[ARC5] [glowbugradio] Suppressor grids and pentodes.

[David Bock]

The SX-140 uses this method as well to good effect.

Dave W8OHS

-----Original Message-----
From: arc5-bounces at mailman.qth.net
[mailto:arc5-bounces at mailman.qth.net]On Behalf Of Kenneth G. Gordon
Sent: Thursday, January 31, 2013 8:47 PM
To: mac
Cc: ARC-5 Mail List
Subject: Re: [ARC5] [glowbugradio] Suppressor grids and pentodes.


On 31 Jan 2013 at 10:35, mac wrote:

> > Ken,
> >
> > Presume the authors meant "will oscillate" if left ungrounded and
> > floating for both DC and RF?

He never menitioned RF...

>  Then I guess they applied a controlled
> >  positive bias to it and got a controlled regeneration
> > characteristic?  Suppressor bypassed to ground for RF in this lash-
> > up?  What was the diode for?  Can you publish the circuit....
> >
> > Dennis D.  W7QHO
> > Glendale, CA

Yes. To all the above questions. The diode was used as a DC controlled
variable resistor between the suppressor and ground.

The controlling element, a 2K pot, was mounted on the front panel, while the
diode and the other bits were mounted at the tube socket.

The diode is connected from the suppressor to ground, Cathode towards
ground. One end of a 1.5 K resistor is connected at the junction of the
diode
and the suppressor. The other end of that resistor is connected to 1) a
10MFD 35V cap with its negative end grounded, and 2) to a line connecting
to the wiper of the 2K pot. The hot end of the pot is connected through a
dropping resistor (100K in this case) to B+. The cold end of the 2K pot is
grounded.

There is no RF bypass capacitor "around" the diode, possibly to enhance
"regeneration". Perhaps it simply wasn't needed. I have not yet tried the
circuit nor closely examined its operation.

As I have time, I'll publish the schematic and other info on my website at
www.w7ekb.com/glowbugs/

Kenneth G. Gordon W7EKB

"Courage is being scared to death but saddling up anyway."--- John   Wayne

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