Rerurn to Romy the Cat's Site
In the Forum: Audio For Dummies ™
In the Thread: Get, or made up a tube tester, it’s necessary
Post Subject: Thermal hysteresisPosted by deemon on: 1/24/2007
Hi Jim !
You wrote about "hysteresis" in the 6C33C curves - it seems to be a very interesting point ! Maybe Romy told you about one fault of this kind of tubes - some old ones have a bad tendency of "thermal breakdown" . I mean positive thermal coefficient that may cause very fast ( almost avalanche ) tube overheat . What for me - I noticed it twice when made experiments with 6C33C . And your measurements shows this thermal mechanism . We can suppose that we have some parasitic electron emission from the grid , and when the current grows - the grid temperature ( and this emission ) rises too , but with some time delay . So when the current goes down , the grid temperature is higher than when the current goes up , and we can see this strange "hysteresis" .
Byt what is the cause of this grid electron emission ? One explanation is that some active oxide components from the cathode can "evaporate" and settle on the grid .... who knows , I think that it seems realistic .
Best regards
Dima Rerurn to Romy the Cat's Site