[Milsurplus] "Frnge Howl"

[John J Mccarty]

Hello Hue and everyone on the list.

I had the same problem with my BC-474 when I first got it. It still has the
original output transformer. The previous owner was tinkering with the output
stage, a 1DG, and had replaced the pentode plate to screen cap with a unit of a
different value (can’t remember is it was smaller or larger) and then worked up
a shield for the tube using Reynolds’s wrap and rubber bands. I replaced the cap
with one of correct value (the original was long gone) but found that the shield
was critical for keeping the stage from going into screaming fits at higher
volume settings. In my copy of TM11-4006 it talks about a shield that connects
to pin 1 of the tube which should go directly to chassis. Since I didn’t have
this shield, I made one from a section of a tomato sauce can. It’s not as gross
as it sounds. The can is approximately the right height, so you have the
finished edges, and the cut edge took solder very nicely for a smooth finish. I
also soldered a flange at the bottom with a slit in it and it slides under one
of the chassis screws to make the “ground” connection. Quieted the set right
down at all settings of the volume control.

73 and Happy New Year to everyone.


John n9hrt


On 1/1/2011 3:20 PM, Hue Miller wrote:
> On the "Regenrx" list we have been sporadically discussing "fringe howl" in
> regenerative receivers, with - to my mind at least - no definitive 
> conclusion
> as to how it arises. I recall last night that I had in a BC-474 replaced the 
> opened
> output transformer with a replacement from the SCR-274 receiver. With this
> replacement I encountered the "fringe howl" phenomenon, which I solved
> by "de-Qing" the transformer by loading the primary with an R of some
> k-ohms resistance. The tube is the pentode section of the 3A8, I believe.
> I am asking here, just to verify my memory of years ago, has anyone
> else experienced this in the BC-474, or recall that? I am thinking
> Walt Hutchins (sp?) in an ER article might have addressed this also.
> Also, comments on how-why "fringe howl" arises are welcome.
> 
> Also, the memory retrieval pulled up something totally unconnected.
> Anyone else remember that before there were "hippies", there were
> "fringies"? Or was this only a Washington state thing?
> Best New Year's wishes to us all...
> -Hue Miller 
> 
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