[time-nuts] HP5065A Step Recovery Diode, what part#?

Chicken Time chickenclocks at outlook.com
Wed Aug 29 11:02:03 EDT 2018

Hi all,
Seems that two of my replies never went anywhere as the archives
https://lists.febo.com/pipermail/time-nuts_lists.febo.com/2018-August/thread.html only shows my first email and your replies.
1st post:
Thanks for all the replies so far!  Yes, I had to look up and get some some understanding of SRD to make sure it should at least function.  SMTs were the only ones that I could easily find stock and only a couple was in the correct range.  I've seen 3-4 manufacturers that still make axial ones (MA/COM-essentially same PN practically as HP's original, Pulse Microwave, ASI inc), and I heard that they have minimum quantities of somewhere near 250$...  I figure if I knew what part number, some obsolete resellers might have a couple.

This particular Rb has has been on for many months working great (BTW, the First Aid docs are fantastic!), then it suddenly started behaving the way described. Tuning did nothing, swapping cards did nothing, then I had to start swapping RVFR parts where only the SRD swap seemed to help, hence my dilemma.

2nd post
I've looked in service manuals for a few varied Rbs, and found only one that listed the SRD - it's like a secret!   The one I found was SRS's PRS10 which used/uses Pulse Microwave's MP4025 but their input is 359MHz, rather than HP's 60MHz.   It might work too but it's transition lifetime is
Yes, when I swapped out parts I did retune.  At one point I even had to also mess with the 5.315Mhz setting during the swapping as that test involved swapping out the Resonant Cell.    If I were to guess, the poorer quality of the SMT could be due to the package size, either due its own characteristics at drive levels, or the fact that the SMT size messes with the microwave cavity's characteristics.

Based on some research, including HP's 1984_Transistor_and_Diode_Designers_Handbook, p290, the "best suited" HP part in the axial package that I could fine (if using HP's parts) with the largest transition time and can still generate the 6.8GHz would be the 5082-0825.   But that does not match in any way the H391, 391, P391 markings on it. Neither does any of their other part#s.   I suppose I could see if I can find some of those... Perhaps it was a specialty item?

Considering the Super-ized quality we all kinda, would the quality of the SRD makes a difference, that is from batch/batch, mfr/mfr? (assuming it has the right functional characteristics, of course)

-Chickens are more obsessed with time than Humans. Proof: Clock Clock clock
From: time-nuts <time-nuts-bounces at lists.febo.com> on behalf of cdelect at juno.com <cdelect at juno.com>
Sent: Tuesday, August 28, 2018 1:09 PM
To: time-nuts at lists.febo.com
Subject: [time-nuts] HP5065A Step Recovery Diode, what part#?


I'll throw my two bits in!

Diodes from Efratom FRS, FRK, and M100 are made for 60Mhz drive and
probably would be a good fit.

I'll take a look and see if I have any junkers.

All diodes used in Rubidiums are inside the cell oven so operate at a
high temp anyway.

I agree with Ed, swapping A3 modules requires retuning. One tidbit, make
sure the two trim caps are actually rotating! The top rotor can get stuck
and if you force it the screw connection will break. Then you have a
fixed capacitor, not a variable anymore. If you check ahead of time you
can break the rotor free by levering a tool against it laterally.



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