Should have made not of this in the previous message. The markings
appear to be HP 385. Likely part number is 1901-0385

Eric F. Richards wrote:

(Steven Swift) wrote:


Can you get a close up of the numbers? I have a junk box full of odds and
ends of HP diodes.


Not soon. The pic was taken by an experienced tech who took a look at
it as a favor. I'll have to *gently* get it apart myself or ask him to
do so again. He knows his way around RF but was uncomfortable working
on this thing; I'm almost scared spitless.

...the joys of microwave...

--
Eric F. Richards

"The weird part is that I can feel productive even when I'm doomed."
- Dilbert

"Eric F. Richards" wrote in message
...
Should have made not of this in the previous message. The markings
appear to be HP 385. Likely part number is 1901-0385


Eric,

I can confirm that this is/was the right part number. In the '70's a matched
pair was ~UKP 150.

You might try something like a pair of BAR28, if you can get them, (Shottky
barrier - useful to 10GHz) at UKP 0.5 each IMO they would be worth trying.

Good luck,


--
Roger
London UK.

--

Remove XX for correct email address

I haven't seen them blow out from signal generators, but I have from some of
the high output synthesizers that would put out +23dBm. It's too bad that
they couldn't make a more robust mixer....................you would figure
that they would be using at least a Level 17 mixer.

Pete

Fred Abse wrote in message
newsan.2003.08.11.19.58.05.429819.811@cerebrumco nfus.it...
On Sat, 09 Aug 2003 17:52:22 +0100, Pete KE9OA wrote:

It looks like somebody
must have accidently transmitted into this unit.

You don't need to transmit into most older analyzers. Much more than 10dBm
will croak some of them. You could do that with some signal generators.

BTDT

--
Then there's duct tape ...
(Garrison Keillor)

On Mon, 11 Aug 2003 21:40:39 +0100, Fred Abse
wrote:

On Sat, 09 Aug 2003 17:52:22 +0100, Pete KE9OA wrote:

It looks like somebody
must have accidently transmitted into this unit.

You don't need to transmit into most older analyzers. Much more than 10dBm
will croak some of them. You could do that with some signal generators.

BTDT

My 8554B says "Maximum 10 dBm" on the front in big red letters.

There's probably a reason why they put that on the panel.


73 de Leigh W3NLB

I think it must go back to what devices were available at that time; my
8558B specifies no more than +30dBm.

Pete

Leigh W3NLB wrote in message
...
On Mon, 11 Aug 2003 21:40:39 +0100, Fred Abse
wrote:

On Sat, 09 Aug 2003 17:52:22 +0100, Pete KE9OA wrote:

It looks like somebody
must have accidently transmitted into this unit.

You don't need to transmit into most older analyzers. Much more than
10dBm
will croak some of them. You could do that with some signal generators.

BTDT

My 8554B says "Maximum 10 dBm" on the front in big red letters.

There's probably a reason why they put that on the panel.


73 de Leigh W3NLB

you might be better of using a modern SMD dual schottky diode, better
match, lower capacitance etc. You will have to devise some neat way of
fitting them in. Circuit is in series config so try HSMS-2814, or 2 in
one package HSMS-2815. Try Farnell or Newark? for these parts.Yes the
service manual says you need a matched pair of
1902-0385. I suspect a pair of 5082-2835 would do OK also.

Eric F. Richards wrote:
Greetings...

I don't know where to ask this, so I'm shooting for multiple groups.

I purchased an HP 140T mainframe plus spectrum analyzer plugins,
including the 8554B mentioned in the subject, at a hamfest. It turns
out that it is working but is quite "deaf." From asking around I have
been told that this is a common problem for this plugin and the
culprit is the first mixer.

Well... the first mixer is an upconverter to 3 GHz, and one of those
magical microwave "cans" that make no sense to those of us used to
thinking in lower frequencies. The only semiconductors in the can are
a pair of diodes, back to back, with the designation "385" on them.
HP weenies have suggested that it could be short for 1901-0385, but
that part number turns up very few references, and none with the
nature of the diodes and their operating characteristics.

So I'm wondering if anyone out there knows what type of diodes these
are likely to be and what kind of characteristics I should be looking
for in replacement parts.

Does anyone know anything about this dinosaur? Any help would be
appreciated.

Oh, BTW, the rest of the analyzer and frame work fine. I'm using a
borrowed 8553B plugin with it now and getting the results I'd hoped
for. While I don't plan on doing any critical work with it, the 8554B
is a more capable plugin and I do have to return the borrowed one...

Thanks much!

Hi
I don't think your problem is with the first mixer.I just fixed my 8554b it was quite deaf two.I was told the problem was in the first mixer circuit.I check ed out and that was not the problem at all. The problem was R1-10 ohm 1/4 w. on the (Bandwidth switch assembly) resistor was open this resistor supply the -12.6 also check the two fuses on the back of the 8552b f1-1 amp -10 volts supply and f2 1 amp -12.6 volt supply.I'm also sending you a picture of the bandwidth switch assy it will help you locate R1 10 ohms resistor.I'm sure this will fix your problem with your 8554b RF unit.Please e-mail me back and let me no if it worked or not.
Allan
73
N8ZHC


I don't know where to ask this, so I'm shooting for multiple groups.

I purchased an HP 140T mainframe plus spectrum analyzer plugins,
including the 8554B mentioned in the subject, at a hamfest. It turns
out that it is working but is quite "deaf." From asking around I have
been told that this is a common problem for this plugin and the
culprit is the first mixer.

Well... the first mixer is an upconverter to 3 GHz, and one of those
magical microwave "cans" that make no sense to those of us used to
thinking in lower frequencies. The only semiconductors in the can are
a pair of diodes, back to back, with the designation "385" on them.
HP weenies have suggested that it could be short for 1901-0385, but
that part number turns up very few references, and none with the
nature of the diodes and their operating characteristics.

So I'm wondering if anyone out there knows what type of diodes these
are likely to be and what kind of characteristics I should be looking
for in replacement parts.

Does anyone know anything about this dinosaur? Any help would be
appreciated.

Oh, BTW, the rest of the analyzer and frame work fine. I'm using a
borrowed 8553B plugin with it now and getting the results I'd hoped
for. While I don't plan on doing any critical work with it, the 8554B
is a more capable plugin and I do have to return the borrowed one...

Thanks much!

--
Eric F. Richards,
"Nature abhors a vacuum tube." -- J. R. Pierce, Bell Labs, c. 1940[/quote]