Author Topic: HP 8601a substitution for unobtanium IC  (Read 484 times)

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Offline neil

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HP 8601a substitution for unobtanium IC
« on: August 21, 2019, 03:22:53 pm »
Moving along with the HP8601a sweeper (seized attenuator shaft now resolved), it appears that the IC used as the loop amp in the A3 module is deceased. I tried reseating it several times, but no joy. I gather that these are unobtainium, so am wondering about a modern substitute. This sweeper would be for non-critical hobby use.

The amp (labelled "E1" on the schematic) sits in a PLL loop, between a mixer and a divider chain (which starts with a 2.2uF blocking capacitor). It has a +20v power line and signals in the 0.1 to 110 Mhz range. The input is shown as -20 dBm and output at least 2 dBm.

I wonder if I can substitute a modern chip, perhaps a video amp of some sort on a small daughter board, with appropriate voltage-shifting circuitry as needed? Any suggestions for favorite chips?
« Last Edit: August 21, 2019, 03:26:05 pm by neil »
 

Offline fzabkar

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IRe: HP 8601a substitution for unobtanium IC
« Reply #1 on: August 21, 2019, 10:14:54 pm »
I couldn't find the part (1820-0151) in the cross references:

https://www.sphere.bc.ca/download/hp_xref-free.pdf

However, here is something along the lines that you propose as an alternative solution:

https://f6aoj.ao-journal.com/cariboost_files/hp_20hybrid.pdf
 

Online bd139

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Re: HP 8601a substitution for unobtanium IC
« Reply #2 on: August 21, 2019, 10:59:39 pm »
1820-0149 is referenced as well. See: https://susumu-oiso.blog.so-net.ne.jp/2017-04-05 for a substitute. Looks like they used a standard MMIC as a replacement. You will need to use google translate.
 

Offline retrolefty

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Re: HP 8601a substitution for unobtanium IC
« Reply #3 on: August 21, 2019, 11:20:09 pm »
I too own this sweeper and when obtained used had like half output power but otherwise worked fine. Traced with a scope that A3 was not putting out full gain. I added a Mini-circuits standard MMIC  before the input to the hybrid. I just wired it up dead bug style and it seems to work just fine. It's not a lab quality piece, but extremely useful for sweeping filters. The step attenuator is very nice mechanically and electrically.
« Last Edit: August 21, 2019, 11:27:52 pm by retrolefty »
 

Offline neil

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Re: HP 8601a substitution for unobtanium IC
« Reply #4 on: August 22, 2019, 03:08:11 am »
Thanks for all comments.

It certainly looks like a simple mmic amp would be the first thing to try. My first thought was something from Minicircuits, but I don't know if they do small orders. However, Mouser lists a BGA2874 with 31 dB gain over a DC-750 Mhz range, and at the cost of 41 cents in single-unit quantities, it's hard to turn down.
 

Offline Tony_G

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Re: HP 8601a substitution for unobtanium IC
« Reply #5 on: August 22, 2019, 06:33:07 am »
Minicircuits will do small orders. Sometimes they even have dev boards for the part if you want to use one.

TonyG


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