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?