Variable 6922 heater to cathode voltage limit...?

[ashok]

I found the following ( +ve) voltage limits for the heater to cathode voltage for the 6922 tube.

1. Telefunken 150 V
2. Raytheon 70 V
3. RCA 120 V
4. ( E88CC ) 50 V

Do they really vary so much between different makes?

Does anyone know the published limits for the Sovtek 6922 and Electro-Harmonix 6922 ?
Thanks.

[EC8010]

Originally posted by ashok
Do they really vary so much between different makes

Probably not, but the testing method and limits applied probably do.

[Tubes4e4]

Originally posted by EC8010
Probably not, but the testing method and limits applied probably do.

Indeed.

And moreover, isolation between heater and cathode gets worse over time. Certain datasheets (*) even define one of the "end of life" conditions for that tube via h-k leakage current at stated positive and negative h-k voltages.

So, h-k ratings given by manufaturers really depend on a lot of additional conditions - what they think is acceptable under the circumstances they considered.

Maybe the sometimes very lowish h-k ratings especially found for ECC88 and the like are not oriented so much at actual h-k isolation capabilities, but much more by noise issues and demands - considering the original/native and intentional usage ECC88 was designed for.

Regards,

Tom

(*) F.e, see Philips E188CC datasheet.