[Collins] wider audio for 51J4?

[joel hallas]

Well, before I found a 6 kHz filter for my J4, I just bridged the filter 
connections with a coupling capacitor across the filter pins, perhaps 
0.01 uF, and then you need to provide both a plate and grid resistor 
(across the narrow pins at each end) so the stages worked. I don't 
remember what values I picked, but don't think they were critical. Tens 
of k on the plate side, 100s of k on the grid side. It worked fine. The 
gain didn't change significantly as I switched between 6, 3 and 1 kHz 
(the other filters were there.

In terms of stagger tuning, I did that a bit as well - the IF 
transformers, as is, are a bit sharp for what you want. I was surprised 
to find that one transformer, perhaps the last one before the detector, 
and I think the bottom slug, made all the difference. It was almost like 
a selectivity control. I'm not sure if it would go to to 12 kHz, but at 
least 8 to 10 without much trouble. I am quite happy with the 6 kHz 
(made from some tiny filter from an ER article) for amateur operation, 
although I guess it doesn't quite do "hi-fi."

GL & 73, Joel

Joel R. Hallas, W1ZR

Eugene Hertz wrote:

>Hello all,
>
>In a discussion with a friend, we were talking about the narrow 6kc filter of the 51J4 and we were wondering can this be replaced with some simple rc filter (or otherwise) for better AM audio bandwidth?  Can 12kc be attained? Whats the most (at the sacrifice of selectivity)?
>
>Anyone have (or can point me to) a circuit diagram for a nice wide output?
>
>thanks!
>Eugene
>PS Someone out there in collins land must have some bad J4 filters,no?
>
>
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