[Milsurplus] BC-348's, remote/sharp cut-off, triode RFA?

[Mike Hanz]

Unserviceable but Repairable wrote:

>Jack on the triode-connected RFA.  That's an oscillation looking for
>a place to happen.  Were triode-connected '348 RFAs neutralized
>

Careful layout.  Langford-Smith talks about this in a number of places, 
e.g., page 1283 of 4th Ed. Radiotron Designer's Handbook  This works 
fine on low power - a grid resistor is the easiest solution but 
apparently wasn't used.

>how the 
>devil to you AVC a triode?
>

Same way you AVC a pentode - page 1111 of 4th Ed. Radiotron Designer's 
Handbook has a hybrid circuit.

>  Did anyone ever make variable-mu triodes?
>

Yup - the best tube I've ever heard of for noise, dynamic range, and 
amplification combined was a 6ES8, intended as a cascode VHF amplifier 
with AVC capability.  One of the last tube designs before  transistors 
took over.  Has a transconductance of 12,500 umhos, an ENR of 160, Noise 
Figure of 6.5dB.  I don't know of any in WWII offhand except triode 
connected pentodes like the 6SK7, however.  I have no idea how the 
triode connection would affect the remote cutoff curve, but I suspect it 
would to some degree - but probably not much.  Obviously it didn't 
eliminate it - the 348 J/N/Q AVC works pretty well for its age.

73,
Mike