Products > Test Equipment

Hewlett Packard 740B DC Standard Digital Voltmeter (and 740A)

<< < (11/16) > >>

Dave Wise:
Here are pictures of my DIY input and output cables.  Hope this works, preview seems broken.

Dave Wise:
Here's 740B #2 with original jacks for comparison.

And here is my cable pinout.

Oh that didn't edit right, what am I doing?

Dave Wise:
And a text version of my notes.

000LN was omitted from the CODE LIST OF MANUFACTURERS, but it is

Deutsch
MDR07-7P-090 (input), NSN 5935-00-169-9672
MDR07-7PB-090 (output), NSN 5935-00-410-7256

Mounting hole is 0.685" .

AMP CPC Series 2 shell 11 just fits, flange behind panel,
secured with countersunk flat-head 6-32 screws.
Plug P/N is 206434-1.

TODO: Get one Series 2 Keying Plug to prevent input/output cross-mating.

NEW CABLE PINOUT

SHELL CONTACT NUMBERING looking at contact side of plug

 1 2
3 4 5
6 7 8

INPUT
1  2  3  4  5  6  7  8
G  I- C  O  O  X  O  I+

G = Guard
I = Input
C = Chassis
O = Signal Guard.  Continuous version of O+, i.e. 5 wire between
    A11 and K1A.1 and C4.  Plug has these contacts populated but
    not connected to anything.  This shields pin 8 from the rest.
X = No contact

Cable is triax.
Center       = I+
Inner shield = I-
Outer shield = G
Chassis is a separate wire, bundled to the triax with spiral wrap.

OUTPUT
1  2  3  4  5  6  7  8
G  S- C  J  S+ O- J  O+

G = Guard
S = Sense
C = Chassis
J = Jumper between pins 4 and 7 in plug, energizes output relay in jack.
O = Output

Cables are triax.
CABLE 1
Center       = S+
Inner shield = S-
Outer shield = G
CABLE 2
Center       = O+
Inner shield = O-
Outer shield = G
Chassis is a separate wire, bundled to the triax with spiral wrap.

Cables are strain-relieved at boxes by the common plastic strain relief
used on zip cord, with the projection ground down to accommodate the
larger size of our cable without kinking it.  Smaller size relief on
input (1-triax) cable, larger size relief on output (2-triax) cable.

WARNING: Unless you fit the INPUT jack pin 6 with a keying plug
to prevent cross-mating, if the OUTPUT cable is inadvertently
plugged to the INPUT jack, amplifier output voltage will appear
at the OUTPUT box's SENSE+ terminal even when output is disabled.

Dave Wise:
I can't remember where I got the triax.  Some eBay seller I suppose.  The outside jacket is smooth and slippery-feeling like teflon.  The center conductor insulation is thin but I'm sure it was designed to take high voltage because it is covered by a conductive coating.  At the plug and box it's fiddly but essential to scrape it off without nicking the insulation.  Using my Fluke 895A as a high-R ohmmeter, I can't detect any leakage at all.  Virtually all of the instrument's 10+ gigohm input resistance is the connectors or inside the instrument.  The latter is partly the A9 input/range board and the S1 and S2 MODE and RANGE switches, partly the amplifier input current.

beanflying:
Thanks Dave  :-+

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod