-ex- wrote:
Scott Dorsey wrote:

Depends on the tube, basically. The 3-500Z is a well-implemented design,
but the 6146es still don't meet original spec. And the Chinese 6550
specifically says on the data sheet not to put more than 250V on the plate,
which effectively makes it unusable in anything designed for the 6550.
But on the other hand, the Chinese 211 and 833 tubes seem just fine.

Is this true for all the Chinese tubes? I note there are at least a
couple factories (Liuzhou, Shuguang-Samsung) and at least a few
different brands of the 6550 (ValveArt, Groove Tube). Can they all be
considered as equals?

As far as I know, all of the 6550 tubes, as well as the fake KT-88 that
is not even remotely a KT-88 design, are made all in one factory.

Then again, I thought the Shuguang plant had been bulldozered a few
years back, too.

But everyone and is brother are importing the things... they show up on
this shores under dozens of different names. I've even seen them sold
as Mullard and Amperex... and now there's some guy selling fake Genelex
paper logos that you can glue on them, and fake Genelex boxes to put
them in.

And none of them even come close to meeting the original 6550 specs.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

I have had the filament unsolder to Eimacs in several amps. W6SAI pointed
out the problem in both the 3-400 and 3-500's. My old Henry 2K had the
problem years ago with a 3-400Z. Last year I had problems with Eimac
3-500Z's in my LK-500NTC.

If the tube socket loses its spring grip the filament does not make good
contact and loses its solder. In The Henry, the tube often just popped out
of the socket, With the LK500NTC I still don;t know what the problem is but
suspect the filament transformer may not be balanced so one tube draws too
much current or even the voltage my be say 4V to one tube and 6 violts to
the other rather than 5V to both. The tube is solid in the socket!

To fix YOU MUST use silver solder and a torch. No soldering iron or gun
will do the job!

Dave K4JRB