[Collins] 6AQ5 v. 6BF5?

[Gerald]

On Tue, 2005-04-26 at 08:47 -0700, C Eus wrote:
> All:
> I took a look at these two tubes on the NJ7P website.
> It looks to me that the 6AQ5 is more robust than the
> 6BF5. My question: is the 6AQ5 close enough to
> substitute for the 6BF5? Certainly the pinouts look
> the same but the 6AQ5 appears "beefier". Your
> comments, please! Cal, n6KYR/8 P.S. I'm considering
> subbing it in the 51S1 audio amp. 

I'm not sure which is beefier. The 6BF5 heater runs 1.2 amps and the
6AQ5 runs 0.45 amps. That hints the 6BF5 has greater emission from the
cathode for higher peak currents or longer life. It does show the 6BF5
dissipates 4.73 watts more power just from the heater. In the 75S-
receivers the tube heaters are all in parallel when running from the AC
supply but are connected in series/parallel for 12 and 24 volt DC
operation. The different current of the 6AQ5 means heater voltages will
be mostly wrong all through the receiver on 12 and 24 volt DC operation.

My RCA tube manual refers to the 6V6GT for typical operation of the 6AQ5
WITHIN RATINGS. It would be easiest for a web page to copy 6V6 typical
operation to 6AQ5 without noting the dissipation and current limits of
the 6AQ5 to make the 6AQ5 look more robust than the 6BF5. I don't see
typical operating conditions for the 6AQ5 at 110 volts on the plate
which is the typical condition for the 6BF5. For the data given the 6AQ5
needs 12.5 volts grid bias and the 6BF5 needs 7.5 volts bias. So it may
be that the 6AQ5 will draw more than typical plate current when biased
as a 6BF5. With the difference in heater power, the 6AQ5 may still run
cooler.

I'm sure the 6AQ5 has been run in 6BF5 sockets.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer