[time-nuts] "The Penultimate HP5065 A15"

[Bob kb8tq]

Hi

If a more extensive rebuild is in the works …..

+/-20V is (as has been observed) not an ideal voltage for “modern” electronics. 
If you dig into each of the boards, there is a lot of “drop it down right now” regulation
done on a board by board basis. More or less what might be there:

A1 Synth 		
A2 Battery Charger 
A3 60 MHz multiplier
A4 100 KHz divider 
A5 Digital Divider (= clock) 
A6 1 MHz divider
A7 AC amplifier 
A8 Phase detector
A9 Integrator
A10 OCXO
A11 Rb temp control 
A12 Rb assembly
A13 5 MHz buffer
A14 Logic
A15 Power supply
A16 Power for clock 
A17 Terminal board
A18 Jumpers ( = alt for A2)
A19 Led Clock board 

For most uses, A4,A5,A6,A16,and A19 are not required. A2 is just a pair of diodes (A18) rather than
a battery charger. A17 is more part of the wiring harness than anything else. Looking at what’s left:

A1 synth, this seems to be a target for various replacement schemes. Right now, it has a bunch
of positive voltage rails with some circuits running on 20V. Replacement likely would run on <= +12.

A3 Multiplier. Again a target for replacement in some schemes. Same supply as A1 for replacement. 
Existing design runs +20 direct to a lot of circuits. 

A7 AC amplifier. Now runs on +/-20V. Pretty much begs for a modern op-amp based replacement
board. +/-12 probably is fine for that board.  A *good* -15 would work for the existing board with minor
mods. 

A8 Phase detector. Replacement probably is all digital. Now runs on +20V only. 

A9 Later version of the board runs on +/-15. Probably would work fine on a good +/-12 with minor mods

A10 If it’s a 10811, it’s going to need > +18 for the heater and +12 for the OCXO. There are other 
“at least as good” parts that work fine on +12.

A11 Unless you want to redo the heater windings on A12, you are stuck with +20 to +30V. Rest of the board
sort of begs for a modern op-amp approach. 

A12 Lamp assembly is the only load (other than heater windings and C field). It does run on +20V.

A13 +20V taken to +9 for everything on the board. Simple mod to run on +12 (or +15 or +10 …). Replacement 
likely runs on +12

A14 If the upstream boards get changed, this likely does as well. Sort of begs for a $1 MCU and a handful of resistors
as a replacement. 

A15 ( the topic of discussion)

So, there are two “customers” for -20V. Both would be happy with a fairly good -15V instead. If the replacement
OCXO for A10 tunes 0 to 5V, the need for a negative supply becomes a bit unclear. 

There are a couple of places you can’t easily get around 20 to 30V. The heater windings on the physics 
package are the biggie. The Rb lamp driver is probably not worth messing with. 

If you keep A1, A3, A7, or A8, they will need the existing +20V. +12 or +15 makes more sense for their 
replacements. A13 could easily be modified and run on +12 or +15.

====

So why all this long winded yack?

The ultimate need for +20 is really pretty small. The lamp still needs it. The heaters need something 
in that vicinity. They don’t need the super regulation or low noise that the lamp needs.

The -20 probably does at least as well as a -15 V supply, even as the device sits right now.
Long term -15 makes more sense. 

A bulk +12 (and maybe +5) likely take up the heavy lifting for most of the boards once they are 
modified. Indeed they would be useful even on the existing boards. 

Does this change anything you do on the A15 right now? Maybe not. It is worth thinking a bit on though.

Bob





> On Aug 4, 2020, at 6:35 AM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> 
> --------
> Magnus Danielson writes:
> 
>> If that is the range you aim to improve, then I strongly recommend you
>> do re-read the postings I did about phase noise in detector range, as I
>> have showed that phase-noise get's mixed down to DC and increase the
>> noise there. With very ugly and hand-wavey hack I was able to
>> significantly reduce that noise essentially by cleaning up the
>> phase-noise.
> 
> Ohh, absolutely.
> 
> My plan is to put a modulated DDS synth in to get a much more modern
> detector system.
> 
> But right now the zener on my a15 is better at measuring temperature
> than holding voltage stable, so I'm addressing that first.
> 
> See the 3rd graph here:
> 
> 	http://phk.freebsd.dk/hacks/HP5065A/20150908_a15/
> 
>>>> I would go for the LTZ1000 if you can. The LM399 has gone out of
>>>> fashion for a reason: [...]
>>> Yes, I know, being also a volt-nut :-)
>> 
>> I have not yet jumped down that rabbit-hole as I am by far not done with
>> the current one. :)
>> 
>> I've been looking at the LTZ1000 and one day I may get some.
> 
> You *really* want the version of it which is packaged in the attractive
> and *incredibly* useful "HP3458A" cabinet :-)
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
> 
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