[time-nuts] "The Penultimate HP5065 A15"

[Poul-Henning Kamp]

The A15 board in one of my 5065s is in bad shape, and I have started
to look at designing a plug-compatible replacement board.

The main reason I dont just repair/replace the A15 is that 
I want to find out how much instability the PSU contributes.

The outline idea currently is:

	LM399 self-biased voltage reference
	    (See: Linear app-note 42, fig 72)

	The ultimate board would use LTZ1000, but I have not quite
	convinced myself yet, even if it would be cute to have a
	HP5065 which delivered both precise frequency and voltage :-)

	Op-amp based C-field driver

	Vishay SMR1DZ resistors for VREF/C-field stability

	C-field polarity switch.  An experiment.  If nothing else
	I will be able to measure the residual magnetic field.

	Optional adjustable C-field.  Optional because the pot may
	degrade the C-field stability.

	Two +20V on-board LM317-style linear regulators, one for
	the lamp, one for the rest.  Split for noise reasons and
	to be able to play with the lamp voltage/power.

        One or two pre-regulator current measurement shunts.

	DC/DC-brick switchmode -20V supply with brutal filtering.

The downside of the two linear +20V regulators is that even with a
heatsink, they will probably get hot-ish if the internal DC bus is
too much over 24VDC.  For this reason, and because I may simply run
out of PCB space, I may leave the bridge rectifier out, so it will
only works with EXT-DC.

I'll post kicad schematic&pcb once I get further.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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