No love for the KT 90?

Ok returning back to the KT90EH...

I recieved them a few days ago. So far they have maybe 15 hours on them.

I would like to restate that i'm very new to the tube sound. So I hope this opinion will be useful to someone.

Current system is a rebuilt ST-70 using the VTA driver with 6SN7 tubes. Also i've opted for a new power tranny. Picture is the third down on http://www.tubes4hifi.com/ST70.htm main page thx Roy. I'm running all custom speakers and custom crossovers. Dayton Audio RS125-4 x 2 and Tang Band 28-847SD per cab. Listening source varies. Pro-ject turntable and digital sources.

Currently I have them biased to 50ma. I believe my bottle neck for power is the stock ST-70 OPT's. That being said the system provides plenty of power for my needs.

If you haven't seen a comparison check out the pic below. Although the tube glass is roughly the same size the tube elements are much larger. You can see the base is very low profile. I kinda wish it was a little more substantial. At first glance they are not as different looking to the old KT77's as a KT88 or fat glass tube would be. So.. they are larger but not as impressive looking than a KT88 would be I guess.  

At first power up I noticed the highs being a bit soft and the bass was over emphasized. I came across a post with a similar experience so I don't feel alone in this. They have leveled out but there are still very new. Right now they don't sound terrible. The bass is still a bit heavy but not all together unpleasant. Once I get more time on them I will try to give a more detailed impression. Right now i'm on the fence.    Just got the Gardians Of The Galaxy LP. Its not sounding to bad right now.  

These observations are in relation to the EL34 and KT77 tubes I was running previous. Also my complete lack of exposure to any other tube amplifiers. I preferred the sound of the KT77  over the 34's so the 34's were shelved quickly after I got them. I will have to try the 34's again to see if my opinion stands.




---KT77---

Thanks for the info an pic..................I to like the tone of 6SN7 inputs
i have had the EI KT90 for years....these EI are not made any more..the KT90 can take 7-800B+v on there plates....if there ran with 600v on the plates thay do open up an topend gets better....but i dont like the sound of any output tube ran with more 460-80....ran on there plates
But sound wize your right on....the top is not rolled off ......But it sounds to me like the mid is push out an the base sounds fat..some amp input tubes can match well....but the 6SN7 can sound dark with some tubes....KT90,KT88.....an maybe the KT120s-150s.........6550s an the 6SN7 is a sweet setup...an some of the topend i ever had.............
The top-end on the KT77,EL34 well be much more open...well to me
I have got great sound out of my Dynaco MK3 with the old stock 6AN8 inputs....
there top-end can sound brite...the KT90s sound right in this setup.....



Thanks for the site Bob........................

Good info ... nice to see a "real world" review. Also impressed with the EXACT matching based on the box stickers ...

Pushing the bass can be a good thing, and something I like about the KT120's. Long as the mid bass doesn't get muddy, I'm cool wit dat.

Pushing the mids is also a good thing IMHO, as that's where the ears typically begin to fail as we age, or at least fail in the spectrum that's most noticeable, as in vocals. I agree the B+ could be a factor as the tubes will never develop their full potential in the ST120. Then again, same could be said about the KT120's, although they perform extremely well in this application.

Fun research!

PS ... things that make you go "huh"? What's with all the blank posts? Some heavy handed modding going on in the background?

12AU7-12BH7.............Bouth being vary close to the Big boy the 6SN7...may give better top on the KT90-120...well i think thats your point about the 120s in your amps...sounding good to you..
I have B&Ws..Apogee speakers....that can get a hot on the topend...6SN7 an the KT88-90s can sound great.....
But get a littel dark on the ESLs.....Magnepans...this is where the 6550s come in...thay need the 6SN7 to give that richness but still...open up the top up....hehe...tubes in 2014 gofig



Thanks for the site Bob...................

zx wrote:12AU7-12BH7.............Both being vary close to the Big boy the 6SN7...may give better top on the KT90-120...well i think that's your point about the 120s in your amps...sounding good to you..

You may have run into a post of mine showing my driver collection ...



Fun rolling them in and out to suit the system. I do know that with both the Psvane KT88's and Tungsol KT120's, the top end was overly bright for my tastes. I tamed that down a LOT with a couple dampers at the primary reflection points on the ceiling AND using a sweet little triplet of Westinghouse "Star" 5963's. I also have the advantage of being able to roll tubes in my Maverick DAC to tailor the sound - that's now sporting a Tesla 6CC42 that was also quite bright with other drivers in the amp, but works real well with the current set. All working well enough that I haven't rolled a tube in several months now.

And ya ... the KT120's are exceptional in this amp, but ... long as I'm looking for another set, might as well see what's out there. Truth be told, I' kinda sorta leaning towards the Penta Labs KT88's at this point. People who got em seem to like em.

Penta Labs KT88's .....had 4ea here new...for two weeks...in a VTL amp i retube for a guy...
Look an sounded good....but not better than my standby sovtek,ys...$200.for KT88...not...
But hay thats me....
i may go for the KT120s.....but i know you have 120s....but i well get the golden gate KT88s..just for fun....i got a lot of tubes here....thay wont die....i run that 480B+...by the way what your heaters runing in you amps..........outputs tube can run a littel hot 6.5-7....but inputs should not be over 6. for the best sound ...if i run the above 6.2-3....that all seam to get briter....hhscott runs there input tube at 5.5-7 DC.....best sound ever....to me anyway


Thanks for the site Bob.....................

sKiZo wrote:Good info ... nice to see a "real world" review. Also impressed with the EXACT matching based on the box stickers ...

Just for everyone's info - those tubes will not match perfectly once installed as the components in the amp are not EXACTLY matched...

Once tubes are matched within a reasonable tolerance there is nothing else to be gained by getting a closer match in all but a VERY few cases. What is more important is how the matching was done:

1. Was the tube run-in for a significant length of time to minimize the amount of drift that occurs after the tube is placed in service?

2. Was the tube matched at voltages/currents like those the tube will see in real world service? And while it was good and hot?

3. Was the tube checked for excess screen current draw?

4. Since most gear requires measuring cathode current - not just screen current - to set bias, was the tube matched according to cathode current (not just plate current!)?

Those are FAR more important to the purchaser than "exact matching", especially if the exact matching was of the plate current only instead of cathode current.

Just a heads up ... I pulled the trigger on a factory matched set of TAD's.



Tube Amp Doctor KT88-STR Vacuum Tube

The latest version of our TAD KT88-STR is built in the style of the early British MOV KT88. It has the same big and heavy glass envelope and beautifully polished metal base. Its wonderful tone and great appearance make this tube the most attractive choice for high-end audio applications and powerful bass guitar amps.

It offers a vivid and three-dimensional tone, pleasingly warm, detailed and with subtle highs. A very musical reaction, with great sound and finest details in mids and top-end; a linear and harmonious overall response with a very natural tone, make the TAD KT88-STR our favorite tube in the KT88 and 6550A class.

I'll let you know how far I got my heads up my rear when I get them installed.  

sKiZo....
I would like to know your thinking on the diff in sound if any.....in the KT120s....an any other kt88 you may have....i dont use Chokes in my tube amps are preamps B+s any more.... i know you have a upgreaded one for two ch in your Amp....What is the B+ in your amp befor an after the choke??......
thanks for any an all input on the sound...





Thanks for the site Bob............Miss Bob.... is he bizzy or just haveing fun??

Jim McShane wrote:

sKiZo wrote:Good info ... nice to see a "real world" review. Also impressed with the EXACT matching based on the box stickers ...

Just for everyone's info - those tubes will not match perfectly once installed as the components in the amp are not EXACTLY matched...

Once tubes are matched within a reasonable tolerance there is nothing else to be gained by getting a closer match in all but a VERY few cases. What is more important is how the matching was done:

1. Was the tube run-in for a significant length of time to minimize the amount of drift that occurs after the tube is placed in service?

2. Was the tube matched at voltages/currents like those the tube will see in real world service? And while it was good and hot?

3. Was the tube checked for excess screen current draw?

4. Since most gear requires measuring cathode current - not just screen current - to set bias, was the tube matched according to cathode current (not just plate current!)?

Those are FAR more important to the purchaser than "exact matching", especially if the exact matching was of the plate current only instead of cathode current.

Hey Jim, in my experience, a lot of tube sellers are not using the right equipment for testing and are essentially selling random tubes.  

I see on your website...

When we match tubes, we are most interested in how the tube "idles" or draws current.

You cannot effectively match power tubes on a typical tube tester. Tube testers never applied the amount of voltage necessary to get accurate measurements of power tubes. In fact, there are only a couple very rare models that will allow you to get close to the voltages needed and allow you to read the parameters correctly. We use custom-built testing equipment that is the best in the business. We burn in and test power tubes at real voltages, and we test them for shorts, grid leakage, and excessive current draw before and after burn in to help minimize the chances of using your amp as a tube tester.

I did buy a set of Tung Sol 6550s from you and they've been fantastic sounding.  

Are you familiar with Roger Modjeski's RAM Labs tubes and his testing / selection techniques?  Here's what he writes about the subject...

My experience gained from testing thousands of EL-34's, 6550's, KT-88's, and other tubes has produced a wide bell curve of the two most important parameters, Bias and Transconductance. The center of this curve is the "bogey" value that the manufacturer is trying to hit, and the ends show the cutoff points of what he is willing to allow out of the factory. The tubes at the ends are still perfectly functional, but may not work well in all amplifiers, and will certainly not work well if mated with another from the opposite end of the curve.

Some amplifiers do not have enough range on the bias pots to handle the range of tubes so that selection-must be made from a particular part of the curve to ever achieve bias.

In the "good old days," I'm told, the spread of values was much less, allowing reasonable performance with random selection. Today, random selection is strongly not recommended

(Edited for misquote correction)

corndog71 wrote:

Jim McShane wrote:

sKiZo wrote:Good info ... nice to see a "real world" review. Also impressed with the EXACT matching based on the box stickers ...

Just for everyone's info - those tubes will not match perfectly once installed as the components in the amp are not EXACTLY matched...

Once tubes are matched within a reasonable tolerance there is nothing else to be gained by getting a closer match in all but a VERY few cases. What is more important is how the matching was done:

1. Was the tube run-in for a significant length of time to minimize the amount of drift that occurs after the tube is placed in service?

2. Was the tube matched at voltages/currents like those the tube will see in real world service? And while it was good and hot?

3. Was the tube checked for excess screen current draw?

4. Since most gear requires measuring cathode current - not just screen current - to set bias, was the tube matched according to cathode current (not just plate current!)?

Those are FAR more important to the purchaser than "exact matching", especially if the exact matching was of the plate current only instead of cathode current.

Hey Jim, in my experience, a lot of tube sellers are not using the right equipment for testing and are essentially selling random tubes.  

I see on your sight...

When we match tubes, we are most interested in how the tube "idles" or draws current.

You cannot effectively match power tubes on a typical tube tester. Tube testers never applied the amount of voltage necessary to get accurate measurements of power tubes. In fact, there are only a couple very rare models that will allow you to get close to the voltages needed and allow you to read the parameters correctly. We use custom-built testing equipment that is the best in the business. We burn in and test power tubes at real voltages, and we test them for shorts, grid leakage, and excessive current draw before and after burn in to help minimize the chances of using your amp as a tube tester.

I did buy a set of Tung Sol 6550s from you and they've been fantastic sounding.  

Are you familiar with Roger Modjeski's RAM Labs tubes and his testing / selection techniques?  Here's what he writes about the subject...

My experience gained from testing thousands of EL-34's, 6550's, KT-88's, and other tubes has produced a wide bell curve of the two most important parameters, Bias and Transconductance. The center of this curve is the "bogey" value that the manufacturer is trying to hit, and the ends show the cutoff points of what he is willing to allow out of the factory. The tubes at the ends are still perfectly functional, but may not work well in all amplifiers, and will certainly not work well if mated with another from the opposite end of the curve.

Some amplifiers do not have enough range on the bias pots to handle the range of tubes so that selection-must be made from a particular part of the curve to ever achieve bias.

In the "good old days," I'm told, the spread of values was much less, allowing reasonable performance with random selection. Today, random selection is strongly not recommended

Corndog, I sent two octets of randomly bought NOS original TS 6550s to tubes4hifi bought locally and off fleabay and audiogoner for testing plus a couple of used ones. He stuck them in a MK-III he was building and all came within ~5% of each other on bias @ 425 VDC, according to Roy. He tried one pair at 460V and bias remained steady. So yeah, you're right, the oldies are the goodies.

Very large trust factor involved in tube testing ... trusting that it's done right, and just as important, consistently. And agreed, you're in the bonus round if your amp can be tweaked for each tube once installed.

What's interesting on the TAD tubes is that they're available from another source with cryogenic treatment at about the same price the factory outlet sells them for. Difference being ... even if they start with a factory matched set, what effect does the cryo have on the tube's characteristics? They do tend to go on about how much more musical the tubes are after treatment, but one thing that came up in conversation is that the Gm at least changes significantly. No specifics on other electronic changes. I figured in this case, factory knows best, and TAD does have a rep of tight QC with their products.

And yes ... I'll be sure to post back with my impressions compared to the KT120's. In fact, I'll go give those a listen now just for practice. Picked up on a copy of the original Mercury Box Set and plan to work my way through that - I figure that should burn in the new tubes nicely.

And speaking of testing, just made a new addition to the library that should put it through it's paces ... I'll let yall know when I finish with it ...

corndog71 wrote:Hey Jim, in my experience, a lot of tube sellers are not using the right equipment for testing and are essentially selling random tubes.  

I see on your website...

When we match tubes, we are most interested in how the tube "idles" or draws current.

You cannot effectively match power tubes on a typical tube tester. Tube testers never applied the amount of voltage necessary to get accurate measurements of power tubes. In fact, there are only a couple very rare models that will allow you to get close to the voltages needed and allow you to read the parameters correctly. We use custom-built testing equipment that is the best in the business. We burn in and test power tubes at real voltages, and we test them for shorts, grid leakage, and excessive current draw before and after burn in to help minimize the chances of using your amp as a tube tester.

I did buy a set of Tung Sol 6550s from you and they've been fantastic sounding.  

Are you familiar with Roger Modjeski's RAM Labs tubes and his testing / selection techniques?  Here's what he writes about the subject...

My experience gained from testing thousands of EL-34's, 6550's, KT-88's, and other tubes has produced a wide bell curve of the two most important parameters, Bias and Transconductance. The center of this curve is the "bogey" value that the manufacturer is trying to hit, and the ends show the cutoff points of what he is willing to allow out of the factory. The tubes at the ends are still perfectly functional, but may not work well in all amplifiers, and will certainly not work well if mated with another from the opposite end of the curve.

Some amplifiers do not have enough range on the bias pots to handle the range of tubes so that selection-must be made from a particular part of the curve to ever achieve bias.

In the "good old days," I'm told, the spread of values was much less, allowing reasonable performance with random selection. Today, random selection is strongly not recommended

Actually, the excerpt you posted is not from my site. It is a pretty good passage though, and seems to indicate some genuine care is used by that vendor to test the tubes he/she sells.

I am familiar with Roger's operation to an extent. I don't agree 100% with his description of the "spread" though -in many cases I find the new production tubes to be actually a bit closer than the old stock. But it really is a moot point anyway. If you need properly matched tubes for your amp you can't count on most of the common tube testers to do the job. And for power tube matching some custom built test gear is pretty much a necessity to get accurate matching. My AT-1000 Amplitrex will deliver up to 500 volts at a decent current, but my "McShane" rig can go even higher voltage and much more current.

And finally I'm very glad you are enjoying the 6500s!

Jim McShane wrote:Actually, the excerpt you posted is not from my site.

I am so sorry! I don't know how I got you mixed up with Upscale Audio. My mistake.


I don't believe Roger said anything bad about new tubes except that consistancy can vary which is all the more reason to get properly tested tubes. I think "tested" is the word I should've used before vs matching.

Anyway, I apreciate your comments.

Excerpts from the TAD catalog (page three)...


Tubes must be properly burned-in to provide the stable and reliable
data that is required for quality tube matching.
This is a time- and energy-consuming and cost-intensive process,
which most new tubes on the market are not subjected to. During
the extensive TAD burn-in procedure, the tube’s cathode surface
is formatted, which balances the tube’s emission and offers increased
dynamic headroom. This in itself leads to a better overall
response and smooth tone. TAD Tubes offer maximum reliability,
consistency and sturdiness for one goal: the ultimate tone!

Before a TAD Tube receives our seal of approval, we perform extensive sample
evaluation testing: consistency, power, and shock resistance are tested, we
perform a “soak test” (long term operation at full power) and, of course, a
“sound and music” test with the tubes operating in amplifiers we know, so we
can learn about the sound character of our tubes and how they perform in different
musical styles and different amplifiers. The main tests are conducted after
a proper pre-aging - to stabilize the cathode emission - has taken place. While
most tube test equipment does work at a maximum 250V, we built our test rig
to operate at voltages of 360 to 600V, depending on the tubes that are tested.
Every TAD Tube is tested by our qualified staff. Each pentode is inspected and
tapped during operation – we listen for noise floor, hum and “odd noise.” Finally,
we measure the tubes according to a pre-defined set of parameters and
match them by Ia (PC) and Gm (TC). We test batches of 400 to 500 pieces per
run to ensure tightest tolerances of typically 0.5mA for PC-levels.
All TAD Tubes and boxes are labelled with the PC and TC test results and a
unique serial number, which allows us to identify every tube we have ever
tested. We permanently verify and monitor selected and matched TAD Tubes
by using them every day in our own amp service department and in the TAD
Amp Kits we assemble.
This is the most complete quality control system we can imagine. All done inhouse
at TAD in Germany.

http://www.tubeampdoctor.com/pdf/TAD-Products_Info.pdf

As mentioned, I did have concerns (still to be addressed) as to what effect a cryo process applied after the fact would have on the tested parameters (which to me seem pretty much inclusive).

PS ... this has been fun. I should oughta buy more tubes. Can never have enough tubes. Definitely. Tubes!

I believe that most vendors will cyro-treat a large batch of tubes. And after the treatment, will re-test each tube and reassemble them into matched pairs/quads.

Q: How many tubes are enough?
A: One more than you already have.

skriefal wrote:I believe that most vendors will cyro-treat a large batch of tubes. And after the treatment, will re-test each tube and reassemble them into matched pairs/quads.

Which closes the circle ...

My concern with cryo is that the process DOES apparently change the electronic characteristics of the tube, so that leaves us with the question as to whether the "improvement" is actually an improvement over the original factory matching. A lot would depend on how inclusive the post-cryo testing is.

deepee99 wrote:Q: How many tubes are enough?

You're saying I should just get a set of each to put the question to rest?
(Way to enable my addiction, you dirty rat, you ...)

You're saying I should just get a set of each to put the question to rest?
(Way to enable my addiction, you dirty rat, you ...)

Well i do have more than one tube Amp...............more like 8 to day...........But the more tubes the better...
If you keep the B+....at 480V.....i have not lost an tubes in years.........thay i did not DroP..
Hehe....It happen.....but in my MK3s i have ran one ea KT90 an one KT88 an got great sound!
An even with one amp......most people cant just chang the outputs AMps... Tube amps 2014....Heh

Have fun your only here for a Min......



Thanks for the site Bob........




.





.

I'd like to hear Jim McShane weigh on the cryo business. Opinions range from that it's the greatest thing since sliced bread to that it's snake oil. It would be nice to hear from somebody who knows what he's talking about.

one thing I noticed when I got cryo KT120's for one of my clients amps was that they looked 'aged' on the inside. All the plates were kind of pitted and I also saw some silver flakes inside all of them, like it came from the getter.
Sound wise, for the short period I had them running, I could not hear any differences between those and non cryo'ed KT120's.

Ok, I've been reading this thread with interest but with a little skepticism. I'm certainly a tube noob and I am assuming that the original tubes in my dad's ST70 are going to have to be replaced (once I finish the rebuild). So my question is this: all other things being equal, what makes one tube sound different from another? coatings? physical spacing? differences in ear drums? or the ever present risk of "I paid more for these tubes so they MUST sound better"! Also (since the last time I heard this amp play I was a kid) what modern tube represents a good VALUE and sounds as close to the original tubes as possible? I want my dad's amp to be the baseline sound so I have a point of comparison if/when I build a new kit amp with all of the possible upgrades. BTW I hope my choice of using an 80/40/30/20 quad cap won't alter the original sound too much as I'm trying to keep this amp's signal path as close to original as possible.

n3ikq wrote:Ok, I've been reading this thread with interest but with a little skepticism. I'm certainly a tube noob and I am assuming that the original tubes in my dad's ST70 are going to have to be replaced (once I finish the rebuild). So my question is this: all other things being equal, what makes one tube sound different from another? coatings? physical spacing? differences in ear drums? or the ever present risk of "I paid more for these tubes so they MUST sound better"! Also (since the last time I heard this amp play I was a kid) what modern tube represents a good VALUE and sounds as close to the original tubes as possible? I want my dad's amp to be the baseline sound so I have a point of comparison if/when I build a new kit amp with all of the possible upgrades. BTW I hope my choice of using an 80/40/30/20 quad cap won't alter the original sound too much as I'm trying to keep this amp's signal path as close to original as possible.

sound is EXTREMELY subjective as you may well imagine.
But yes, different model power tube do sound different, no doubt about that. To my ears, Kt88' as well as KT120's have more bass and seem to be able to handle a wider frequency range than say EL34's.
For driver tubes, I prefer the sound of 5963's instead of a lot of 12AU7's as driver tubes, I also like the sound of the 6SN7's and 6SL7's as driver tubes, I use those in the ST120's and M125's.

I am assuming your ST70 has the older smaller power transformer, as I would suggest trying the KT88's, but the smaller transformer will REALLY struggle with those, not really helping in the overall sound, so you would not get the full benefit of using KT88's in your ST70.

Keeping things original can be good and/or bad. In case of an old tube amp, I would upgrade as much as I can, the difference in sound is SO much better and will astound you!

Not all tubes of the same type are created equal. Heavier structure, modified elements, assembly details, metal alloys and even the glass used, can have major effects on the end product ... no shortcuts to quality here.

I did get the TADs in yesterday's mail. First thing I noticed is they are HEAVY compared to my Psvane KT88's. Those are also rated quite high, so that should give some indication as to the quality of the TADs. Plugged them in - biased right up, and stayed steady after idling for several minutes. Fired up the system and played a rather eclectic selection I like to use for testing purposes and they really held their own against what I'm used to hearing out of the KT120's. Strong bass was always a major factor in what I liked about those. The TADs are easily as strong on the bottom, and have greater definition and impact. We're talking some serious PUNCH here. Vocals and mids are pleasant, and the top is all there.

*No changes other than the bias, which I set to 55mV vice the 60mV used with the KT120's.

Keep in mind we're talking fresh out of the box here ... I expect some improvement over time, but truth be told, won't be seriously disappointed if they stay just as they are.

If I had a complaint (and I do so love to complain), I noticed the top spreader that centers the internal structure in the glass is slightly off center on one of the tubes. I might have to get all anal retentive about that and request an exchange. Or not. Doesn't seem to make any difference in what I'm hearing ...

Oh ... and the boxes are overlarge - I imagine to fit their tallest tubes. Not an issue except that the tubes had a good inch of headroom to slide back and forth inside during shipping. I DID drop a note to TAD about that ... either a plastic peanut or a wad of bubbles could prevent that easily. They did triple box the shipment ... no complaints there.

In the 90s...i had a Jadis Defy7.....I got 15 KT100s the Defy needed 12 tubes an came stock with GE 6550s
An then maybe 2004-6 i got the  EI KT90s...the sound of the KT100-KT90s Had a littel stronger uper mid an diff bass than the KT88s.........What you say about the new Kt88 an the KT120 sound is about right...in the end the KT88 for me... takes the day for power an tone....in my amps the 6550 can be vary sweet......it all about the uper mid an top end with 6550s....the KT88 can sound like a Big 6550 with more power an big bass...THE KT90-100-an maybe the KT120-50...amps may need to be setup a littel diff....in time well see.....but in the tube amp i have the the biger tubes are Darker sounding......................well to me...i have not got into the KT120s...Golden Gate 88 just look fun....
Thanks for any an all info pic....of tubes....


Thanks for the site Bob.....