[HBR] HBR design

[hbr@mailman.qth.net]

In a message dated 5/12/02 10:53:44 PM Eastern Daylight Time, 
windy10605@juno.com writes:

> Let me ask you a question, Jim. Why wouldn't you use 
>  6BH6 tubes vs the 6BJ6 in the IF amplifiers ....same
>  grid 1 to plate capacitance, higher transconductance,
>  same plate/screen requirements, same filament power,
>  ......adjust the bias and go.

6BJ6 is remote cutoff, 6BH6 is sharp cutoff. 

> 6BH6 tubes are very plentiful today.

They were used as limiters in Motorola and other mobile FM gear. 

--

Sharp cutoff tubes can replace their remote cutoff counterparts in a pinch, 
but there will be some changes in performance. AGC and MGC will be affected 
by the fact that it takes far less bias change to go from full gain to no 
gain with sharp cutoff tubes. Dynamic range and big-signal handling will 
suffer because the sharp cutoff tubes will be easier to push into the 
nonlinear region. 

Tube makers produced many "remote/sharp" pairs. Here are a few:

6BJ6/6BH6
6BA6/6AU6
6EH7/6EJ7
6SK7/6SJ7
6K7/6J7
6D6/6C6
78/77
58/57

to name just a few.

73 de Jim, N2EY