[Boatanchors] Why Are Tube AVC and DET Diodes Always Bad?

[Ian Wilson]

Interesting. Don't think I've ever bothered to measure the diodes in a
6{S}Q7, for example.
Since the cathode end of the diode is the tube cathode, you should be able
to detach the
wiring from the tube socket connection and insert a SS diode between that
wiring and the
tube cathode connection on the socket. With care you should be able to
leave the socket
connection intact so you can reverse the fix if/when you find a good
replacement tube.

I *think* that tube diodes usually have a larger effective forward voltage
drop, and certainly
have higher dynamic resistance than a semiconductor diode, so the
performance many
change. I wouldn't think this would be a problem with AM detection but it
may change
the AGC behavior somewhat.

PS. Reliable sources tell me that the April 2015 issue of QST will contain
an article
on "Cheap and Easy Multi-dimenstional Time-defused Quadralateraly
Galactic Pi-R-round Cornbread-R-Square Phase-Potentulated Product
Mega-Demod"

73, ian K3IMW

On Sun, Dec 23, 2012 at 7:33 AM, David Stinson <arc5 at ix.netcom.com> wrote:

> Ever notice when you test the tubes from a rig,
> the Detector / AVC diodes in any used tube are nearly always bad?  Is this
> because of the relatively
> small area of cathode dedicated to them, or is there something
> in the design of tube-type detectors/AVC circuits that is
> hard on these elements?
>
> Has someone devised simple, non-destructive ways
> to bypass bad tube detector diodes and do these functions with, say, a
> silicon signal diode, until one can get a NOS tube?
>
> Please- I'm not at all interested in building a "Multi-dimenstional
> Time-defused Quadralateraly
> Galactic Pi-R-round Cornbread-R-Square Phase-Potentulated Product
> Mega-Demod"
> to do the job of simple diode detector.
> I just want to detect an AM signal, not create anti-matter   ;-)
>
> Thanks,
> D.S.
>
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