choice, though I've also liked the results from using the drop-in compatible Electro-Harmonix KT-88EH for a less-'tubey', cleaner sort of sound (I haven't yet tried SED's own well-regarded version of the KT-88, nor the JJ/Tesla some have spoken highly of). Based on past experience with other power tubes I'd avoid the cheaper Sovtek or Chinese versions, but haven't heard those 6550's/KT-88's specifically.

The 6350 drivers are normally available made only by US Sylvania and are not costly.

Those are the tubes you should replace at 3-5 year intervals due to wear (depending upon use). The input amplifier 12AT7's may last longer than the driver and power tubes, but here it can pay to experiment with premium NOS varieties, as none of the newly manufactured examples are as good as what used to be made back in the day, and this tube is very deterministic regarding the overall character of the amps' sound.

But I won't open that can of worms here (you should do a forum search on the subject), and if you just want an inexpensive 12AT7 to drop in and see if the performance of your existing input tubes can be improved for the time being, I would recommend the commonly available US JAN Philips/Sylvania/GE varieties or Yugoslovian EI's over the current Russian, Czech, or Chinese versions.

The best pricing I've found on the more costly and numerous power tubes is at Triode Electronics Online, while the EI input tubes are sold at TubeDepot.com. BTW, this is just my experience, but I haven't found it cost-effective or failure-preventative to pay a premium for new power tubes from a reseller charging extra to burn-in, pre-test, and match the power tubes beyond what the Russian tube factories already do as standard. (Close output tube matching is not needed with the VTL's individually-adjustable bias trimpots, though your input tubes should be bought as matched pairs to ensure an even gain balance between channels.)

Before installing your new tubes, remember to turn the bias pots on the output tubes all the way down first, then turn on the amps and let them warm for a few minutes, then gradually bring tubes up to spec on the meter as the they continue to warm, rebias them again after 10 more minutes, and then again 30 minutes later, plus check them again after 3 days and once more at 2 weeks, by which time they should have stabilized enough to only need a check every 2-3 months or so.

Zaikesman covered everything very, well.

I just got my first tube amp last year, and started rolling.
Both the places he mentioned were at the top of everyone's
list for good service at a fair price.

So far I've only ordered at the TubeDeopot, one power tube
blew at about 5 weeks, I sent it back and they exchanged it.
Joe was nice to deal with.

You will probably save a few $ on power tubes at Triode if you don't need them bias matched ( I think they charge $1.25 to match), TubeDepot matches all power tubes standard, but you will pay a bit more.

I have Manley Reference 350's.

Be glad you ain't got KT90's Schieza. The good one's are no longer made, but Kevin Deal tells me the new EH version are a little more lively, hmm what does that mean.

Tube dealers, Kevin Deal, or jim McShane are good choices, you know what your getting and they stand behind them.

I am toob rolling again. The current NOS Phillips @ about 5-10 each depending upon whom you buy them from are pretty good. Better than stock VTL.

The Sylvania's the old one's, I don't like as much as the newer ones. I am finding that more and more. I am not a fan of the Chineese tubes I've heard yet.

Mullard as new, as in new 6550's out. They are new on the market and pricey. If you can hold out a couple of more months those will drop in price like a rock.

I have a new set of 83 vinatge Mullard 12at7's that came in yesterday. $13 each. I will roll those, and give me a day or two to listen and I'll tell you what I think.

loon

I made a rather large omission when I forgot to point out that although the 12AT7 input tubes may not wear out in the electrical sense as quickly as the driver and power tubes do, they are subject to deterioration in the area of microphonics, a problem which if it develops can severely compromise the overall sound of the amps. More than once has been the time my VTL's began to sound vaguely disappointing compared with memory or a solid state reference amp, but still it might take several days to dawn on me that the input tubes had started to exhibit audible resonances - D'oh! Replacement with a quiet pair immediately tightens everything back up and eliminates the creeping sensation that the presentation is beginning to sound confusingly frayed rather than solidly wholistic.

You can check these tubes simply by tapping gently on the glass envelope in various spots with something like a pencil. (Please feel free to cheerfully ignore those who admonish that you 'shouldn't' do this - it won't do any harm as long as you don't go crazy, and it is positively diagnostic, though it's true that a negative test result can't be taken to mean there still couldn't be problems). Any ringing or rattliing heard through the speakers means time to replace, and the louder and more lingering the audible results, the sooner the better. A good tube should display near silence when tapped. I recommend doing this test routinely every time you check the bias settings on the output tubes, since the problem can develop slowly and the deleterious effects are insidious but subtle at first. I would also do this test once a week for about 6 weeks after first installing a fresh pair, because you will want to replace new tubes under warranty if they show any incipient microphony during the break-in period. And although they're much less prone to developing an audible problem in this area, go ahead and do the same test on the driver tubes while you're at it, as they can occasionally become physically noisy too.

Along those same lines, I also recommend that anyone with these or similar amps make a small investment in some kind of resonance-damping rings for the input tubes, at least the inexpensive silicone types if not something more elaborate. They're cheap, they help, and many amp makers now install them as standard at the factory. Anything you can do to cut down on resonance in the input amplifier tubes will likely result in cleaner transient reproduction, more even frequency response with less tendency toward increasing brightness and forwardness under dynamic conditions, and more stable and coherent soundstaging and imaging with an overall greater sense of 'calm' and ease.