I posted a few weeks ago about a bad Sovtek El34 that virtually stopped conducting. That left me with a still-working matched pair plus an orphan.
Well, I bought a so-clalled "matched quad" of Svetlana EL34s in Singapore and used those to replace the Sovteks. I swear I can hear no difference in quality between the Svetlanas and Sovteks, despite popular rumours to the contrary. However, the transconductance of the Svetlanas is very low, perhaps around 8 mA/volt instead of 11 mA/volt it should be. Consequently, the bias point of the Svetlanas was very different from that of the Sovteks (which were about normal).
I'm running the EL34s in triode mode, with 360v plate voltage and fixed bias set to give quiescent cathode current of 60mA. I have found that, while one pair of the Svetlanas behaves OK, the other pair is ill-matched and is inclined to drift, so I had to readjust the fixed grid bias for one or both of the tubes in that pair. In the end, I gave up with them and replaced them with the working pair of Sovteks (and readjusted the bias drastically!)
So now I've got the good pair of Svetlanas in one channel and the good pair of Sovteks in the other, albeit with widely different grid bias. It all sounds OK but what a bl**dy state of affairs!
I feel angry about the junk I've managed to collect, acquired from (Indonesian and Singaporean) traders; not that I really blame them, I realize they don't have the education or experience to understand what they're selling. The only advantages of buying in Singapore seem to be cheapness and availability. I can and do blame the Russian manufacturers, though. Don't those bums give a sh*t about the products they let loose on the world?
Well, I bought a so-clalled "matched quad" of Svetlana EL34s in Singapore and used those to replace the Sovteks. I swear I can hear no difference in quality between the Svetlanas and Sovteks, despite popular rumours to the contrary. However, the transconductance of the Svetlanas is very low, perhaps around 8 mA/volt instead of 11 mA/volt it should be. Consequently, the bias point of the Svetlanas was very different from that of the Sovteks (which were about normal).
I'm running the EL34s in triode mode, with 360v plate voltage and fixed bias set to give quiescent cathode current of 60mA. I have found that, while one pair of the Svetlanas behaves OK, the other pair is ill-matched and is inclined to drift, so I had to readjust the fixed grid bias for one or both of the tubes in that pair. In the end, I gave up with them and replaced them with the working pair of Sovteks (and readjusted the bias drastically!)
So now I've got the good pair of Svetlanas in one channel and the good pair of Sovteks in the other, albeit with widely different grid bias. It all sounds OK but what a bl**dy state of affairs!
I feel angry about the junk I've managed to collect, acquired from (Indonesian and Singaporean) traders; not that I really blame them, I realize they don't have the education or experience to understand what they're selling. The only advantages of buying in Singapore seem to be cheapness and availability. I can and do blame the Russian manufacturers, though. Don't those bums give a sh*t about the products they let loose on the world?
Quite a blanket statement! The real Svetlana's i.e. winged C's are great tubes.
Svetlana=Sovtek and Sovtek=Svetlana due to Svetlana USA's buying the rights to the Svetlana name. Conning people into thinking they've got Svetlana's. Well they do...but eh..they don't.
There is no substitute for buying from a good dealer. WHATEVER tube you buy. Whether its Russian, Chinese, European or American.
You're right, Bas, I should have said that I blame the maker(s) of the particular tubes that I bought, not all Russian makers. These are not the "winged C" Svetlanas, by the way. If I'd known more about it when I bought them, I would have chosen differently.
The Singapore dealer seems to have others to choose from, although he didn't say much when I was in his shop. However, I've since been looking at his web site http://www.wellaudiolab.com/
Hi Ray,
That is quit a luxury, being able to walk into a tube shop! LOL.
Good luck..make sure he knows what he is doing. (Ask him how he matches tubes to test his knowledge. 😉
And try to get the winged C's...at least in the States and Europe they look are excellent value for money tubes....
Regards,
Bas
ray_moth said:
So you're running them at a slightly unusual voltage and with fixed bias - I'm not surprised they're not matched. Valves have quite large variations (although not as bad as hfe for bipolar transistors or Vgs for FETs). I'm afraid that once you stray off the beaten path of "normal" operation, you can expect this sort of problem. If you have a really kind valve vendor he might be prepared to match for your precise operating conditions, but be prepared to pay the price - it takes time.
i was talking to the owner of well audio labs today and it seems rare for one to get a pair of faulty tubes since he tests every tube before it gets on the shelves. he labels the transconductance and the current on the boxes too.. so you shouldn`t encounter such problems of instability.
i`ve personally got a quad of svet el34`s from him and they are working perfectly.
i`ve personally got a quad of svet el34`s from him and they are working perfectly.
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