"Edmund H. Ramm" wrote in message
...

Can anyone please enlighten me as to why there is an 8BN8 heated
by only 6.3 instead of 8.4v, i.e. underheated by 25%, used in R2B?

What forced the designers to accept cathode poisoning instead of
using a 6BN8 valve?

73, Eddi ._._.
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Somewhere buried in an old engineering text I've got a discussion of
grid-leak biasing a tube with higher-than-normal resistance (2x to 5x), then
reducing the filament voltage to reduce the contact potential and (I
believe) the tendency of the grid to go into secondary emission and block.
This was used both for noise reduction and to increase the circuit's input
impedance. I'd give you details but I can't find the @$#% book right now!

Is the tube grid-leak biased? Is the bias resistor significantly larger
than 1M-ohm?