6550 or KT88 for a VTL MB450

jazzdude99

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Jul 11, 2021
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Hi All

looking for a new tube set for my VTL MB450 series 1 amps. Can you give me a compare and contrast in sound quality between the 6550 and KT88 please?

I know this is a pretty generic question with lots of variables, but what are the big ticket differences between the two tube types? I’m currently using 6550 - I have an aging set of winged C and new issue Tung Sol.

cheers

Andy
 

TheMooN

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Jul 30, 2013
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If you wish to stick with 6550’s I would recommend circa 1970’s production General Electric 6550A JAN. .
 

jazzdude99

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Jul 11, 2021
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Thanks chaps - in terms of actual tube recommendations, I need to be practical. I need 16 tubes for these amps, so NOS would be very challenging. Likely limited to new production - VTL themselves recommend the Gold Lion KT88 reissue, My question was what changes would I expect between 6550 and KT88.

thanks
Andy
 

Fedie

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Jan 19, 2020
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I have MB 250 mono blocks I use tungsol 6550 never tried Kt88 the 6550 have been very reliable had 1 go bad in the last 5 years..
 
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marty

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Apr 20, 2010
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I think your tube complement is going to be very similar to the Siegfrieds which I owned for several years. The first decision you need to make is to decide whether you want to run in pentode mode or triode mode. This may depend on the efficiency of your speakers and loudness requirements. This may also govern tube preference. 6550s are a bigger brute force tube whereas the KT88 are more musical and refined. The GE 6550s are excellent as mentioned. However I preferred the KT88's by far but I also ran my amps in triode mode so it was a good synergy. As far as brands, I used the Gold Lions and they are very good. But I subsequently changed and bought several sets of KT-88s from Kevin Hayes at VAC who sourced them from Shuguang. They make a particular tube model , KT88-98 that is readily available and affordable from many vendors which I then used as my regular tube. (Kevin charged a small premium for his quality control and "VAC" labeling, but a good vendor can do the same matching and QC on standard KT88-98's which was Kevin's preferred tube at the time). I switched from the Gold Lions to the Shuguangs not so much for SQ (both are excellent) but longevity and reliability (Shuggies were a bit better). You should expect 2000 hours of life for a good KT88; 2500 if you're fortunate. As with all tubes, there is no "best" as personal preference is, well, personal. But the Shuguangs and Gold Lions are both sonically excellent. I have not tried the newer "premium" versions of the Shuguangs (i.e. Treasure series) so there's that to consider as well. No idea if these have improved SQ or lifespan or both. But if Kevin Hayes at VAC has gone that route, that would be good to know. You should also ask Bea Lam, who has some of the best ears in the business. Her opinion would be worth learning.
 
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jazzdude99

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Jul 11, 2021
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Thanks for the great information Marty - very helpful.

I did contact Bea Lam - they are recommending the Gold Lion KT88 reissue.

you’ve given me some food for thought!

Many thanks

Andy
 
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microstrip

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May 30, 2010
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I think your tube complement is going to be very similar to the Siegfrieds which I owned for several years. The first decision you need to make is to decide whether you want to run in pentode mode or triode mode. This may depend on the efficiency of your speakers and loudness requirements. This may also govern tube preference. 6550s are a bigger brute force tube whereas the KT88 are more musical and refined. The GE 6550s are excellent as mentioned. However I preferred the KT88's by far but I also ran my amps in triode mode so it was a good synergy. As far as brands, I used the Gold Lions and they are very good. But I subsequently changed and bought several sets of KT-88s from Kevin Hayes at VAC who sourced them from Shuguang. They make a particular tube model , KT88-98 that is readily available and affordable from many vendors which I then used as my regular tube. (Kevin charged a small premium for his quality control and "VAC" labeling, but a good vendor can do the same matching and QC on standard KT88-98's which was Kevin's preferred tube at the time). I switched from the Gold Lions to the Shuguangs not so much for SQ (both are excellent) but longevity and reliability (Shuggies were a bit better). You should expect 2000 hours of life for a good KT88; 2500 if you're fortunate. As with all tubes, there is no "best" as personal preference is, well, personal. But the Shuguangs and Gold Lions are both sonically excellent. I have not tried the newer "premium" versions of the Shuguangs (i.e. Treasure series) so there's that to consider as well. No idea if these have improved SQ or lifespan or both. But if Kevin Hayes at VAC has gone that route, that would be good to know. You should also ask Bea Lam, who has some of the best ears in the business. Her opinion would be worth learning.

All good points, but we should remember that IMHO usually Shunguang tubes need a quality control that most vendors will not carry. Considering tubes, reliability depends a lot where we source them. Most of the times that people report problems with tube equipment is due to poor quality tubes.
 
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ca1ore

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Aug 31, 2010
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May be a moot point for a while as Russian new production tubes are essentially unobtainum at the moment. FWIW, I ran the winged C 6550 in my MB450s for a long time, then switched to the Gold Lion KT88s. Don’t frankly recall much difference. I’ve a set of new production Tung-Sol 6550 that I just bought in anticipation of supply problems. Still have life left on the KT88s, but these will be next up.
 
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Dentdog

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Jan 5, 2014
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Have run 6550/Kt88 in every amp forever. Have 10 or so brands, NOS/new issue you name it.
KR KT88s fill the bill. Don't want to be wordy here, don't need to. Best resolution and balance, very convincing.
 

jazzdude99

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Jul 11, 2021
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Thx for the recommendation - I need 8/ channel so a little spendy - will see where tube prices end up in a few months may become…..
 

Dentdog

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Jan 5, 2014
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Atlanta
I feel you, the Audiopax M100s in my system use 6 per channel. I have 12 tubes by 4 different manufacturers. Then considered the investment in my system overall and bit the bullet. Next best has been Sophia KT88. Psvane-good bass not as resolving. The step up in resoluton with the KR was worth it. Timbre is more charming as well.
 

jazzdude99

Member
Jul 11, 2021
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I feel you, the Audiopax M100s in my system use 6 per channel. I have 12 tubes by 4 different manufacturers. Then considered the investment in my system overall and bit the bullet. Next best has been Sophia KT88. Psvane-good bass not as resolving. The step up in resoluton with the KR was worth it. Timbre is more charming as well.
Excellent info - thank you!
 

WLGMuzza

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Oct 21, 2019
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I have a VTL S400 v1. I replaced the VTL issued 6550 tubes with tested Preferred Series KT88s from The Tube Depot. I had 5x failures before 1000 hours, and the green tube fault indicator on the front display couldn't be cleared, but otherwise the amp worked well.

I was convinced this was an issue with the amplifier logic, however VTL wouldn't consider looking at any potential problems unless I re-tubed with their factory tested versions.

I invested in a set of VTL issued GL at over twice the cost. Haven't had a problem since.

YMMV.

Good luck!
 

jazzdude99

Member
Jul 11, 2021
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I have a VTL S400 v1. I replaced the VTL issued 6550 tubes with tested Preferred Series KT88s from The Tube Depot. I had 5x failures before 1000 hours, and the green tube fault indicator on the front display couldn't be cleared, but otherwise the amp worked well.

I was convinced this was an issue with the amplifier logic, however VTL wouldn't consider looking at any potential problems unless I re-tubed with their factory tested versions.

I invested in a set of VTL issued GL at over twice the cost. Haven't had a problem since.

YMMV.

Good luck!
Thanks for sharing - I’ve used the Winged C 6550 that came with my amps when I bought them second hand, also reissue tung sol. I’ve had failures with both types, but they have plenty of miles on them.

I did speak with VTL about retubing, however they wanted me to send the amps in for that, which isn’t worth it. If they become available again, I’ll probably try the gold Lion Kt88.

cheers
 

EiK

Member
Jan 22, 2021
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I have an S-400. I followed the advice from Bea Lam of VTL, and bought KT88 from Gold Lion. Good sounding tubes, and better than the orginal 6550. More musical and better midrange. I had some issues with Gold Lion,and had a lot of failures. I therefore tried out Psvane KT88, and received confirmation that the tube where properly matched and measured. So, I have noe failures and I think they also better the sound (vs. Gold Lion). I can therefore recommend this tube.
 
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Sablon Audio

Industry Expert, VIP Donor
May 22, 2015
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Thx for the recommendation - I need 8/ channel so a little spendy - will see where tube prices end up in a few months may become…..
A trick to consider is mixing different brands / qualities of the same tube model. I once had a cj pr140 and found that using a single nos 6500 solid black plate tungsol in each channel mixed with 3 orginal Sovteks gave a fair taste of the legendary TS 6550 flavour.
 
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