[time-nuts] Noisy varactor diodes

paul swed paulswedb at gmail.com
Tue Dec 18 21:51:02 UTC 2012


John 2 with the same type of issue that is bad luck or simply age. Oh my do
I for see this in my future?
I would be willing to bet it exactly looks like your description. I like
the fact that for $1.23 you can get something from digikey. I do tend to
trust them and mouser.
Regards
Paul.

On Tue, Dec 18, 2012 at 4:42 PM, John Miles <jmiles at pop.net> wrote:

> > I was recently repairing a noisy A3 module for an HP 5065A.
>
> >
>
> > The phase modulator has 4 varactor diodes in parallel.
>
> >
>
> > Since I suspected a diode, I removed them one at a time.
>
> >
>
> > Of course it was the last one! Must be a universal rule there!
>
> >
>
> > Anyway here is a PIX of the noise with the diode reverse biased at 20
>
> > volts.
>
> >
>
> > Anybody know where to get an MV840 ???
>
>
>
> www.octopart.com identifies 23 of them in stock at a reseller called 4
> Star
> Electronics.  Bob's idea of trying a power-supply rectifier sounds
> interesting, though.  Failing that, an NTE replacement part for AM radio
> tuning might work, perhaps in a different series/parallel combination.
>
>
>
> Just curious, what was the 5065A acting like with the bad diode?  Mine
> seems
> to run quietly for days at a time, but then occasionally it generates
> excess
> low-level random noise for a period of hours to days (see image).  Every
> time I've tried to get serious about tracking the problem down, it stops
> misbehaving.  Did yours look like this?
>
>
>
>
>
> It's especially annoying now that I finally sprung for a second 5065A,
> which
> seems to behave almost identically...
>
>
>
> -- john
>
> Miles Design LLC
>
>
>
>
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