[ARC5] "Poor Man's Q-multiplier"

[Kenneth G. Gordon]

On 25 Jan 2013 at 10:47, Bill Fuqua wrote:

>     As far as the screen grid goes.
> That is just the usual way it is done.
> The tube data sheets tell you this and the curves always assume this
> as well. Usually the suppressor is connected directly to the cathode
> internally.

I had always assumed that the suppressor was connected to the cathode 
internally only in those tubes which did not have an "extra" pin to connect it 
to externally. I know in beam-power tubes, that is often the case.

> I agree with the first IF being the Q multiplier. I did
> this with my BC-455 and it worked very well. However, you must remove
> the AVC from the tube and provide a separate cathode variable gain
> resistor so you can adjust the gain of the tube. I don't recall the
> article, but I can look it up and see what they did. I was only 2
> years old in 1950.

I was wrong there too: the article was written by Lew McCoy in 1960, not 
1950. I get confused about dates easily. :-)

>  I brought out a wire out of the top of the IF cans
> to make a gimick capacitor that I could adjust to get the feedback in
> the ball park. Wanted it to oscillate when gain was set a little below
> max. The wires were connected to the plate and grid of the tube.
>      Even with the high frequency IF in the BC-455, I was impressed by
>      the
> selectivity it provided. But your AVC action will be reduced.

Many years ago, I used that method with the 1st IF for a BC-454 and it really 
helped on CW. I also did that to a BC-455. It did help there too, but not as 
much as with the lower IF of the BC-454.

In the BC-454, the "other side" of zero beat was down very noticeably from 
"this side": there was a noticeable difference in the BC-455, but it wasn't as 
pronounced.

I even tried it with a BC-453, but it was difficult to get it "centered" in the IF 
passband, which was already pretty selective.

Ken W7EKB