If NOS pre or power tubes became unavailable altogether, what new tubes would you buy?
Thanks, Lowrider. Speaking of terminology, I should be more precise with my own. The number of megohms (millions of ohms) that I referred to as heater-to-cathode leakage is more properly referred to as heater-to-cathode resistance. "Leakage" would more properly refer to the amount of current that would be conducted by that resistance under a given voltage condition. Best regards, -- Al |
Hi Lowrider, Heater-to-cathode leakage is not a specified parameter in the case of most tubes. For example, that parameter does not appear in the GE datasheet that is linked to in Sophia’s description of their 6SN7. Also, it’s not a voltage issue in this case, because even before they were placed in my amp all or nearly all of the eight tubes I received did not meet the 10 megohm criterion that Atmasphere cited as the minimum he would consider to be acceptable. And their measurements did not change much if at all during the time I was using the tubes in my amp. What I and the other member reported in the thread I linked to is either a design issue or a quality control issue, albeit one that apparently would not manifest itself in many applications. Best regards, -- Al |
A cautionary note about the Sophia 6SN7: See the following thread from 2012, in which I and another member both reported that it caused hum problems in our VAC Renaissance amplifiers, which I determined was due to excessive heater-to-cathode leakage. https://forum.audiogon.com/discussions/vac-30-30-sophia-6sn7-s/ As I said in that thread: The heater-to-cathode leakage in my Sophia’s, as measured on my vintage Hickok tube tester, was as low as 3 or 4 megohms on some sections of some of the tubes, and was in the 5 to 10 megohm area on most of the others.I recall that Ralph (Atmasphere) commented some time ago in another thread that he rejects any tube measuring less than 10 megohms. Also, I’ll mention that on my Hickok 800a tester all of the vintage 6SN7 tubes I have measure well above 10 megohms, and in many cases are high enough to be unmeasurable. What I had purchased was a matched quad of Sophia’s "grade A" version of the tube ($100 per tube), with their optional one year warranty ($18 per tube at that time, which I see they’ve increased to $20). To update the history I reported in the other thread, I eventually had Sophia exchange the four tubes for a new matched quad, under the warranty. The replacement tubes worked well for a few months, even though their heater-to-cathode leakage did not measure a great deal better than on the first set. After a few months, though, the replacement tubes developed the same hum problem, and I retired them to my tube collection. If I had speakers that were significantly less efficient (mine are 97.5 db/1 watt/1 meter), or if I had used the tubes in a different amplifier or other component, it seems quite conceivable that I would not have observed this problem. Best regards, -- Al |
