For sale is a matched pair of 6N7S FOTON Tashkent  USSR NOS tube made in 60's,  two tubes with the same or very very close parameters. Tubes are unused, never inserted in socket except testing procedure, high precision tested and very tight demands for matching. Many tubes were tested for this selection, made from 1960 to 1968, at matching in pairs electrical results prevailed in front of "same date", so not all pairs are same date, for example could be pairs a tube from 62 with one from 64, or may 67 with june 67.

Each section of tubes is matched. All offers you can find for this kind of tube and all results from tests are for both section paralleled from a tube. Are not false offers because original datasheet mention those results, even on L3-3 tube tester card, but only to know if a tube is good/bad, not for matching, was a good method when peoples were listening to AM radios with 10% distortions. 

To match double tubes means each of 4 triodes inside to be matched, exact like 6N7G/ECC31 datasheet says and how we tested and selected matched pairs by plate current, transconductance, gain, plate resistance and curves.

6N7S is a tube less known and less appreciated than it deserve, is a wonderful double triode with common cathode that can be used in all stages, preamplifier, driver or output tube, special designated to work in class B (0 to positive grid) in old radios/amplifiers, when class B configuration saves the energy from batteries. But can work in other classes too. 

A pair of tube in PP configuration can deliver 10W less distortion audio power and a PPP configuration 20W.

About equivalencies from title:

- tubes were tested using 6N7G/ECC31 settings on tube tester except grid voltage modified from -4.6V to -3V, 6N7S need less negative voltage for same results;

- 6N7S is a direct replacement for 6N7G, NR73, ECC31, self cathode bias will work nice and for fix bias maybe is needed readjustment;

- the same with 6A6 which is the same tube like 6N7G/ECC31 except different base/socket;

- the same with NR53 that is 6A6 but different heater voltage.

This is an offer for those who want the best possible tubes for their preamp/amp, other way using any unmatched tubes some music can be heard.

All quality tests for tubes were made automatically by Roetest, vacuum, leaks, shorts, heater current etc., all tubes passed these checks.

Tested with Roetest V10, a wonderful german machine for testing tubes, it shows everything about a tube, "the Roll Royce amongst the new production tube testers,  it is at this moment the finest product on the market and nothing will outdo it"[emissionlabs quote].

Just ask if you need more details, we'll answer fast.

 You will love the rich, detailed sound they produce, and the lack of hiss or hum.

We send next day after payment, priority airmail with tracking number. Please be patient with shipping time that can be surprisingly fast or disappointingly slow, depends only by post services.