Russian copies of valves - beware.

[PJC58-Hythe]

I had a pair of Electro Harmonix 7868 Russian copies fail after 30 minutes use in a Jukebox amp I am repairing - yes both valves. See the attached picture.

The original 7868's had gone low emission after 30 years of use so I thought I would try some of the copies - NEVER again. I have put back the originals for now, but I'm desperately looking for a pair genuine 7868's that test OK - I have posted in the wanted section.

[Chris55000]

Hi!

Out of curiosity, in what respects did you find the replacement valves a disaster in your jukebox amplifier?

Chris Williams

PS!

https://reverb.com/uk/item/31975207-..._source=google

Any good?

[PJL]

The purple glow looks like it's gone to air. Did you check the bias conditions and total plate dissipation? The idea of putting 550V on a B9A socket and an absurd amount of heat in such a small envelope must have meant regular service calls.

[sortedradio]

Hi Peter, what model of juke box amp is it?

[joebog1]

They are not B9A bases. They are 9 pin Novar bases.
I have had this happen with Russian valves myself and have written about my experiences in other threads here on the forum. This particular fault is as you say PJL, that the valve has gone to air. I believe ( my opinion only) is that the glass to pin seal has failed, which is common on Russian valves.

See pic which is of RCA 7868 ( left ) and a 6BM8 ( right )

Joe

[Reelman]

Thanks for that Joe, never heard of Novar before so had to look it up.....

Novar B9E base, 9 pins with 1.02 mm diameter in a 17.45 mm pin circle diameter arc.

I love this forum for increasing your knowledge!

Peter

[sortedradio]

As Joe said, I think the problem may be that the valve sockets on the amp are novar type designed for 1.02mm pins, and the EH 7868 valve uses the magnoval type base with 1,27mm pins. If you loosen the pins in the base the EH version fits ok, but if not it can be a very tight fit, and forcing them in can damage the glass to pin seal, which may have happened here.

[Techman]

Absolutely sortedradio!

I've bought a few Russian valves from various valve wheeler dealers in the Ukraine and can't say that I've ever had this particular problem. As has been said in the post above, it's down to the pins being stressed by the valve holder sockets, particularly if the pins aren't absolutely straight before insertion into the base socket. I've had this same thing happen to me in the distant past, and now with particularly tight valve sockets I make sure that I carefully straighten any slightly out of true pins with long nose pliers. Great care has to be taken, as even straightening the pins can cause fracture of the seal between glass and pin, which usually shows up as the valve heats up in the first half hour of use - sometimes in the first five minutes. In the link below, the valve in the picture shows a valve which is almost guaranteed to fail in this way if it were to be inserted with the pins in the state shown:-
http://www.r-type.org/exhib/abv0001.htm

[vidjoman]

I have replaced several of the sockets and 7868 valves in similar amplifiers. The sockets were called B9D. Never had a problem but they were American made. The valves can easily get the unprotected seal damaged as it’s out in the open in the centre of the pins.

[joebog1]

I think, Techman, that buying ex military Russian valves is a very different thing to modern audio valves.
They come with a whole host of manufacturers names printed on them, INCLUDING Mullard, but essentially they come from two factories that I know of! (I may be corrected on that). They all contain LARGE amounts of pixie dust, and lots of smooth subtle sound.
Only second hand electrons are used however, as they are more tame-erer than new electrons which can be quite aggressive and cause crashing noises as they bash into the plate.
Its quite common to have valves that have been glued into bases crooked, and even the valve inserted into the glass envelope can be crooked with consequent bending of mica mounting plates.

ALL jokes aside, I wont warrant any repairs I do where I am forced to use Russian modern valves. I really have been bitten many times using them.


By the way a 7868 is essentially a 6L6 on steroids.


Joe

[lesmw0sec]

Dunno about Russian audio bottles, but I must say tha a GS35B which I bought from a very helpfull chap in Russia has survived abuse in my linear amp since around 2007. Looking at the construction, I'd reckon you could drop it on conrete with no ill effects!

[GrimJosef]

My experience is that modern production valves are in general not quite as durable as ones made when the industry was a thousand (?) times bigger than it is now. Perhaps we shouldn't be surprised at that. But most of the modern stuff is OK as long as it's not thrashed. All Quad's modern valve equipment is shipped out with Russian (or occasionally Chinese) valves in, and that's been the case for at least 20 years or so. If they fell over all the time then we'd have heard about it.

Sometimes valves do fall over rather too often https://forum.audiogon.com/discussio...-amps-pre-amps. But this might be something to do with running the eight 6550 output valves (four in each channel) with 560V on the screen grids when the datasheets say under no circumstances should they have more than 400-500V (depending on manufacturer) on them.

Cheers,

GJ

[Richard_FM]

Are these newly made or NOS valves.

I think it's been mentioned elsewhere that the Soviet Union used valves for along time after solid state amplifiers came along in military hardware because valves had a better chance of working after an electromagnetic pulse, such as one caused by a nuclear explosion.

I assume valves for military purposes were stockpiled in the cold war & these have found their way onto the open market.

[Maarten]

NOS valves could go to air in larger percentages than normal if they're stocked humid and with regular temperature changes.