Hi all,
I've begun to think about restoring my found Collins 75S-3B receiver. My work was tossing it from a long-forgotten storage room that was being repurposed, and what you see in the photo is how I found it (dust wiped from tube names and everything--I've been afraid to wipe the dust up in case the lettering goes with it).
My first step is looking for some filters to get me going with this thing, I suppose. I haven't cut into it yet, as I prefer to part-up before putting anything on my bench (having a project in pieces, stalled because of not having a part on hand, makes the bench all but useful).
So, let me know what you've got, and what you want for it. I think I need an SSB filter to start with (FA-style, 455kHz IF, and 2.1kHz I think). Suggestions are also more than welcome for what you think I might need.
If you can't tell, I'm very green with my exposure to communication-type radios, but I'm learning.
Thanks,
Philip.
I've begun to think about restoring my found Collins 75S-3B receiver. My work was tossing it from a long-forgotten storage room that was being repurposed, and what you see in the photo is how I found it (dust wiped from tube names and everything--I've been afraid to wipe the dust up in case the lettering goes with it).
My first step is looking for some filters to get me going with this thing, I suppose. I haven't cut into it yet, as I prefer to part-up before putting anything on my bench (having a project in pieces, stalled because of not having a part on hand, makes the bench all but useful).
So, let me know what you've got, and what you want for it. I think I need an SSB filter to start with (FA-style, 455kHz IF, and 2.1kHz I think). Suggestions are also more than welcome for what you think I might need.
If you can't tell, I'm very green with my exposure to communication-type radios, but I'm learning.
Thanks,
Philip.
Well, this is the probably wrong venue for your inquiry....
Search on the web and you'll find plenty of dedicated Collins sites. There are sites that have many many Collins filters for sale, including the ones for that rig.
The Collins mechanical filters are abundant on the 'bay too. Looks like you have much to work on before dropping in filters in any case...
Search on the web and you'll find plenty of dedicated Collins sites. There are sites that have many many Collins filters for sale, including the ones for that rig.
The Collins mechanical filters are abundant on the 'bay too. Looks like you have much to work on before dropping in filters in any case...
Actually the rig looks ok.
They are 455kc filters, iirc.
Ebay sellers have them, but some older filters have issues because Collins used foam inside the mechanical resonators which can have turned to goo. This is something that happens occasionally, not that much since the cans are hermetically sealed. I found one website where the guy showed a repair.
You only need a 3.x kHz filter to get going.
A little wider is ok...
If you expect to listen to foreign broadcast, the requirement is for AM, and I think the 75S does not "do" AM, the filter for which would be ~10-18kHz width.
You can "zero beat" AM of course, in the SSB mode.
fwiw, you can make the radio work with just a small cap between the "signal" pins of one of the mechanical filter sockets... it will have the selectivity of the IF strip, which will be ok for basic listening and testing.
This is a ham band receiver, unless xtals are installed for other bands...
you can get a lot of info and manuals, schematics, online.
parts are on ebay and QRZ & QTH dot com, both have "classifieds".
This receiver is still in some demand...
Enjoy!
_-_- WB2GCR
They are 455kc filters, iirc.
Ebay sellers have them, but some older filters have issues because Collins used foam inside the mechanical resonators which can have turned to goo. This is something that happens occasionally, not that much since the cans are hermetically sealed. I found one website where the guy showed a repair.
You only need a 3.x kHz filter to get going.
A little wider is ok...
If you expect to listen to foreign broadcast, the requirement is for AM, and I think the 75S does not "do" AM, the filter for which would be ~10-18kHz width.
You can "zero beat" AM of course, in the SSB mode.
fwiw, you can make the radio work with just a small cap between the "signal" pins of one of the mechanical filter sockets... it will have the selectivity of the IF strip, which will be ok for basic listening and testing.
This is a ham band receiver, unless xtals are installed for other bands...
you can get a lot of info and manuals, schematics, online.
parts are on ebay and QRZ & QTH dot com, both have "classifieds".
This receiver is still in some demand...
Enjoy!
_-_- WB2GCR
It's not that bad--some of the controls are damn-near locked up and the filters are gone, but it'll be a straightforward restoration. Tuning it however...
Yes, I've been looking at older/larger style filters to mount on daughter boards and put into the radio. I've found that parts from the former USSR are 450kHz--I think I know the answer, but I'll ask anyway: would these parts do the job?
I'll have to look into that. I think SSB is 2.1kHz...
Sounds like a neat trick! Can any damage be done? (could I sub-in a filter built from passives in place of the mechanical filter?)
This is a ham band receiver, unless xtals are installed for other bands...
you can get a lot of info and manuals, schematics, online.
parts are on ebay and QRZ & QTH dot com, both have "classifieds".
This receiver is still in some demand...
Enjoy!
_-_- WB2GCR
Yes, there seems to be a lot of info on this particular model--seems to still be somewhat in demand! I know visiting hamfests that Collins commands coin, and I nearly fell over when I saw the logo on this thing in the trash heap... !
Can't wait to get my license so I can start to transmit as well. (there was a Heathkit SB-230 in the junk pile as well... !)
Philip.
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I think I found a list of the filters this set can natively use, from Rockwell/Collins Mechanical Filters
Code:
Equipment P/N Type No. Bandwidth
75S-3B/3C 526-9427-000 F455FA-21 1.85
75S-3B/3C 526-9446-000 F455FA-08 0.53
75S-3B/3C 526-9494-000 F455FA-05 0.37
75S-3B/3C 526-9495-000 F455FA-15 1.5
75S-3B/3C 526-9496-000 F455FA-31 3
75S-3B/3C 526-9497-000 F455FA-40 3.8
75S-3B/3C 526-9498-000 F455FA-60 5.675S-3C is AM, CW, LSB and USB. I've had several of them. To me, that doesn't look like an "OK" rig at all. It's obvious that that the pots and misc. hardware needs attention or replacement, and again you may be searching for parts. This is going to be a project no matter how you look at it..
I've actually WASHED Collins rigs with soap and water, BUT can't say I'd recommend that.... looks like that one could use a bath!
On the mechanical filters - yes they can go bad, but really seldom do. of course if you drop one, it's almost certainly a goner. If the condition is questionable, all you need is a signal generator and a scope. Feed 455 kHz in, then vary by the bandwidth and see what you get out. This assuming you've terminated the filter on input and output with the proper tuning load for that filter. They won't resonate properly without it.
btw- I find 6 kHz is wide enough for speech AM, but for high fidelity, yes you'd want a wider bandwidth. However, that Collins 75S-3C rig is not the cleanest sounding to start with, so high fidelity is questionable.. it is a terrific receiver, but has some distortion issues that require mods to get get around.
Again - do yourself a favor and join a group dedicated to Collins rigs. A knowledgeable local elmer is a real plus.
I've actually WASHED Collins rigs with soap and water, BUT can't say I'd recommend that.... looks like that one could use a bath!
On the mechanical filters - yes they can go bad, but really seldom do. of course if you drop one, it's almost certainly a goner. If the condition is questionable, all you need is a signal generator and a scope. Feed 455 kHz in, then vary by the bandwidth and see what you get out. This assuming you've terminated the filter on input and output with the proper tuning load for that filter. They won't resonate properly without it.
btw- I find 6 kHz is wide enough for speech AM, but for high fidelity, yes you'd want a wider bandwidth. However, that Collins 75S-3C rig is not the cleanest sounding to start with, so high fidelity is questionable.. it is a terrific receiver, but has some distortion issues that require mods to get get around.
Again - do yourself a favor and join a group dedicated to Collins rigs. A knowledgeable local elmer is a real plus.
I had a friend who washed his Collins gear in a dishwasher yearly. He pulled off the casing, removed all the tubes and anything else that would obviously dislike water and in it went. (the casing went into the dishwasher too, just seperately) He dried the rig in a convection oven set to 200°F and the door half open. It took a few hours. Minor service (usually replacing a leaky cap) and alignment was needed after every wash.
His gear always looked minty...
His gear always looked minty...
the 2.1kHz wide filter is SSB "battle mode" - very tight, great in pileups or in a croweded band. I prefer somewhat wider myself.
6kHz for AM is super tight. 12kHz is more like it, imo.
there are a number of Collins groups and just "boatanchor" ham groups around. Certainly check them and read up...
The Collins filters want proper termination and levels to work properly.
You have to go and read a bit and see what they want, and then you can pick filters from other sources or sizes.
yes, you could use other size and form factor 455 filters... you really only need ONE filter to make the rig work OK. I'd get the 31 or 40 or a similar one to start with... hyper narrow just isn't essential for most listening. Imo.
_-_-
6kHz for AM is super tight. 12kHz is more like it, imo.
there are a number of Collins groups and just "boatanchor" ham groups around. Certainly check them and read up...
The Collins filters want proper termination and levels to work properly.
You have to go and read a bit and see what they want, and then you can pick filters from other sources or sizes.
yes, you could use other size and form factor 455 filters... you really only need ONE filter to make the rig work OK. I'd get the 31 or 40 or a similar one to start with... hyper narrow just isn't essential for most listening. Imo.
_-_-
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