[time-nuts] Replacement A9 boards for the HP 5065A

Charles Steinmetz csteinmetz at yandex.com
Sun Mar 4 16:04:53 EST 2018


Poul-Henning wrote:

> I fully agree, and if it were me, I would absolutely use the best
> capacitor I could find at a non-insane price.
>
> But that was exacly my point:  The only thing you (might!) get by
> spending an *insane* amount of money on that capacitor is PTFE and
> its better dielectric absorption.     *     *     *
> And third, the difference in DA between PTFE and Polystyrene is
> barely a factor five and it is from 0.05%(PS) to 0.01%(PTFE).

I agree, no PTFE (as I said in a previous message) because it is simply 
impractible (or even impossible) to fit on a board that fits into the 
5065A.  But as I said in the same message, that is also true of PS 
(also, I'm not aware of any currently available in integer uF values).

Last I knew, there are (were?) at least 3 reputable suppliers of PTFE 
capacitors, but none of my designs in current production uses them so I 
don't have any recent experience.  I do see that Electrocube still lists 
the 463D series on a web page with a 2018 copyright date.

I concur with everything you say about alleged PTFE caps from 
"alternative" suppliers.

So, no PTFE or PS for practical reasons.  That leaves us with PP, PPS, 
and perhaps PC.  These all have reasonably similar DA, so as long as one 
checks the particular capacitor's datasheet to verify, DA should not be 
much of a factor in choosing between them.

Best regards,

Charles




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