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Collins S/Line Restoration Notes

By Chris Codella, W2PA

June 2008

The Collins S/Line was the gold standard of amateur radio when I was a teenager starting out in ham radio.  But with lawn-mowing as my only source of income, I could barely manage to afford aluminum.  So as an adult, getting interested in classic equipment of my youth, the S/Line was one setup I knew I had to own eventually.

I purchased this S/Line from its second owner who had in turn bought it a couple of years previously from the widow of its original owner, who had become a silent key a few years before that.  The original owner had been a heavy smoker and never cleaned the rig, so by the time I got it more than 35 years of grime had built up on its surfaces and parts, giving everything a yellowish-brown hue.  Despite this coating I could see that the paint was in very good condition, the units were working and, as a bonus, the receiver came with three IF crystal filters – the 2.1kHz SSB, 500Hz and 200Hz CW filters.  So I bought the package, consisting of a 75S-3B receiver, 32S-3 transmitter, 516F-3 power supply and cabinet, in which a speaker had been mounted.  The package also came with an RF Power Components “Maxi-Tuner” from the 1970s with a cabinet that nearly matched the Collins.  The receiver is a round-emblem (RE) transitional unit – meaning it has the round emblem but there are two small, countersunk Phillips-head screws on either side of the emblem that fill holes originally meant for fastening a winged emblem (WE).  The screw heads are painted to blend into the front panel.Collins did this during the one year of transition from WE to RE.  I guess they had an excess of front panels and couldn’t wait to change over.  Unlike other models, this nails down the date of manufacture to sometime during 1969, just after the tenth anniversary of the S/Line, about midway through its run, and my first year in amateur radio.  The other two units in the package have the winged emblem. I later purchased a 312B-4 console and SM-1 microphone to round out the set.

Click here to follow along with pictures.  This is the best way to view them.

Or watch the mini-slideshow in the Photo Gallery.


75S-3B Receiver

Chassis

To prepare to clean the chassis, I removed all the tubes, filter cover, and filters.  I removed the knobs, either pulling them straight off or loosening setscrews with a Bristol wrench.  I removed the S-meter using a long shafted nut driver – a screwdriver handle with a standard ¼-inch socket end, an 8-inch extension, and the proper size socket.  Next, I removed the dial assembly, fiducial and escutcheon, following the directions in the Collins service bulletin (ASAB 1007, 1011 or 1014 – they’re basically the same).  I removed the pilot light socket from the aluminum bracket above the dial and left it dangling by its wires, tucked away by the rejection tuning can.   The bracket and its spacers were put aside.  After removing the dial it’s a good idea to reinsert the PTO tuning shaft back into the front panel bushing just to keep the PTO from flopping around without its mounting screws.

I tried to remove the preselector rack assembly from the chassis, figuring it would help expose more surfaces and make things more accessible when I got to the cleaning step.  The rack is held in place by four self-tapping screws that go into the chassis, two at the base of each end bracket.  I took all 4 screws out and started to try to remove the rack - but then noticed two things that made me stop until I thought about it more: It’s difficult to pull the three slugs out cleanly with the rack because you must move the rack towards the rear of the chassis in order to get the shaft to clear the front panel.  Second, when I removed the four mounting screws I realized that the bottoms of the two end brackets are held in place solely by those screws and the chassis itself.  If you're not careful and try to lift it out straight, the bottoms of the end brackets swing outward and the main lifting shaft drops off its pivot at the back end, the metal drive straps at each end are no longer under tension, and the whole thing stops working and feels like it'll fall apart.

So I bought a clamp, with plastic pads on the jaws, to hold the sides of the bracket together as it's removed; that way it stays together as a unit.  You have to start with the slugs cranked to their upper most position, be careful to lift the slugs up and out of their coils first, then angle the rack up towards the back to pull the shaft out of the front panel hole.  This worked out fine and allowed me to more easily clean the chassis around the alignment trimmers, and to clean the rack separately by spraying with Krud Kutter and rinsing with water.  The nicotine coating ran off easily without rubbing or brushing.  On some metal parts this process left a whitish residue that I had to wipe off with Q-tips and water.

The alternative might be to just take the whole rack apart - but that would add a lot of additional unknowns I'd have to face and figure out, so I decided against it.  Another alternative, of course, is to leave it in there and clean around it.

I cleaned the knobs using a toothbrush.  Palmolive dish detergent works okay but Windex with vinegar melts away the nicotine stains without even scrubbing.  It also seems to attack old white pointer lines in knobs. I noticed that the knobs have a thin outer layer of black plastic that sometimes flakes off in a small number of places.

The main tuning knob with finger cup comes apart - the knob detaches from the skirt which is glued in place.  Mine came apart while scrubbing with a toothbrush using Windex with vinegar.  It's easily reassembled.

The tubes were rinsed with only water to preserve their markings.  The filter cover was first washed with Windex, which wasn’t quite able to remove the brownish mark on the side, a result of heat enhanced nicotine staining.  A small amount of Fantastik on a paper towel removed it with some rubbing.

The heterodyne oscillator crystals had the same coating of gunk but were harder to clean – possibly because of the metal used to make the crystal holders.  Windex, Fantastik, and Simple Green all had problems – Krud Kutter worked.  I soaked a paper towel with it and rubbed each crystal holder against it for a few seconds, then wiped off with a clean paper towel.

The top surface of the chassis was the dirtiest, coated with a combination of cigarette smoke residue and dust.  I first removed as much of this as possible with a dry Q-tip, then removed the rest with a Q-tip with KK followed by plain water.  I would do a small section at a time, working my way across the chassis surface.  When I came across transformers or other chassis-mounted items, I’d clean them using the same process. The PTO was left connected but unmounted, enabling it to be cleaned easily, also using the same process.

Krud Kutter worked well on the white trimmer capacitors, removing more brownish stains than water and detergent alone.  I used a Q-tip with a little KK, then wiped again with just water.

The chassis underside was partly cleaned using the same process as the top deck, but it had far less nicotine coating, except in specific places such as directly under the dial opening and on the surfaces of the bandswitch shields.

A word or two about Krud Kutter: I like it because it is relatively gentle to most materials including paint and plastic. It's also environmentally friendly, if you can believe the label, and is water soluble.  And it has hardly any smell at all, unlike most other cleaners. Last but not least, it really works well. It makes nicotine and other gunk just flow off.

However, you must be careful using it around certain markings. The main chassis markings, such as tube socket labels, are impervious to it. But the stick-on metal labels, such as the one with the serial number, and chassis labels that look like they were applied with a rubber stamp, will wash off if you use too much KK and rub too hard.


Knobs

The spun aluminum inserts needed to be replaced but are difficult to remove from the knobs that have them.  I drilled a small hole, about 1/8 inch, through the center of the front until I saw black plastic shards coming up from the drill bit.  I then used a small bladed screwdriver to pry up the insert from inside the hole.  They seem to be glued in more solidly than those on the Drake or Heathkit knobs.  I had to work my way around in a circle in the drill hole until the insert starts to come up, then work the screwdriver under it until one outer edge pops up.  You can then easily pry up the rest of it or grab the loose end with pliers and pull it off.  Either way you have to take care not to scratch the rest of the knob.  Then clean and smooth out the surface where the new insert will go to make sure it’s flat and will secure the new insert well.

I polished the knobs with Novus #2 plastic polish using Q-tips and a cloth for buffing.  In the process I learned not to use a lot of pressure with the Q-tips or you end up with swirls in the finish that you’ll have to then polish out by doing it all over again.  Just swirl it around gently until it dries, then buff it off using a cloth.

The main tuning knob consists of two pieces – the knob and the skirt.  Mine came apart as I was polishing it since the glue had become brittle as it aged.  This allowed me to polish the two separate pieces more easily.

After polishing, I repainted the white indicator lines on the knobs that have them.  I used acrylic latex paint, “ultra white” color.  This paint is rather thick so I thinned it a bit with water.  The thinned paint can be applied with a wooden toothpick point.  As you touch the groove for the white line, the paint flows into the groove and spreads up the sides by surface tension.  With experimentation you can get just the right amount in there with minimal excess on the top of the knob.  After it dries a little while, say, ten minutes, you can remove the excess on the knob surface using a clean wooden toothpick.  If you angle the toothpick so it rides the edge of the groove, you can trim the white line just right, exactly at the top of the groove and it ends up looking perfect.

I glued the new spun inserts into the knobs using a silicone sealer/adhesive.  The new inserts are just slightly smaller than the indentation that receives them.  This kind of glue easily allows you to get them exactly centered.  I also glued the main tuning knob to the skirt by applying a few drops of super glue to the edge of the knob that fits into the groove in the skirt.

The chassis underside was somewhat dirty too – not nearly as bad as the top but some nicotine residue had worked its way down there over the years.  It was possible to do an effective job of cleaning, despite it being much more crowded with parts, by working Q-tips around things, lifting wires and harnesses and cleaning any accessible surface.

Remounting the escutcheon and dial assembly went according to the Collins service bulletin instructions.  The fiducial window went on fine.  I used a post-it note stuck to the front panel to prevent the plastic window from rubbing against the panel while being mounted.  The side of the window on which the red line is printed goes towards the inside of the radio.  I positioned the adjustment knob so that when the red line is vertical the knob’s setscrew is on the bottom and not visible.

Lining up the number dial with the white masking dial took some playing around, more than what is indicated in the Collins bulletin.  Simply lining up the center of a three-digit number as it instructs doesn’t work quite right.  I started with the 100 mark and went up and down from there to see if the numbers are centered.  Then I can loosen the idler gear enough to disengage it from the dial so I can make minor adjustments to the numbers dial.  Another minor difference is that when lining up the 0 point with the counterclockwise limit of the VFO, the tuning knob has trouble turning the dial around the stationary VFO shaft with just the setscrews loosened.  I had to help it along with my finger as I turned the knob.

In remounting the illumination bracket I noticed that there was still some yellowish discoloration of the metal that would not come off using Krud Kutter.  So I polished it off using Wenol.  But when using Wenol on aluminum it leaves behind a black oxide even after buffing – so I had to remove that with Q-tips and water.

A Heathkit nut-starter tool came in handy for reinstalling the nuts on the bracket mounting screws.

Reinstalling the S-meter was a bit tricky because the lower mounting screws are between the meter body and the chassis making it difficult to get the washers and nuts on.  I did it using tweezers for the washers and the nut starter to get the nuts on – then tightened them using a long ¼-inch socket extension with a screwdriver-type handle.  I only tightened these nuts enough to squash the lock washers flat.

The heterodyne oscillator crystals and the filters still had some yellowish residue, just like the illumination bracket.  This was a common theme – some metal surfaces came completely clean with KK (like the chassis) but others didn’t.  Using Wenol on the crystals made them nearly mirror-shiny.

Cabinet

The cabinet cleaned up well with a spray of KK followed by a rinse with water.  The inside front edges of the trim ring looked scratched from moving the chassis in and out, but they came completely clean.  It helped to use a toothbrush around the entire surface while the KK was wet.  Scuff marks on the top of the trim ring came off with automotive paint scratch remover, which also improved the look of the surface of the rest of the ring.

I put the receiver back together and tested it out – it still worked but I anticipate it being out of alignment due to my disturbing trimmers and other adjustments during cleaning.

The new, authentic, Collins reproduction feet I bought from Surplus Sales of Nebraska installed just like the real thing and look great.  You have to line up the front feet extenders properly so that the slanted surface is in the right orientation, tilting backwards.  I reinstalled the cabinet screws in the following order: feet, middle-rear bottom screw, two top front trim ring screws.


516F-2 Power Supply

The power supply chassis and cabinet were as dirty as the receiver, but somewhat easier to clean since there aren’t as many small parts mounted to the top.  It all came clean using KK and Q-tips.  The filter capacitors, although still good, look as old as they are and will be replaced.  The cabinet was in similar shape to the receiver cabinet and also had a blackish scuff mark around the entire leading edge of the trim ring.  It came right off during the KK soak with some scrubbing using a toothbrush.  I removed the speaker and grille before the soak, of course, and cleaned the back of the speaker with Q-tips.  I also removed the trim ring (which I did not do for the receiver) and washed it separately, since there seemed to be more dirt underneath it.  The nuts had been marked with the green clear lacquer inspection liquid and so when I replaced them I kept the orientation as original (for no particular reason).

I bought a complete set of capacitors – close to original values -from Mouser to replace C2, 3, 4, 5b (33uF 450V Xicon XAL), C5A (16uF 475V Vishay TVA), C6 (10uF 250V Xicon), C7 (10uF 160V Xicon), C1 (.047 1600V CDE metal polypropylene).


32S-3 Transmitter

The transmitter’s chassis was somewhat dirtier than the receiver’s, but its dial was whiter.  I wonder why...

I removed the tubes and tube shields.  I then removed the final cage lid and pulled the 6146’s.  The shield on the driver tube, inside the cage, was stuck onto the tube, probably due to the grime having been baked on.  So I proceeded to remove the cage itself.  The cage is fastened to the chassis with six self tapping screws from underneath.  A slot around the tune shaft enables it to be lifted up without removing the shaft.  But first I had to unmount the lid interlock (rather than unsoldering it) which has a wire that is the last remaining thing keeping the cage from being removed.  With the cage off I was able to remove the driver tube and shield together – but I’ll have to soak it to get the tube out of the shield.

The VOX control bracket is mounted to the front panel with two hex-shaped spacers with tapped ends to receive screws.  (Note that this is different from in the receiver, where the spacers are hollow tubes.)  These spacers are supposed to be tightly fastened to the bracket so that you can just remove the two black screws at the top of the escutcheon to remove the bracket.  But if the screws underneath the bracket aren’t tight enough, the escutcheon screws will turn the spacers and they’ll come off their inside screws instead.  It’s not a big problem but when it goes back I’ll make sure the inner screws are tight – they are hard to get at with a screwdriver while the bracket is in place.  This bracket also has the mount for the dial lamp, so making it easier to remove is a good idea.

With the control bracket off, I removed the dial using the same procedure (from the Collins service bulletin) as with the receiver.  I again cracked the fiducial marker window trying to get it off the center plastic hub.  I suspect that they become brittle after 40 years of heat, making it very difficult to remove from the hub.  It will still function fine but I’ll glue the cracked piece back in place after cleaning it.

I could not remove the slug rack as I did in the receiver because the power/function switch blocked one end of the clamp from being positioned between the front end of the rack and the front panel.  Even if I had a different clamp that would fit, this rack has a connector in the top that is wired into the rig and would have to be unsoldered to get the rack completely out.

The transmitter has many more pieces atop the chassis, and in some cases they are clustered in ways that make cleaning difficult.  Because of this, and because I couldn’t remove the rack, and since the rig was so dirty, I decided to use a modified version of W3ST’s soaking procedure instead of doing it all with Q-tips.  I sprayed most of the top surface of the chassis and components with KK and then rinsed with water using a pump bottle rather than a garden hose.  I then quickly dried everything using a hair dryer.  This worked amazingly well except for a couple of things.  First, even though I was careful around the serial number sticker, I still got too much KK on it and so the markings faded a bit.  Second, the spray/rinse procedure sometimes leaves a whitish residue, but only on certain parts such as the tube-socket metal rings and certain screw heads and control shafts.  This residue came off easily using Q-tips and water.  Sometimes just buffing with a dry Q-tip removed it.  I don’t know what this is but it seems to have a waxy, rather than a powdery consistency, which leads me to believe that it might be a bit of lubricant from certain mechanical parts that was carried away by the KK spray but didn’t come off with the water rinse that followed.

I didn’t spray the final amplifier components an additional time, so they’re not quite as clean as the rest of the chassis, which I did twice, but I didn’t want to remove the grease from the capacitor bearings.

During the spray/rinse process I was careful not to spray either the VFO or the control bracket, both of which I cleaned separately with Q-tips.  I also cleaned around the underside of the chassis the same way – as I did with the receiver.  Last of all I cleaned the front panel with KK and water using Q-tips.  The panel markings brightened up noticeably but aren’t quite as white as the bright white I use on the knob pointers.  This may be their original color but I don’t know.  If I look very closely at the markings I can notice that they have very tiny hairline cracks in the marking paint from age.  You can only see these under a magnifying glass or looking very closely at them.

I cleaned the cabinet, final cage, front panel pieces and dial in the same way as I did with the receiver, with some minor differences.  The knobs were all cleaned and their lines re-whitened as with the receiver.  Spun aluminum inserts were replaced too.  They all came out great, but the cabinet lid will require a bit of straightening near the hinge, where it’s bent just slightly, probably from someone putting something heavy on top of the rig.  The kHz dial did not come clean with only detergent in water as with the receiver.  I had to use Windex to get the clear areas clean and the white masking areas white again.  Thus I suspect that the grime on the transmitter had some different consistency than that on the receiver, although I can’t come up with a reason why that should occur, given the fact that the two traveled through life together.  All I can think of is that perhaps the transmitter didn’t get the constant direct blast of tobacco smoke, assuming the smoking operator was most often looking directly at the receiver when tuning around. Perhaps the inside of the transmitter was hotter on average and that made a difference in how things adhered to surfaces.

When reinstalling the dial, you come to the part in the Collins procedure where you have to align the numbers in the center of the white masks on the kHz dial.  I decided to try the other method suggested by the service bulletin – loosen the two setscrews in the VFO shaft and rotate the tuning knob until you get a good alignment.  This works great.  Evidently, the number of teeth by which the two dials differ is not precisely enough to keep the two in constant alignment.  As you rotate the dials with the tuning knob, watching the numbers in the dial window, you see the numbers move from one side to the other until they are completely out of sync with the white masks – that is, there is blank space centered in the window.  So by rotating the dials one way or the other, you can make slight corrections to the relative positions of the two dials.  Once you find it, the idea is to get that spot as close to the “100” mark (the center if the range) as possible.  That way, at “0” it’s only off a little in one direction and at “200” it’s only off the same amount in the opposite direction.  I think they must have designed it this way – clever folks, those Collins engineers!


Other interesting S/Line restoration sites:

Mark, K4SO has a nice set of pictures of his restoration of a Collins S1 line.  Also see his album on restoring a 30L-1 amplifier, and 312B-4 console.



Copyright © 2008 Christopher F. Codella, W2PA.  All rights reserved.