[HBR] strange thing

[Walt Hutchens]

Don wondered:

> The input to the LM318 comes off the sec. of the last IF transformer, via a
> 47k resistor.  It has amazing audio--even at high signal levels (4v p/p).  I
> noticed that when I would remove the X10 scope probe from the input to the
> detector, I would get a rather large DROP in audio level--just the reverse of
> what you would think would happen!  So I soldered a 10 meg resistor across a
> 20pf trimmer cap and put that across the input of the LM-318--where I had the
> scope probe....tuning the 20pf cap brought up the audio level by a good 30%!
> Tuning seems very sharp, with the peek at 11.5pf........?

Where did the last IFT go in the original set?  This sounds like you lost
some of the capacitance needed to resonate that secondary and your scope
probe or 11.5 pf cap replaced that.

Walt
KJ4KV