Can anyone tell me where I can get a schematic of the probe for the HP
8405 Vector Voltmeter?

Thanks
Jerry

Can anyone tell me where I can get a schematic of the probe for the HP
8405 Vector Voltmeter?

It can be found in the scanned copy of the ops-and-service manual for
the 8405, which is in the HP section of the Boat Anchor Manual Archive
site and its mirror.

Look for the 8405_service_6.pdf manual. The quality isn't great (a
somewhat fuzzy scan of the Army-depot version of the HP manual,
partially optical-character-converted into DejaVu and then turned into
PDF) but it's probably usable.

From what I've read (I just bought one of these and am starting the
test-and-refurbish process) the matched diodes are the most vulnerable
components in the probes. The original parts are HP house-numbered
and I assume they're no longer available. Some people have
substituted 1N5711 Schottky diodes (easily available), others suggest
1N270 (gold-doped RF germanium diodes, still available), one gent
suggested the HP/Agilent 5082-2815 which seems to be a matched-quad
set of 5082-2811 Schottky diodes. The latter are probably the most
sensitive but I'm a bit concerned about their low breakdown voltage.
The 1N5711s have a higher threshold voltage but are a lot more rugged,
I expect... don't know if they'll perform as well at high frequencies
as the originals (whatever they are) or the alternatives. Other
high-speed, low-threshold diodes (e.g. those intended for RF mixer and
detector applications) could probably be used. No matter what you
use, hand-matching pairs or quads would probably be a good idea.

The P-channel JFET in the probe was reported by one writer to be a
2N3379 but I don't know if that's correct. Possibly something like a
MMBF546x part might be substituted?

The input capacitor is also sometimes damaged by overvoltage, I
gather, and may need to be replaced as well.

There's a guy on eBay who sells a probe-repair kit... 8 diodes, 2
FETs, and instructions on doing the repair.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Sat, 31 Dec 2005 05:13:23 GMT, "Jerry Martes"
wrote:

Can anyone tell me where I can get a schematic of the probe for the HP
8405 Vector Voltmeter?

www.qsl.net/n7ws/8405_Probe.pdf

Thanks Dave, I really appreciate your info about choosing the components
for these probes. I dont have the skills needed to build something like
this. I depend on being fed information from guys like you, and I
appreciate your input.
I did download a manual from BAMA. I thought I'd read it, but must have
missed the probe schematic.

Thanks again
Jerry





"Dave Platt" wrote in message
...
Can anyone tell me where I can get a schematic of the probe for the HP
8405 Vector Voltmeter?

It can be found in the scanned copy of the ops-and-service manual for
the 8405, which is in the HP section of the Boat Anchor Manual Archive
site and its mirror.

Look for the 8405_service_6.pdf manual. The quality isn't great (a
somewhat fuzzy scan of the Army-depot version of the HP manual,
partially optical-character-converted into DejaVu and then turned into
PDF) but it's probably usable.

From what I've read (I just bought one of these and am starting the
test-and-refurbish process) the matched diodes are the most vulnerable
components in the probes. The original parts are HP house-numbered
and I assume they're no longer available. Some people have
substituted 1N5711 Schottky diodes (easily available), others suggest
1N270 (gold-doped RF germanium diodes, still available), one gent
suggested the HP/Agilent 5082-2815 which seems to be a matched-quad
set of 5082-2811 Schottky diodes. The latter are probably the most
sensitive but I'm a bit concerned about their low breakdown voltage.
The 1N5711s have a higher threshold voltage but are a lot more rugged,
I expect... don't know if they'll perform as well at high frequencies
as the originals (whatever they are) or the alternatives. Other
high-speed, low-threshold diodes (e.g. those intended for RF mixer and
detector applications) could probably be used. No matter what you
use, hand-matching pairs or quads would probably be a good idea.

The P-channel JFET in the probe was reported by one writer to be a
2N3379 but I don't know if that's correct. Possibly something like a
MMBF546x part might be substituted?

The input capacitor is also sometimes damaged by overvoltage, I
gather, and may need to be replaced as well.

There's a guy on eBay who sells a probe-repair kit... 8 diodes, 2
FETs, and instructions on doing the repair.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

"Wes Stewart" wrote in message
...
On Sat, 31 Dec 2005 05:13:23 GMT, "Jerry Martes"
wrote:

Can anyone tell me where I can get a schematic of the probe for the HP
8405 Vector Voltmeter?

www.qsl.net/n7ws/8405_Probe.pdf

Thanks alot Wes
I appreciate your having taken the time to send the probe schematic.

Jerry

Jerry,

I have just completed bringing an 8405a back on line. The BAMA copy is mostly
readable and certainly useable. My unit had a bad probe and a bad pulse
amplifier. Otherwise it aligned very well.

The probes are managable to work. I ended up buying an .024 PC bit to clean the
solder holes. This allowed placing the diodes directly and then soldering them.

The detected phase angle appears to be dependent on having a matched sampling
efficiency between the probes. This is certainly level sensitive and may be
frequency dependent. I have tried several diodes including the origenal HP diodes.

I use a DVM to measure diode forward voltage drop. The origenal diodes measure
about 390 mv. NTE584s measure about 420 mv and can be tuned to match at about
98%. This in practice is usable. 1n5711s measured about 440 mv and can be tuned
to match to about 90%. The instrument will appear work but the phase angles are
incorrect due to the sampling errors. I am still looking for a better choice
then the NTE584s.

Let us know what you find out. - Dan

Jerry Martes wrote:
Can anyone tell me where I can get a schematic of the probe for the HP
8405 Vector Voltmeter?

Thanks
Jerry

"dansawyeror" wrote in message
...
Jerry,

I have just completed bringing an 8405a back on line. The BAMA copy is
mostly readable and certainly useable. My unit had a bad probe and a bad
pulse amplifier. Otherwise it aligned very well.

The probes are managable to work. I ended up buying an .024 PC bit to
clean the solder holes. This allowed placing the diodes directly and then
soldering them.

The detected phase angle appears to be dependent on having a matched
sampling efficiency between the probes. This is certainly level sensitive
and may be frequency dependent. I have tried several diodes including the
origenal HP diodes.

I use a DVM to measure diode forward voltage drop. The origenal diodes
measure about 390 mv. NTE584s measure about 420 mv and can be tuned to
match at about 98%. This in practice is usable. 1n5711s measured about 440
mv and can be tuned to match to about 90%. The instrument will appear work
but the phase angles are incorrect due to the sampling errors. I am still
looking for a better choice then the NTE584s.

Let us know what you find out. - Dan

Hi Dan
I picked the 8405 out of a dumpster at a mil surplus place. Actually I
picked out two HP 8405A Vector Voltmeters. One is complete. The other had
one of its probes severed and I couldnt find that probe. I will try to
build two probes on boards with a BNC in place of the pointed probe.
I dont anticipate being able to make this Voltmeter an accurate
instrument. So, I wont be able to offer any data that anyone else would
want.

Jerry