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previous: Chris Hurley One possible disadvantage would be ... -- 10/22/2000 5:11 PM

Re: 6BM8 Vs. 6BQ5

10/22/2000 7:51 PM
Olle	Re: 6BM8 Vs. 6BQ5 I pondered using 6BM8 once. Had a look at the IV curves for zero grid voltage. As far as I can tell they are very different from the 6BQ5 curves. You cannot use a 6BM8 in a 6BQ5 circuit without modifying it. The 6BM8 delivers alot more current at lower screen voltages. Assuming you feed the screens from about the same voltage as the plates you end up with a primary impedance of about 1000 ohms. Not a likely value for a 6BQ5 OT. The acompanying triode is low gain, more like a 12au7 than a 12ax7, which is typical as PI in 6bq5 p-p circuits. /Olof W

10/22/2000 7:51 PM

Olle

Re: 6BM8 Vs. 6BQ5

I pondered using 6BM8 once.
Had a look at the IV curves for zero
grid voltage. As far as I can tell
they are very different from the
6BQ5 curves. You cannot use a 6BM8
in a 6BQ5 circuit without modifying
it.
The 6BM8 delivers alot more
current at lower screen voltages.
Assuming you feed the screens from
about the same voltage as the plates
you end up with a primary impedance
of about 1000 ohms. Not a likely
value for a 6BQ5 OT.
The acompanying triode is low
gain, more like a 12au7 than
a 12ax7, which is typical as PI in
6bq5 p-p circuits.

/Olof W