[ARC5] Way Off Topic

[Hubert Miller]

I just want to be clear on this: the grid capacitor affects selectivity too?  That is something i had not expected, nor can i explain it.
The usual grid capacitance in the grid-leak detector circuit is 100 - 150 pF. You VERY rarely see anything else.
-Hue Miller

________________________________
From: on behalf of kgordon2006
Sent: Friday, February 27, 2026 8:14 AM
To: Hubert Miller ; <arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>>
Subject: Re: [ARC5] Way Off Topic

Yes. Many, if not most, regen circuits used a 250 pfd grid cap.

In many discussions with BoatAnchor Bob Keyes, we discovered that reducing the value of that cap very noticably increased selectivity.

Then, adjusting the grid leak resistor to a value much greater than the usual 100 or 150K also improved selectivity, at least on "weak" signals.

Of course, like almost anything else, it is possible to go too far, so experimentation is in order.

I have suspected (but really dont "know") that doing this reduces RF losses in the grid circuit.

Anyway, I know it works, since both Bob and I have experienced it.

Ken W7EKB



Sent from my Galaxy


-------- Original message --------
From: Hubert Miller <Kargo_cult at msn.com<mailto:Kargo_cult at msn.com>>
Date: 2/26/26 23:00 (GMT-08:00)
To: arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>
Subject: Re: [ARC5] Way Off Topic

Thanks for that tip also, Ken. I thought the high meg grid resistor would cause blocking, as in superregeneration.
I had decades ago a Knight Kit Space Spanner regen receiver. Something happened inside the 12AT7 det tube. Whereas before in straight regen mode, it could perfectly separate stations 10 kHz apart in the then crowded 49 meter band, in superrrgen mode the selectivity was more like 100 kHz, there was a weird  "springy" sound, and it was so MUCH louder on the selected station.
I have a kit radio regen for the MWBC band which has a 1000 pF grid cap. Maybe that was to simplify the parts count for beginners, but that seems to me a real mistake, and i want to try it with the more usual value.
-Hue Miller



Sent from my Galaxy


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