Melcor (Navy) 5 Compressor Unit AN/GSA-33 - AM1910/G modules

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beezer4

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Hi all,
I'm starting work on a Melcor Navy Department - Bureau of Ships 5 compressor unit. From what I've read, these are from the early 1960s. My initial plan is the recap the unit, adjust frequency response and go from there. Looks like most, if not all the caps are Sprague mil-spec tantalum. I plan to replace the 3 capacitors in the power supply with electrolytic, but unsure if I should go through each unit and replace the tantalums as well.

Has anyone worked on these units before? or have a schematic?

There is a thread on groupdiy (link), but the schematic drawn there looks slightly different than my units.

Not sure how usable they will be for the studio, but figured I'd give them a go.

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abbey road d enfer

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I plan to replace the 3 capacitors in the power supply with electrolytic, but unsure if I should go through each unit and replace the tantalums as well.
Some comments in the other thread indicate that some capacitors will need to be increased for bass extension.
Since the PSU is single-rail, there are less issues with polarity inversion at turn-on/turn-off, so the tants may not need to be replaced.
There is a thread on groupdiy (link), but the schematic drawn there looks slightly different than my units.
Well, it's good starting point for figuring out the differences.
 

Laughing

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I would recommend really looking into the capacitors on there before just tossing them out. Only specific aluminum electrolytic caps leak and dry out badly, primarily the can-style capacitors that have tabs on them (not the screw-terminal ones, those ones are actually perfectly sealed). If your compressor there is military, it's got military caps.

From here, those look like wet slug tantalums, and I've seen those in working equipment, and bought NOS stock from surplus and put it in my own projects, and they work just fine. Wet slug tantalums, as opposed to the dipped yellow or blue or orange tantalums, have self-healing properties that the latter doesn't, which is why they last so damn long, on top of the fact that they're hermetically glass sealed. Personally, I'd just check to make sure your germaniums don't have tin whiskers by checking for shorts between leads, which is actually a common problem with really old transistor radios. But if they're good, you're good.

Edit: Measure those resistors by clipping a lead and checking it. Humidity leaks into them over time and will make their resistance drift wildly. Check one, and if it's more than the rated tolerance out of spec, then you might just have to check all of them.
 

fazer

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That is a very cool looking unit. I think it’s going to take more than changing capacitors to get the frequency response up. Those transformers are only rated to 3K maybe 5K frequency response, hard to read. I believe their for compressing voice transmission so I as to be heard during battle. Still A cool project.
 

mjrippe

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I sold a rack of five earlier this year, kept a couple loose modules for later. The rack was all original and had a high noise floor and was clearly high passed. Definitely do all the 'lytics and upsize the audio caps.
They are supposed be be like solid-state Maxson/Tri-Tronics CAA/FAA, but I could not tell from the condition they were in. And yes, labeled freq response is not always equal to actual response.
You mentioned yours are Melcor (yes, THAT Melcor). They were also made by Stromberg-Carlson and at least a few others.
 

beezer4

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Thanks everyone for the insight and help! I did test the transformers outside the circuit and they are basically flat 20-20k. I've order some caps and will hopefully start working more on them in the next week or two.

Good call on checking resistors. I sometimes default to assume they working and good.

I'll try to provide updates as I work through them.
 

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