KR and AVVT Tubes: Expensive Junk or Bad Luck?
JHPage
I'm curious if anyone has had any experience with KR or AVVT tubes, I
have bought 4 pairs of various types and have had problems with all of
them:
VV 52B - at 115mA at 500V on plate, fixed bias (-108V), through a
MagneQuest FS-045 SE OPT, the current draw starts at 110mA and over about
15 min it drops to about 60mA with the bias voltage staying constant. A
couple of soft taps on the side of the top of tube and the current jumps
to 200mA, drops quickly to about 125 mA and the whole process starts
again. The same thing with: a Hammond SE-1627 OPT, AC or DC on filament,
a new tube socket, both tubes do this with one not quite as bad. I'm
afraid to use them and have an expensive set of transformers fried. KR
tubes bought from Welborne Labs.
VV 302B - the most microphonic tubes I have ever seen, the slightest bump
of the tube sounds like a Fender Reverb amp being dropped from 6 inches
onto the floor. Both are bad one is much worse. The tubes sound good but
one bump and expensive speakers could be ruined. KR tubes bought from
Welborne Labs.
AV8B - one tube had several pieces of broken glass in the tube, as a
driver for a 300B; with 350V and 35mA on plate, a 60H choke load, through
a 1uF Jensen foil/paper cap across a 75K ohm 2W carbon comp resister, one
tube would not drive more than about 42VRMS at 1K Hz at 1% THD, the other
would drive 70VRMS. Moth Audio replaced these in 2 days. The new set of
tubes had a completely different internal structure but both worked fine.
AVVT tubes bought from Moth Audio.
KR 2A3 - these were put into an existing SE amp to replace a pair of
Sovtek 2A3s, bias was adjusted for 300V at 50mA on plate and I now have a
great guitar fuzz box. One tube I am getting 1W at 7.5% THD, the other 1W
at about 5% THD. The Sovtek tubes were: 3W at 3.6% THD and 3W at 3.2%
THD. This is with about 12 hours on the tubes, I will let them burn in
for the weekend but I have very low expectations. KR tubes bought from
Welborne Labs.
I would like to think I have had a string of bad luck but I have never
had these kinds of problems with JJ, Svetlana, Sovtek or NOS tubes. The
VV52B and VV302B tubes were out of warranty before I had a chance to use
them so I am out the money for them. The new set of AV8B tubes work fine,
and I will ask for a replacement set of KR 2A3s if they are this bad on
Monday.
So am I unlucky with new European tubes, or, are AVVT and KR over hyped,
overpriced, and poorly made trash?
Joe
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L.J. Timpert
A while ago I purchased AVVT AD100 tubes because I heard from people who were
very satisfied with them, and I had money to burn. Both KR and AVVT have an
excellent reputation.
They never made it into an amplifier. I have the habit of testing all
components thoroughly before I start using them. Electrically, the deviations
of the parameters from the published specs were so large that it couldn't be
understood as normal manufacturing tolerances anymore. I am talking about
doubled plate resistance and half the normal Gm.
Physically, they didn't rattle, but the black plate finish looked very ugly
and the cooling fins were not straight and the welds were ugly too. One tube
showed a fingerprint in the plate coating. They claim that the tubes are
visually inspected, but what are the test standards?
I was too impatient to wait for replacements, so I got my money back. Hearing
your story and considering the fact that Moth now supplies its products
without output tubes I am glad that I have again money and no AVVT tubes. One
thing: the service of the person I bought them from has been good all the
time.
A friend also bought AVVT AD100 tubes and had exactly the same problems. You
are not alone.
I am really wondering what they are doing there in eastern Europe. Both
brands have quite a good reputation. They both claim that the tubes are
extensively tested and matched before they leave the factory. During testing
and burn-in they should have noticed that the tubes were all over the place
electrically, right? Then why did they still sell them? It seems like a very
unwise thing to to for brands with such a good reputation. It might be that
they are experiencing temporary problems, so someone with in-depth knowledge
about these brands could do a great job for them by enlightening this.
Jurgen Timpert
Patrick Turner
and will always say how good they always are.
Unfortunately, it probably doesn't take too many idiots to lead to the
sort of posting we have that casts doubt on a company's reputation.
Who knows, maybe the quality control guy stays drunk all day.
I had 3 out of twelve Tesla EL34 tubes go beserko when I bought
some from a colleague. He had to send the 150 tubes back that he'd
bought. Prior to that, Tesla were renowned to make really decent EL34.
The only thing that stays the same is that change always occurs.
No wonder some people accept SS.
Patrick Turner.
L.J. Timpert
Of course, infant mortality is a known problem in tubes and it can not be
completely "tested out" as there are always some tubes that live long enough to
just survive the tests. It is all a matter of statistics vs. economics, the longer
and more rigorously you test, the less infant mortality you will likely have, but
the more expensive tubes get. Sometimes, there is bad luck, I completely agree.
But not in this case. It was no bad luck. A tube doesn't go into the box testing
and looking good, and come out of the box a few months later testing and looking
bad. This was no infant mortality, as on the test certificates of my tubes it could
clearly be seen that the test results were erroneous. Yet they were still sold.
If you had read my entire post, then you would have known that I didn't say AVVT
tubes and KR tubes are bad tubes. But they clearly have a quality issue here that
is larger than just a bunch of tubes that was not up to regular standard, otherwise
Moth wouldn't have stopped supplying these tubes. And if the quality control guy
stays drunk all day like in your example, he should be sent to an anti-alcohol
course, and not stay in his position. It is their carelessness that casts doubt on
their reputation, not posts like these. They are merely a result of this
carelessness.
But the problem might be temporary. If the quality of their tubes gets up to their
former standard, then everything is OK, right? If the manufacturer tells (on their
website or through their distributors or whatever) that there have been quality
problems, they are solved now and that everty tube from that period may be
exchanged for a good one free of charge, then their reputation will hardly be
dented. This happens in almost all categories of industry. Every manufacturer makes
mistakes. But they must be signaled, otherwise they get away with it.
Jurgen
GRANT G 10
early 20's to late 80's have proven very reliable for me...
-Grant
L.J. Timpert
Svetlana and many other brands. All tested and found good, no exception. And cheap.
Jurgen
Patrick Turner
The Internet is a worldly place where all opinions are put,
and your previous posting and this one of yours are perfectly sensible
and well reasoned.
I agree with what you are saying, and tube manufacturers everywhere
should take heed from what we are saying.
But do they even tune in?
Where are their postings to ask what folks out there think of their
gear? How would they know what to develop next,
if they don't talk with us. And I mean with us,
not down at us, there is a difference.
I would think the High End brigade would be interested.
In fact the Internet is a place where you have to be careful with
people you deal with, or else your name quickly turns to mud, which
tends to stick. It seems so easy for someone to post a complaint.
The Net brings all sorts of freedoms and rights,
but also the big duty of care.
I have no idea if my postulation about a drunk quality control fellow
had any validity, but how else do crook tubes escape a factory?
If I was in charge I would find it easy to at least test one in five of all tubes.
If there was no greater variations in Gm or Ra than 5% in all the tests, it would be
unlikely that there would ever be more.
But I am too young to know first hand what tests were performed at the factories in the
old days. I don't know how Sovtek seem to maintain their standards.
Perhaps someone would like to offer what should be done to change the situation.
Perhaps you should email the makers and invite them here to talk about their
tube products and also tell them that there is some evidence that all is not well
at the present time with quality control.
I am not much good at telling how much I like someone's product,
and then saying that there are problems.
And I've never bought any of the AVVT AD100 tubes,
and I don't know anyone who has.
Often they may take some time before they agree with your test results.
Most drunks spend their sober hours denying that they ever drink or that there
are any problems, it is a widespread bother.
I complained about some dodgy RCA sockets to a store here and
sure that batch was recalled, but the same type remains onsale.
When I suggested a remedy in the form of a steel spring around the internal
pin gripper it was like talking to a brick wall.
They sure were not interested in improving the quality from the Taiwanese
factory. Sometimes you just got to give some things a miss, and shop elsewhere.
A few peolple like yourself and myself just can't be easily conned,
but the others out there who don't know so much are easy targets.
Patrick Turner
I bought a book titled Electronic Equipment Reliability by G.W.A.Dummer and
N.Griffin, published in 1960.
In it are charts on random failure rates of all sorts of tube gear,
with the emphasis on military gear.
The U.S. Navy was appalled to learn that only 33% of its
equipment was operational in 1950, and although the book
does not say so, it looks certain that if World War Three
had broken out then we would only had a third of a war,
as the gear would have failed for most of the time.
Tubes cop a real blast in this book, especially radar
output types on ships.
But little 6J6 tubes were a bother too.
And all the others were a problem as the demands went higher.
And as aircraft went higher and faster, cooling tubes became a designer's
nightmare. Early solid state was at first a pretty sordid tale, but gradually
the reliability of SS far outstripped any tube circuitry.
The most reliable tube circuits were in early computors;
there is a sample of one still in working order at an institution here,
and I think it has about 10,000 tubes in it, which are mainly old,
and some of which keep failing, despite the lack of stress, fine sockets,
airconditioned comfort, and moly codling they recieve.
And tubes fail in storage.
Open an old box of 30 yo tubes and sure enough
there will be some white ones due to vacuum failure or glass
cracks.
None of the problems tubes exhibit put me off using them.
The failure rates in well designed audio gear are similar to old computors,
and I am not using 10,000 tubes.
And in any case the reliability of consumer grade audio gear is so
appalling, along with repairability problems that I am going to stick
with tubes, and I don't see much difference between NOS and
ones made today. A tube failure is rare and a minor inconvenience,
and that is all. I must admit I don't use too many new little ones,
but nearly all the big ones are recently made.
The book does not address the fact well enough that most tube failures
are not due to tubes but due to surrounding component failure.
And service personell would replace a tube and be seen to be busy,
when in fact it was a dogy cap or resistor which takes time to find.
It took one service person for every 250 tubes on an aircraft carrier,
in 1955. And there were thousands of tubes, all over the ship.
So the books attempt to tell the sad story can give us a little
more faith than we could otherwise have.
But there is still the undeniable fact that some old things you buy
just won't go very long.
I do not mind.I don't expect the world to be perfect.
Just imagine if the transistor had been invented in 1903,
instead of the triode.
None of us would be here, others would be, but
history would have been completely different.
I once put a British input tube, an American phase inverter,
and new Russian set of output tubes in an amp.
After a week the american put on a veto and shortcircuited its
cathode to the heater. All was well when I put in an Australian made
inverter to stop all the bulltwang between the Ruskies and the yanks.
Patrick Turner.
L.J. Timpert
I'll add some comments to your text.
Patrick Turner wrote:
> It was not your postings which unjustly casts any sort of doubt.
> The Internet is a worldly place where all opinions are put,
> and your previous posting and this one of yours are perfectly sensible
> and well reasoned.
> I agree with what you are saying, and tube manufacturers everywhere
> should take heed from what we are saying.
> But do they even tune in?
Yes. Jac Music is the world wide distributor of AVVT and Vaic tubes (both brands are
supposed to be unrelated) and he recently posted in this group. Not about his products, he
was searching a Sofia tester. So he is here. Also he posts in the audio asylum. There he
reacted to comments about the price of a product.
>
> Where are their postings to ask what folks out there think of their
> gear? How would they know what to develop next,
> if they don't talk with us.
I think that they just develop something that they think we will want and see if we buy it.
With clever marketing, a seller will make us want his product. Sometimes they are
successful, sometimes they aren't. Some more two-way communication could indeed gain more
understanding about the needs of the customers and about the potential of the manufacturer.
But I am afraid we are being too idealistic here.
> And I mean with us,
> not down at us, there is a difference.
> I would think the High End brigade would be interested.
Well, I think many high-end people have not the capability to be technical about anything,
let alone to do measurements. When there is some quasi-technical talk with the conclusion
that is sounds good, it usually does the trick for most high-end folks. Many traders rely
on this. It is sad, because that also in a way eliminates the need to perform.
>
>
> In fact the Internet is a place where you have to be careful with
> people you deal with, or else your name quickly turns to mud, which
> tends to stick. It seems so easy for someone to post a complaint.
> The Net brings all sorts of freedoms and rights,
> but also the big duty of care.
Yes, it does. It is true that a reputation is easily established and just as easily ruined.
The tube loving internet community is small, and news spreads rapidly. You should be
careful about your actions, both as a trader and as a customer. I have the impression that
many AVVT and KR tubes are sold thanks to the internet, so the manufacturer should be aware
of this fact as well.
>
>
> I have no idea if my postulation about a drunk quality control fellow
> had any validity, but how else do crook tubes escape a factory?
That was the thing that baffled me most as well.
>
> If I was in charge I would find it easy to at least test one in five of all tubes.
Both AVVT and KR claim that they test every single tube. Each tube has a test certificate
with short test results on it. It is quite standard practice for DHT's. Svetlana does this
as well. On their spec sheet, the margins for a good tube are indicated, so there can be no
dispute about testing standards.
>
> If there was no greater variations in Gm or Ra than 5% in all the tests, it would be
> unlikely that there would ever be more.
Yes, and if a bad one would slip out, there should always be tubes in stock to replace it
immediately.
>
> But I am too young to know first hand what tests were performed at the factories in the
>
> old days.
I don't know first hand as well, but I do know some folks who were involved in tube
production back when they were still common. Individual testing was done on even the
cheapest tubes. Their labourers were very skilled and had equipment to test a whole bunch
of tubes in one run and immediately find the crooks. Sometimes they had high dropout rates,
especially when they were making a small run of less common types. But if you can't handle
that, you shouldn't be manufacturing tubes!
> I don't know how Sovtek seem to maintain their standards.
> Perhaps someone would like to offer what should be done to change the situation.
They could start by clearly defining (and publishing) the criteria for a good tube. And
stick to these criteria. Then it is simple, let only those tubes out of the factory that
satisfy these criteria, and destroy the crooks.
>
>
> Perhaps you should email the makers and invite them here to talk about their
> tube products and also tell them that there is some evidence that all is not well
> at the present time with quality control.
> I am not much good at telling how much I like someone's product,
> and then saying that there are problems.
I had exactly the same problem. I really thought their products were worth the effort, both
from their data and from others' opinions. But as a customer I don't feel I am in the
position to tell a manufacturer how to do quality control. They apperently did great in the
past, given their reputation, so they should know it already.
>
>
> And I've never bought any of the AVVT AD100 tubes,
> and I don't know anyone who has.
It is a not so well known tube, but their data looks really promising, like lower Rp than
the 300B and somewhat higher transconductance. And great linearity. It has 4V 2.2A
filaments, so it can not be used in a 300B amp without provisions, but it is quite
interesting for DIY-ers when the power supply transformer is made to spec.
>
> Often they may take some time before they agree with your test results.
> Most drunks spend their sober hours denying that they ever drink or that there
> are any problems, it is a widespread bother.
Yes I have known alcoholic people. It is a very saddening sight and they are not a pleasure
to communicate with. Actually, they are quite depressing, in both drunk and sobre
condition.
>
>
> I complained about some dodgy RCA sockets to a store here and
> sure that batch was recalled, but the same type remains onsale.
> When I suggested a remedy in the form of a steel spring around the internal
> pin gripper it was like talking to a brick wall.
Yes, I also have the feeling that many RCA sockets are a bit crappy. But apperently, the
majority of the customers have no problems with them. And isn't that what counts to many
manufacturers, to keep the quality such that the majority has no complaints?
>
> They sure were not interested in improving the quality from the Taiwanese
> factory. Sometimes you just got to give some things a miss, and shop elsewhere.
> A few peolple like yourself and myself just can't be easily conned,
> but the others out there who don't know so much are easy targets.
I am very critical about the goods I buy, especially about expensive goods. Once the
initial euforia has worn off, I take a critical look at the things I purchased, and I
always find imperfections. Nothing is perfect, and in a sense imperfections give character.
It certainly is so with people, and it is also the case with hand-made products, it shows a
human origin. But with good products all imperfections stay within acceptable limits and
the overall impression is that of a well-made thing. If that is not the case, I don't want
it anymore, especially if it is expensive.
Thank you for your thoughts. Kind regards,
Jurgen Timpert
JHPage
joe...@enteract.com says...
>
> I'm curious if anyone has had any experience with KR or AVVT tubes, I
> have bought 4 pairs of various types and have had problems with all of
> them:
** snip **
I would like to make this clear for the record:
My question here is with the quality of KR and AVVT tubes, NOT with
Welborne Labs or Moth Audio.
I have bought many things form Welborne labs over the last 3 years and
have always had fine service. Ron Welborne is helpful and items are well
packed and shipped quickly.
As I stated in my original post, Moth Audio replaced the bad AV8B tubes
in 2 days with no questions or problems.
Ben Franchuk
(cut)
> instead of the triode.
It could have been the case - people had been claiming
in some cases that cats whisker's diodes did amplify before 1949.
Work on better diodes may have developed the first transistor.
--
"We do not inherit our time on this planet from our parents...
We borrow it from our children."
"Luna family of Octal Computers" http://www.jetnet.ab.ca/users/bfranchuk
Updated - Now with schematics.
Gordon Rankin
<joe...@enteract.com> wrote:
Joe, I have used tons of each of these...
> VV 52B - at 115mA at 500V on plate, fixed bias (-108V),
In the KIR, 120ma/500V/6V heater, fixed autobias (adjusts to 120ma
continually). No problems what so ever. I did have a weird problem a
filament came loose in shipping but still worked. But it would short to the
grid ounce and a while. Other than that I have not had any problems.
> VV 302B - the most microphonic tubes I have ever seen,
I would have to agree with this...
> AV8B - one tube had several pieces of broken glass in the tube,
I had really good luck with these as outputs, never a problem.
> KR 2A3 - these were put into an existing SE amp
Funny in my Gemini I found the KR to be very quiet.
--
J. Gordon Rankin
Wavelength Audio
513.271.4186
wau...@cinti.net
www.wavelengthaudio.com