Russian 6SL7 6H9C/6N9S ?

[Phil_S]

Anyone have experience with these? Are they any good compared to old stock USA production? It seems there are inexpensive ones made in USSR in the '60's floating around.

I prototyped an amp that uses this tube, but I don't want to be buying up NOS USA tubes for silly prices.

The prototype was built from many recycled parts, hence the amp is made from unobtanium. I would like to try another one 100% made of re-obtanium and see if the result is just as good.

For the curious, the amp is not original in design. It consists of the basic Fender front-end tone stack using two sections of a 6SL7, followed by half of a 6SL7 split load or concertina PI, and the finals are cathode biased push-pull 6SN7's wired in parallel with separate cathode resistors so one can be pulled for half power. It puts out a bit over 10W and has tons of clean tone at a reasonable volume. IMO, the all octal look is impressive.

Thanks.

Phil

[Andy Le Blanc]

they're OK, but...... they're not as robust with power handling, and the tone
is a bit lacking compared to NOS. The over quality of construction is sometimes
surprisingly poor, but as you stated, it better than burning thru NOS. The
only other practicality I found was that the need more warm up time, the
large metal structures in the tube make a good deal of noise until they heat.
You might want to invest in "select" tubes to mitigate some of these issues.

[Phil_S]

Hi Andy,
Thanks. I think you just said they sound like poo. This must explain why the USA stock, even used sells for a price. Maybe I'll work on this a bit and see if I can free myself of the octal look. After all, a 6SL7 and 6SN7 amp design ought to work with 5751's and 12AU7's too. Just exploring the possibilities.
Regards,
Phil

[UR12]

Interesting. I have quite a few NOS 6SL7s and most are microphonic /noisey or hiss. I ordered a new Sovtek and I was pleasantly surprised how good it was compared to all of the NOS I had and actually ended up using the Sovtek. YMMV

[Andy Le Blanc]

The Sovtek shares a design feature with the old Tung-Sol label that is not
present in RCA's, Sylvania's, GE's, JAN-CHS, and many NOS. The top mica
spacer has additional mica wings that reduce micro-phonics, but they're
very thin and reduced in size. The GE's are a little better than some, the "teeth"
on the top spacer fill any space between the spacer and envelope, but are more
ridged-ly coupled. The Tung-Sol has mica disc's the size of dimes. NOS tubes
right from the box after long term storage should be put through an aging
and stabilization process to kick off contaminants on the tubes
elements, to insure premium performance. Its not hard to "hot-shot" a tube
and give it a grid and plate step right on the bench.