Corrections(?) 6550, 6550 vs KT90
TECH OPS 714-434-2174
>>I strongly suggest you stick with KT90s. They will handle the fairly
>>high plate voltage found in your VTLs. Current Chinese and "Sovtek"
>>6550s and KT88s still have reliability problems in VTL amps. (So I
>>hear..... quite a few VTL owners have weighed in about this...) The
>
>Russian 6550A or B will work perfectly fine in any VTL amp and have NO
>problem at all with high plate or screen volts. We've used thousands of
>them so far with even higher voltages and not had ANY "flamers"
According to Luke ( VTL ) there were TWO different KT90s produced. The
ones with a blue base are not compatible with 6550s ( the socket needs to
be re-wired ). The ones with a red base are pin/functional compatible
( as always - you'll need to check the bias ).
>>I'm not familiar with the Svetlana 6550s. How do the Svetlanas compare
>>to the Sovteks?
>
>They are the same tube from the same factory. Mike Matthews (who coined the
>SOVTEK brand name) cannot import the Svetlana tubes directly right now.
I was told that while they are the same internally, the Svetlana has a more
rugged ceramic base - Sovtek is plastic.
IMHO KT90s are way overpriced. I have run Sovtek 6550s with a pretty
decent load for a year without a single problem ( ARCD250ii amp ).
Cheers,
Rolf
EveAnna Manley
Rolf had mailed me the article below for corrections which I gave, but
apparently he did not get my reply. There are a few severe errors here:
>According to Luke ( VTL ) there were TWO different KT90s produced. The
>ones with a blue base are not compatible with 6550s ( the socket needs to
>be re-wired ). The ones with a red base are pin/functional compatible
>( as always - you'll need to check the bias ).
Note: Don't believe everything you read in print!!!! It's like that old
joke where a message, "Prepare your troops, we're going to advance!" gets
passed along a 100 trench soldiers and by the time it ends up at the
general's ears it has become: "Put on your shoes, we're going to a dance!"
Yes there were two versions but both were standard pin out compatible
with 6550's etc. Base color was always BLACK (Gold Aero did, however
re-base the ones they bought from us with a maroon base which they called
KT99--- same tube.) It's the VTL logo PAINT color which was RED (1st
version) then BLUE (later version).
David's orginal design/spec called
for the KT90 to require less negative bias than the GE6550A's has been at
the time. The later 6550A's were always requiring more and more bias to hold
'em down and more xover distortion resulting... So the first KT90 (reds)
could not always plug into somebody _elses_ a/an/other XYZ amplifier
without a little bias fiddling. Everybody wanted the KT90 by that time so
David changed the spec to make it (a little worse???) directly
plug-in-able into a 6550's socket (yes, still check your bias). This
newer tube was painted with a BLUE logo. How clever.
>>>I'm not familiar with the Svetlana 6550s. How do the Svetlanas compare
>>>to the Sovteks?
>>
>>They are the same tube from the same factory. Mike Matthews (who coined the
>>SOVTEK brand name) cannot import the Svetlana tubes directly right now.
>I was told that while they are the same internally, the Svetlana has a more
>rugged ceramic base - Sovtek is plastic.
As I said, they are the same tubes from the same factory. R&G are the
Svetlana factory output importers now and they are sending us the same tube
Mike Matthews was before. There is NO SOVTEK factory! SOVTEK is a brand
name Mike Matthews created for russian tubes from various factories!
However, the latest batch of 6550's from R&G have a new additional
plate "getter" structure welded on. I have yet to see a ceramic base
shipment of Svetlana 6550's.
>IMHO KT90s are way overpriced. I have run Sovtek 6550s with a pretty
>decent load for a year without a single problem ( ARCD250ii amp ).
In my certain knowledge, the KT90 kick the s__t out of any chinese,
russian, or USA made power tube of that 6550/KT88 family! The russian
6550's have been reliable, but they are not a KT90. The only reason that
KT90's are expensive right now is because there are hardly any available
in this country--- Yugoslav EMBARGO, remember? No tube is worth going to
jail for!
We all hear talk of the "next" KT90 out of wherever factory. Pray, hope,
then test....
--
EveAnna Manley--------||------ema...@netcom.com Manley Laboratories, Inc.
13880 Magnolia Ave. Tel:(909)627-4256
Chino, CA. 91710 USA Fax:(909)628-2482
Kerry Davison
>russian, or USA made power tube of that 6550/KT88 family! The russian
>6550's have been reliable, but they are not a KT90. The only reason that
>KT90's are expensive right now is because there are hardly any available
>in this country--- Yugoslav EMBARGO, remember? No tube is worth going to
>jail for!
>We all hear talk of the "next" KT90 out of wherever factory. Pray, hope,
>then test....
[quoted signature nuked by RD]
I'd have to agree with you assesemnent of the KT90 kicking the
excrement out of Russian 6550 tubes. At least that is my experience
using Gold Aero KT99's in Cary SLM SLM-100 monoblocks. The seem to
last a real long time too, so they might not be that bad of an
investment for someone who doesn't trade in their equipment very
often. I also like the Tesla EL34L's in those amps, although Cary
certainly doesn't encourage EL34's in SLM-100's. I'm not sure why
not, maybe they won't last long. They do seem to run hot and glow
very brightly. At $100 for an octet they seem worth experiemnting
with though -- if your amp will take 'em.
BTW, I when I visited Singapore recently, I found that Yugo KT90's are
still available there, imported by Jadis, Richardson, and maybe
others. I was told that Singapore does not have a trade emargo
against Serbain products. But still they are only somewhat cheaper
than typical US prices.
Now a question -- has anyone heard the new Gold Dragon KT90's? If so,
how do they stack up with the EI Yugos? Tony at Handmade tells me
that one he has gotten some customer feedback that they beat the
Russian 6550B's but they weren't compared directly against the Yugo
KT90/99's.
Kerry Davison k.l.d...@att.com
Kevin Hayes
>how do they stack up with the EI Yugos? Tony at Handmade tells me
>that one he has gotten some customer feedback that they beat the
>Russian 6550B's but they weren't compared directly against the Yugo
>KT90/99's.
Well, as US importer for Golden Dragon, I can tell you the following
about the sound of the new KT90
:
1) Curve tracings look very good, basically like a KT88 (slightly more
rounded in the "knee") and with a similar idle point, but with a much
more robust anode, screen grid, & bottle. In other words, PM designed
this tube ti live up to the original claim for the Yugo of being like an
uprated KT88. The original Yugo missed the target in some designers' view
( won't rehash that), although the second generation tube (best known as
the Gold Aero KT99A) was good except for a much lower idle point than a
bogey KT88.
2) Reports of sound preference vary. One very famous *class a* amp
importer tried them and loved them, but a reviewer doing one of their
pieces didn't...these reports seem, as always, to be a function of system
matching and personal preference. This reviewer liked the new Dragon KT88
better.
3) To my ear, the Dragon KT90 puts more of its priority on dynamics from
the middle of the bass through the top of the "chest" range. The new
Dragon KT88 preserves definition at the frequency extremes better and is
slightly more lean through the midband.
4) The type is still new, and we're still gathering observations from
users. Like you, our fingers are crossed...the world needs more good
audio tubes!
I appreciate feedback from all users of the new KT90 and titanium anode
KT90LX, both good and bad, which helps the Dragon folks to make better
and better tubes.
Kevin Hayes
Mitsuo Sakamoto
: Now a question -- has anyone heard the new Gold Dragon KT90's? If so,
: how do they stack up with the EI Yugos? Tony at Handmade tells me
: that one he has gotten some customer feedback that they beat the
: Russian 6550B's but they weren't compared directly against the Yugo
: KT90/99's.
Is there anyone who knows true story of GD KT90 just like
EveAnna Manley told the Yugo KT90 design/specs?
[Moderator note: most of this information can be found in a previous post
in this thread from Kevin Hayes, US importer for GD. --dsb]
Here in Japan, we are talking about GD KT90 now. I am curious
to know whether GD KT90 is electrically compatible with the Yugos
KT90 or not. Some tube dealer says GD KT90 would be the improved
version of KT88 with leverage Telefunken EL156 construction. Is
this true?
Many thanks,
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Mitsuo Sakamoto Yokogawa-Hewlett-Packard, Ltd. Tokyo, Japan