Actually I have had better success with Zener diodes. The 1N47xx series in particular I have used up to VHF with good results. Take a diode with a zener voltage specification 20% above your operating voltage and it may just work.
Didier KO4BB On Tue, Dec 18, 2012 at 1:51 PM, Robert LaJeunesse < rlajeune...@sbcglobal.net> wrote: > Corby, > > FWIW many power rectifiers can be used as decent varactor diodes. The > MV840 is > nominal 100pF at 4V with at least a 2:1 ratio (2.18 typ) from 4 to 25V. The > Vishay FGP50D-E3/54 is typically 100pF at 4V and drops to a shade below > 50pF at > 25V, or just over 2:1. Good news, it is in stock for $1.32 each at Digi-Key > > http://www.digikey.com/product-detail/en/FGP50D-E3%2F54/FGP50D-E3%2F54GICT-ND/2832954 > . > This part is but one example, there are others with similar > characteristics. > The Fairchild SB1100 is typically 110pF at 4V and drops to a shade below > 50pF at > 25V, again just over 2:1. It's even cheaper at $0.52 each in singles. > > > Unfortunately I can't speak for noise, but these are newer technology parts > and may be clean and linear enough to work as a sub, especially since > there are > 3 other MV840s in parallel. > > > Even if only for a test, Hope this helps. > > Bob > > p.s. I've been known to raid dead PC power supplies for diodes not unlike > these. > But then you'd have to look up data sheets or measure the capacitance with > a > bridge somehow. > > > > ________________________________ > From: "cdel...@juno.com" <cdel...@juno.com> > To: time-nuts@febo.com > Sent: Tue, December 18, 2012 1:32:11 PM > Subject: [time-nuts] Noisy varactor diodes > > I was recently repairing a noisy A3 module for an HP 5065A. > ... > Anybody know where to get an MV840 ??? > > Thanks, > > Corby > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.