HP 8601a substitution for unobtanium IC

[neil]

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?

[fzabkar]

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

[bd139]

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.

[retrolefty]

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.

[neil]

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.

[Tony_G]

Minicircuits will do small orders. Sometimes they even have dev boards for the part if you want to use one.

TonyG

[djsb]

Did you get this sorted? I might want to buy one of these units. Thanks.

David.