No love for the KT 90?

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........




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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.....

sKiZo wrote: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.

So, what's the latest impressions on the TADs?

sKiZo wrote:I'd forgotten about the Golden Gate KT88 Super Tube.



Posted up about those a couple years back over on AK and only thing I got back was
.
.
.

(yup ... pretty much nothing)

They've been around for a while, and GuiGuang gets real decent reviews for sound quality and durability. And, like ... they're super! You'd think there'd be more folk using them at $100 a quad?

Have to keep them in mind as another option.

You can get them for $90.72 a quad and FREE shipping! https://www.tubesandmore.com/products/T-KT88-GG

poconoman wrote:

So, what's the latest impressions on the TADs?

Impressions? Well ... I scratched my name into them ... not!

Probably about a hundred hours on them now, and they're still holding their own against the KT120's I've been used to. Definitely tightened up across the spectrum for better detail.

Problem being - I'm a habitual tube roller and always looking for better. Since installing the TADs, I've also changed rectifiers (GZ37, but the NATO version) and drivers. Tried a few combos on those, and am currently using a Tele 12AU7 in the center and Westinghouse Star 5363's in the sides. My house voltage is also down from what it was so I've taken the bucker out of line.

So, are the improvements all TAD? Who knows" But I LIKE it!

---

Speaking of Golden Gate ... did some digging and found out they're made by Guiguang in China. Which apparently was bought out by Psvane a few years back. Fun fact ... the name literally means "light bulbs from GuangXi province". Apparently, the road's been rocky for them and ya takes your chances - which could explain the price. Also possible that the tubes are actually the best ever made and will make your farts sound like a symphony, but ... just sayin', as they say.

Here's an interesting (but dated) write up.
http://psvanetube.com/wordpress/who-was-guiguang/

Still might be interesting to pick up a set for an audition. Seems to me Tubes & More has a real decent return policy.

Interesting discussion on the development of the Kt-90 here:http://www.diyaudio.com/forums/tubes-valves/24313-electro-harmonix-kt90.html

Specs for the EI Kt-90 here:http://www.eierc.com/rc/KT90.htm

I know I like mine, powerful clean bass, lucid mids, sweet highs.

Great link! I'm on page three and had to stop to clean the blood off the monitor ... getting kinda heated!

One interesting tidbit I found ...

Recommendations for running the KT88 in an o/p stage are that the anodes be orientated 90° from each other and tubes be 4” apart on the horiz. The GEC spec stipulates that the envelope temperature not exceed 250°C.

Often wondered why push/pull sockets are mirrored ...

"Recommendations for running the KT88 in an o/p stage are that the anodes be orientated 90° from each other and tubes be 4” apart on the horiz. The GEC spec stipulates that the envelope temperature not exceed 250°C."

Looks like someone didn't get the memo:
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