Russian / Soviet Tubes

[David Root]

Thanx Gimp. Did the Sovietskis not use 12V humbucking heaters?

[TheGimp]

Near as I can tell, most of their tubes were 6.3V heater supply.

Klausmobile has a really good list of tubes and most are 6.3V.

http://klausmobile.narod.ru/td/list_e.htm

[Ian444]

I often wondered how well do the 6N2P stack up against 12AX7? Having some time off, with nothing better to do, reading this forum too much and getting some sort of TW virus, I did an unscientific experiment the last couple of days, that was build up a liverpool cct into an ugly Chinese hifi test chassis using all russian tubes 6N2P-EV and 6P1P-EV outputs using just 2 output tubes instead of 4, so less than 10 watts, a bit like what you did Steve, but with no finesse nor dedication. There were some razor blades in the top end, but then adding the standard liverpool feedback and a Rocket type hi-cut fixed that. Then I rewired the heaters for V1 and swapped out the V1 from 6N2P to 12AX7 Teonex, 5751 Sovtek and 12AT7 RCF. Each tube had its own characteristics, but the 6N2P-EV also has good tone and gain IMO, not too loose, not too bright, it held its own. Just an observation.

Something I noticed about using 6P1P instead of the EL84 (or russian 6P14P) is that the cathode voltage is around 18 to 20V, this would affect the circuit considering EL84's sit around 11V on the cathode, so the PI needs to deliver a higher output swing for max power. Not sure what the consequences of that are, I'll have to think about it. Maybe it means if I rewire the output sockets and put some EL84 in there the amp would have much higher sensitivity, as in, a lot wilder...

[daydreamer]

Man, Ian, I would LOVE to see pics of your test build- that sounds like my kind of amp!!!... ... I'm a sucker for the bitsa look...

[Ian444]

Did I say ugly? Well its been educational at least. Hope to try 6P14P (EL84) today and maybe 6P6S (6V6).

bad and badder

[Cliff Schecht]

I just fired up a Sovtek 12AX7WA (also labeled 7025) and really dug how it sounded in the little amp. Not too harsh, slightly higher noise floor than the RCA 12AX7 I had in there but not at all a bad sounding tube. Also it doesn't have any microphonics problems, this amp will quickly let you know if you do.

[TheGimp]

Ian, I have the 6P1P-EVs biased around 13V with an effective cathode resistance near 360 Ohms, 235V screen supply and 290V B+ (10W dissipation).

I'll probably increase the cathode resistor value next build and up the screen supply at the same time to get closer to 250V on the screens for linearity, without exceeding plate dissipation max (12W).

I'd like to simplify the build by eliminating the bias equalization pot, but will have to match tubes if I'm going to do that.

[daydreamer]

Did I say ugly? Well its been educational at least. Hope to try 6P14P (EL84) today and maybe 6P6S (6V6).

bad and badder

Sweet, you even adapted the PCB, thats very cool thanks for humoring me...

[Ian444]

Hi Gimp, I preferred the sound of seperate cathode resistors to a single shared cathode resistor so went that way. That also makes for easy bias control (well, no bias adjustment). I have found the Russian 6P1P/14P/6S tubes from the 70's and 80's to be very consistent. For example two 6P14P's picked from the same ebay unmatched quad, measured 10.20 and 10.25V at the cathode with 270 ohm bias resistors today. Some 6P6S I bought, 8 off, made 4 nice matched pairs with readings on my tube tester between 47 and 51 from memory (lowest to highest). And when I put them in an amp, that is the real test, I've had no problems with biasing or quality. When I buy from ebay, besides price, I look for shiny pins on the tubes, a sign of good storage conditions.

I managed to get 6P14P's and 6P6S wired up. What did I find, there's not much in it as far as I could discover, the 6P6S have a stronger bottom end, and the 6P1P was warm and sweet. 6P14P has more bite/edge. I guess it depends a lot too on how you tweak the amp to suit, and what sound you like. As I said though, not a lot in it. I wish in hindsight I'd fitted some JJ EL84 I have while the amp was set up for them.

How do you fit an 8-pin tube into a 9-pin socket?

[212Mavguy]

I stuck 6p14p-ev's in my Mesa Maverick and they have been there ever since. They give a more girthy tone than just about any el84's I have used in that amp. I also had my tech install an interesting bias mod, used a vintage Ohmite rheostat in series with a resistor and those two items in parallell with another resistor, (don't remember the values) mounted it to the back of the chassis with a knob on the rheostat, just twist the knob to taste, adjustment is a fairly narrow range, hottest is slightly less hot than mesa setting, which was a tad too hot anyway, coldest still sounds great as well. This amp uses a single cathode bypass resistor for all four output tubes, so the mod replaced that resistor. Has been reliable. Can just reach to the back of the amp and twiddle the knob to taste while playing.

[M Fowler]

I put in a pair of 6P14P into my 18w Rocket but preferred the JJ EL84's
for the smoothness and more pleasing to my ears.

Well we all know how subjective tube choice can be right.

Mark