Opinions on Russian 6P6S (6n6c) 6v6 Tubes

Freddy · Post by **Freddy** » Tue 08/10/10 3:27 pm

I picked up a matched quad of these Russian 6P6S (6n6c) 6V6GT wannabees the other day. They were supposed to be Russian surplus from the 70s - 80s. These are the black glass ones with the clear circle on the top that are floating around fleabay and some of the tube vendors sites. The data sheets I found online were conflicting. One mentioned 350V max plate and 315 max screen. Another had 250V max volts for both plate and screen which is closer to a 6aq5 spec. I did plug a pair briefly into a 6V6GT version of an 18 watt superlite that has 340 volts on the plate. After flipping the amp off standby there was some low volume crackling which sounded like insulation breakdown, so I shut the amp off and pulled them out. Hard to see if they are redplating because of the black coating on the inside. Anyone have any experience with these tubes?

Post by **zaphod_phil** » Tue 08/10/10 3:34 pm

I have been successfully running 6pi6 tubes in my commercial build amps, with 440V on the anodes and 430V on the screen grids. I have had no problems with them at all. Those voltage specs are baloney, as are the voltage specs for regular 6V6s. FYI I have seen NOS Brimar 6V6s, which were simply re-labelled Russian 6pi6s. They have a kind of smokey tone.

Apart from that any tube will sometimes go crackly at whatever voltage you may run them. It's just the way things go....

Freddy · Post by **Freddy** » Tue 08/10/10 7:58 pm

Thanks for the reply zaphod_phil. I did not want to sacrifice an OT to an arcing tube and thought I'd ask for advice. Plugged the other matched pair in the amp and no problems. Checked the bias and it looks OK. One tube from the first pair must be going flakey. It sounds like these tubes would survive the high plate/screen volts found in some of the older Fender amps.

Post by **zaphod_phil** » Tue 08/10/10 10:19 pm

As another tip, I would suggest you not bother getting your tubes matched. It's generally a waste of money, and your amp will have richer harmonics with tubes that are slightly out from each other. Also FYI I once tried a pair of 6pi6s in an amp, where one was labelled Sovtek and one was labelled Brimar, so I'm sure they would have been from completely different batches. But they sounded great together.

Freddy · Post by **Freddy** » Wed 08/11/10 3:07 pm

Yes I have mixed and matched single tubes with some success. Finished up a small 6aq5 pp amp 3-4 weeks ago and had 6 unmatched JAN 6005s that I picked through to find the best combination. The best sounding pair give a little hum in the power section, but there is a clarity to the distortion from the power amp section that sounds unusually good. The distortion clarity could be due to some mismatch...I am pretty sure the low level hum in the power section is.
Bought a quad of 6p14 tubes (these were also matched and I could not pass up the price) along with the 6P6S tubes. Plugged these into a TMB last night and again there was a low level crackling for a few seconds when the amp was flipped off standby. This was on both pairs. After that the problem went away and the amp sounded normal with no redplating or arcing that I could see. Played the amp for another 20 minutes without further problems. These tubes are brighter sounding than any EL84s I have used so far, but not in a bad way. At this point I am thinking that it might be some dust or debris that I stirred up in these tubes by handling them. Thanks for your comments and advice.

John_A · Post by **John_A** » Fri 08/13/10 2:55 pm

[quote="zaphod_phil"]As another tip, I would suggest you not bother getting your tubes matched. It's generally a waste of money, ..........

[/quote]

I bought a lot of 24 NOS Russian 6v6's for use in my JTM-18 (fixed bias) with the bias adjustment all the way down they pulled between 7 and 14 watts, if they are as far out as mine were I would suggest going through them and sorting in to close-ish pairs.

Post by **zaphod_phil** » Fri 08/13/10 3:34 pm

OTOH with the odd pair of 6pi6 valves I previously mentioned, labelled Brimar and a Sovtek, they biased close enough to each other that they ended up being left in the amp and being used for several gigs. I had originally just stuck them in for bench testing the newly-built amp.

tubeswell · Post by **tubeswell** » Thu 09/02/10 5:47 am

For dirt cheap (fake*) tubes they don't sound too bad IMHO. I got a handful of them last year and ran one in a reverb unit for a while. The datasheet specs are very conservative.

* they are beam tetrodes - not pentodes, so in one sense they aren't really 6V6 'equivalents' FWIW

Post by **zaphod_phil** » Thu 09/02/10 7:29 am

* they are beam tetrodes - not pentodes, so in one sense they aren't really 6V6 'equivalents' FWIW

If you go into it, 6V6s are also beam tetrodes, and basically a scaled-down version of the 6L6. The 6pi6 also appears to be a clone of the 6V6.

tubeswell · Post by **tubeswell** » Thu 09/02/10 2:23 pm

zaphod_phil wrote:
* they are beam tetrodes - not pentodes, so in one sense they aren't really 6V6 'equivalents' FWIW
If you go into it, 6V6s are also beam tetrodes, and basically a scaled-down version of the 6L6. The 6pi6 also appears to be a clone of the 6V6.

well strike me! I always assumed that since the Tung-Sol 6V6GTA datasheet shows a beam pentode schematic, that the 6V6GTs were all beam pentodes as well, but I had a second 'look' at the 6V6Gt schematic on the radiotron datasheet just now.

'learn somethin' new everyday

Merlinb · Post by **Merlinb** » Thu 09/02/10 2:54 pm

zaphod_phil wrote:FYI I have seen NOS Brimar 6V6s, which were simply re-labelled Russian 6pi6s.

How'd you know when they're re-labelled Russians?

Post by **zaphod_phil** » Thu 09/02/10 3:18 pm

Also some US data sheets seem to incorrectly label beam tetrodes "beam pentode". It's either a beam tetrode or a its a pentode, not both.

Post by **zaphod_phil** » Thu 09/02/10 3:27 pm

Also some US data sheets seem to incorrectly label beam tetrodes "beam pentode". It's either a beam tetrode or a its a pentode, not both.

How'd you know when they're re-labelled Russians?

I was only able to tell when I placed a Russian-made Sovtek and a Brimar side-by-side, and they were completely identical. However, until I did that I wouldn't have known. The Brimar just said "Foreign Made", but it never crossed my mind it was actually Russian. Valve guru "dot_fret" confirmed that in their latter years Brimar had been relabelling Russian tubes.

Merlinb · Post by **Merlinb** » Thu 09/02/10 3:30 pm

zaphod_phil wrote: The Brimar just said "Foreign Made", but it never crossed my mind it was actually Russian.

Interesting. I have a Brimar 6V6GT that says "Made in USSR", but the glass is blacked so I can't see anything but the top mica.

tubeswell · Post by **tubeswell** » Thu 09/02/10 7:45 pm

zaphod_phil wrote:Also some US data sheets seem to incorrectly label beam tetrodes "beam pentode". It's either a beam tetrode or a its a pentode, not both.

So a 'beam pentode' would technically have those directional 'beam' plates as well as a suppressor grid? (in which case how many electrodes is that really?) Hmmm...

Edit - I realise that I had read that before about 'beam this type' and 'beam that type' of tubes, I just never thought to qualify it when I jumped to the conclusion about the 6V6GT this time around. I better practice engaging the brain more before the fingertips

Shottky · Post by **Shottky** » Thu 09/02/10 9:11 pm

I need some clarification: Is 6P6S the same as 6pi6?

dotfret · Post by **dotfret** » Thu 09/02/10 11:29 pm

er, yes ...

pi in the cyrillic alphabet is expressed as p in the Roman alphabet, so sometimes the designation is written 6pi6s.

A 6pi6, without the C (s) suffix, would be either a Chinese version of the valve, or a "metal can" version.

tubeswell · Post by **tubeswell** » Fri 09/03/10 12:06 am

A bit more on this whole beam pentode/ beam tetrode - not pentode/not beam pentode discussion; I see (after closer hindsight look now that my curiosity has got the better of me) that the JJ6V6S datasheet claims their tube is a 'beam pentode' but the schematic on the datasheet appears to be 'just a pentode' schematic. Anyone pulled apart a jj6V6S to see if there are any beam-focussing plates?

Post by **zaphod_phil** » Fri 09/03/10 8:08 am

No need to. The 6V6 is widely documented in electronics text books as a beam tetrode. It's also helpful to look into the commercial history of the development of beam tetrodes, done jointly by RCA and Marconi. Philips held the patents for the power pentode, which was in wide use in the 1930s. So RCA and Marconi had to find a way to eliminate the kink from the tetrode characteristics without infringing Philips' patents. The beam tetrode is what they came up, first with the KT66 and 6L6, followed closely by the 6V6. The 6V6 featured low heater current requirements, for use in car radio applications.

The term "beam pentode" is some old marketing BS, you will also find on many 6L6 spec sheets, as well as other tetrodes. One other point about the JJ 6V6S - it is widely held not to be a true 6V6, but rather something in between a 6V6 and a 6L6. Its electrode structure is larger than that of other true 6V6s, and looks quite a lot like a 6L6s, and is in fact probably capable of dissipating more power than a regular 6V6. It also has a later breakup than most 6V6s.

Shottky · Post by **Shottky** » Fri 09/03/10 8:11 am

dotfret wrote:er, yes ...

pi in the cyrillic alphabet is expressed as p in the Roman alphabet, so sometimes the designation is written 6pi6s.

A 6pi6, without the C (s) suffix, would be either a Chinese version of the valve, or a "metal can" version.

Ah ha! Thanks for clearing that up.

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Opinions on Russian 6P6S (6n6c) 6v6 Tubes

Opinions on Russian 6P6S (6n6c) 6v6 Tubes