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

Brooke Clarke brooke at pacific.net
Mon Aug 27 23:11:05 EDT 2018


Diodes that store charge are very different from diodes that do not.  SRD, Varactor & PIN are common diodes that store 
charge. For these the key parameter is the amount of charge storage as measured by the Lifetime specification.  For 
optimum SRD performance you'd like the lifetime to be about 1/4 the period of the drive frequency.  For HF drive 
frequencies that translated to a very long lifetime and probably very hard to find.  Although some Huge Varactor diodes 
with large thread size mounting studs may work well.

I had a conversation with one of the authors of The Art of Electronics and he thought it should be possible to use a 
modern IC to generate a narrow pulse that could replace an SRD for tasks where the input frequency was in the HF range. 
Like the HP 5100.  Note the 5100 has an assembly that's an SRD inside a heater.  The heat increases the lifetime thus 
making for higher output when driven at HF.

Have Fun,

Brooke Clarke
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.

-------- Original Message --------
> Dan
> I missed the fact that you hacked a smt srd in. It was Eds post that caught
> my attention. That hack is worth sharing the details with time-nuts. I
> didn't even know you could get SRDs today.
> Regards
> Paul
> On Mon, Aug 27, 2018 at 8:03 PM, ed breya <eb at telight.com> wrote:
>> I forgot to mention:
>> If you've been diagnosing by swapping parts, be aware that changing the A3
>> is the same as changing the SRD - they won't necessarily match anymore, so
>> would need adjustment.
>> Maybe your original SRD was just fine, but the whole set needed
>> adjustment. Who knows what may have been tweaked or mis-tweaked by
>> individuals working on it previously. If the original SRD is intact, just
>> check to see if it's still a diode (should look the same as a regular Si
>> diode, with maybe a little higher forward voltage drop). If so, it's
>> probably OK and can be returned to service.
>> Ed
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