Retubing an ARC VT100 mkll

Thinking of tube rolling my VT100 mkll. Currently using EH for both the 6922 input and 6550 output tubes. Less than 800 hours on the entire set, so its not that I need an entire retube, just looking to improve the sound if possible. What would give the biggest improvement, changing out the input or output tubes to KT88/90? Bear in mind I would need a closely matched OCTECT of either so bizarre/rare vintage tubes are out of the question. Thinking of Gold Lions or similar, any thoughts from the scholars?
Gold Lion or Shangwaung Treasure KT-88's are both excellent
I have a Cary SLI-80F1 integrated with Genelex KT-88's and like them very much. As for the 6922 varients I use Amperex 7308's from Upscale Audio and again really like these tubes. I know you said no NOS tubes but these were a vast improvement over the EH 6922 tubes. For current production tubes you may want to try the Genelex here as well but they are kind of costly IMO and I have never tried them so I can't comment on how they sound in my amp. Otherwise for reasonably priced current production tubes I have had good luck with the EH tubes.
I believe there have been a few issues with the 6550EH's and ARC gear. They are currently using the Sovtek 6550WE. I would continue to use the 6922EH as that is the tube that product was voiced with.
Thanks to all. Guess the 6922EH's stay, and an octect of GL KT-88's are on the upgrade menu.
Hifigeek (Gary), will the VT 100 MkII take the KT120. I found the KT120 to be substantially superior to the 6550.
Bifwynne, I have to find my thread or the list of ARC products that can use it. I think there is an issue with space in the VT100 series. The KT-120 is too tall I believe.....
From what I can see, there should be oodles of room to physical fit KT-120's. Not sure if the bias range or power supply can support this tube though. Anyone know for sure as I have also heard good things about this tube, but have not investigated it as I did not think it was compatible. Anyone know for sure?
I don't know if this list has changed but here are the ARC amps that Hifigeek1 mentioned in a different Tung Sol KT-120 thread.

04-19-12: Hifigeek1

The following is a list of ARC amps that are authorized to use the KT-120:

VS55, VSi55, VS60, VSi60, VS110, VS115, REF110, VM220.

I hope people find this useful as there seems to be a lot of confusion about it.
Thank you Jedi. May the force be with you always!
I retubed my VT100 MKII with the KT120s without any issues. The improvement in sound and perfromance was across the board in all sonic categories. In fact the amp seems to run cooler with these tubes.
The filament supply was not designed for the extra current needed to run the KT-120. The above list is from Audio Research and represents what they have tested and are comfortable with running KT-120's in. Caveat Emptor.
My dealer Lyric told me the opposite. The VT100 MKII was on the list of approved amps for the KT120 upgrade. I was called specifically by the rep and given this info because I had enquired previously about using the KT120s.

Did you get the list from ARC or is your comment based on second hand info?
I received the list from ARC as I am a warranty repair station for them. I suggest you contact ARC and speak to Kalvin. I suppose it's possible they updated the list. But that's news to me.
Just waiting for the first report of someone popping the filament winding.
It's bound to happen at some point.
I spoke also to ARC. No problems were anticipated. The new bulletin about compatibility from ARC was issued in the Feb/March 2012 period.
Awesome. Well they don't keep me in the loop. So the issue isn't whether the amp can handle the increased heater current because it can, the issue is the fact that the tubes are mounted horizontally. Because the KT-120 is longer and heavier, there is a risk of tube sockets loosening up to the point where the tube looses contact with the socket and the tube arcs. That is basically the issue. That is why ARC does not support the use of KT-120's in that amp. BTW it does sound very good with KT-120's. now I'm torn between the KT88 Gold Lions or, for similar money, the Tung-sol KT120. Hifigeek1, if you were going this route, which would you likely go with? Thanks!
Well I'm not a fan of KT-88's in any ARC amp. I would make sure the output tube sockets were nice and tight and go with the KT-120's. Just so you know you can't just put any 6922's in that amp. I get them from ARC and it requires a 1-2 hour set up procedure so that distortion is low and the DC balance is correct.
Go with the KT120s you wont regret it. They will make a substantial improvement in your VT100MKII.
There are no issues re loose sockets, etc, as Hifigeek suggested.

I may not be a service rep, but I am very cautious and made sure that I investigated negative possibilities before making the change to the KT120s.
Thanks to all for your assistance on this. I plan on keeping the EH 6922 signal tubes, I just got through re-biasing them at about their midlife (using the A. Collins method). And my current output tubes seem to fit very snug, so I think a couple of quads of KT120's are on now on the menu. Will let everyone know how it goes. Cheers!
Call ARC and buy a set of their new 6550s. I replaced the power tubes in my REF-PH8 and my REF-3 with these tubes. At first listen, there was a blacker background with much better definition and separation. Once broken in ... amazing.
OregonPapa, you mean you can hear a big difference after you replace that regulator pass element 6550 in the PH8 and Ref 3 Preamp? How old was the 6550 that was replaced?
The REF3 and PH8 both use a 6550C for power supply regulation.

Are you suggesting that based on these data points, Sinaker01 should use the 6550C instead of the KT120 as power tubes? Perhaps you haven’t noticed, but ARC has replaced the 6550C power tubes with KT120s in all of its current amplifiers.
BTW Never use a KT-120 for the regulator pass element in any ARC product. It's a definite no no.
Ok, so, just finished installing and biasing (adjusted to the same 130 mV the amp recommends)a matched octect of Tung-Sol KT120's. Less than an hour playing time skipping through a bunch of artists I am familiar with(now Keith Jarrett playing J.S. Bach) and the verdict is positive so far. Can't speak to whether it can play louder than the EH6550's but they sound very good-perhaps a touch more effortless and glassy than the Electro Harmonix tubes but that could be just fresher tubes, hard to say. Mind you, the 6550 were only put in last Fall, so they were probably just at their "half life" based on my listening habits. Will keep the group informed as they break in, but good news is nothing went bang and they are dead quiet as well.
So the verdict after decent breakin time- they're pretty good. Not what I would call a flat out night and day difference but a bit more "drive" and a little less glare in the upper ranges especially when the volume is turned up. All in all I'm pleased for the $450 spent, but I will give full props to the EH6550 tubes - they were a good value. Assuming I can get 2 years out of the KT120 set, I am happy with the change over. BTW, one big physical difference is the heft and weight of the 120 vs the 6550. These things feel like they're built to last. Cheers!
Just a footnote comment about the KT-120s. I had about 3000 hours on my KT-120s and thought it might be a good idea to retube my amp. I bought a complete set of tubes from Upscale Audio and dropped them in. The price is about half what ARC would charge. Kevin Deal burns in his tubes for 72 hours before matching and then checks three electronic attribtes: bias, G2 and transconductance. After about 20 hours of break-in, it's quite obvious that the amp sounds better. FWIW.

Btw, one of the matched sets did not take a bias adjustment. I put an old tube back in and everything was ok. Called Kevin. He immediately shipped out a replacement matched tube. Everything is now good to go!!
Wow 3000 hrs. is well passed the recommended ARC replacement time. I would say you got lucky..
Gary, I'm sure you're right. But I wonder if the KT-120s are as susceptible to arcing or other malfunctions that would damage the amp as compared to the 6550 C tubes. The build quality impresses me that the KT-120 may have a longer life than 2000 hours.
I can tell you, they're still susceptible. If your amp was wired in triode, you might be able to get away with it.

Is the ARC VS 115 wired in triode?? Regardless, thanks for the advice anyway. The 6H30 audio tubes were pushing between 4 and 5K hours too. So I retubed the whole VS 115 batch.

As an aside, I just ordered a retube set FROM ARC for my ARC Ref 5. There's probably over 3K hours on the 6550 C and 4 to 5K hours on the 6H30s.

Not sure what I did makes sense, i.e., buying VS 115 tubes from Upscale Audio and Ref 5 tubes from ARC. The thought process is that "ARC grade" matching might be more critical in the line stage than the amp. That's probably not a valid assumption, but it's a done deal. In any case, as stated, the KT-120s bias just fine and the amp sounds great, so I'll just have to "suffer" [sic] with the Upscale Audio tubes in the amp -- NOT.
Next time let me know BEFORE you buy your tubes. I can help.
No way the vs115 is triode. 4 tubes push pull per ch will not get you 110wpc even if you push B+ all the way to 550v.
Thanks Gary -- will do.

Gary and Johnsonwu -- I'll probably regret this question, but what is the significance of a triode amp? Btw, with KT-120 tubes, the VS-115 can push out 130 wpc, but my ears would bleed if I pushed my amp and speakers that hard.

Thanks again,

Triode-wired tubes give a more refined sound. Richer in inner detail as many would call it. I would describe the sound as more linear, the microdynamics of low level passages are better preserved so you wont spent time hunting for the right listening volume.

In pentode or likely Ultra linear in the VS115 config, you get better bang for the buck esp in the dept of bass dynamics. if you like gut punching bass, keep it as it is. If you love violins, female vocals, and choral music, AND your speakers are 89dB/W/m or better, go triode.

Triode-wired tetrode or pentode tubes can last longer assuming same B+ and bias in both modes.

Many amps can be rewired to run the power tubes in triode mode. Pull the screen grid input resistor and connect the screen grid to the plate via a 100Ohm flameproof resistor. But it really depends on whether the biasing circuit has enough range to get the tubes biased to the 55-65mA per spec after triode conversion.
You also lose about 30% of your total power output. Clipping is much softer.