We shall see. I have the set on my workbench now and can examine better.
My take that the pullies are different sizes is true, but for some reason
today the driver one seems to work better.

The height of the bumps is .050 to .057 inches.
The supposed height of the "3mm" drive belts is 0.048 inches.

I also noticed that the idlers were not rotating .. that introduces lots of friction.
Oil fixed it. I also noticed that the belt has to ride a bit too low in the idlers
so it was rubbing on the non-rotating part, where you can see a bit of wear.
This will need to be fixed.

I am designing a mechanism to add the third idler to adjust the angle
of wrap around the driver.

Progress, from an unlikely source. I went to Micheael's, the hobby store,
yesterday, to get an X-Acto knife. On the way out I noticed a display of
sewing stuff. Among the items was some "trim" stock which consisted
of some reflective disks attacked to tape. These were the proper size and pitch!

But they would not engage very stiffly. I tried it and it slipped on the dirver pully,
but not really badly. So I tried it driving just one dial, so it wrapped around the
driver pulley much more. It has sticky back so I just attached a piece into a loop
tape, which sticks well.

It actually works quite reliably. It can't last, of course, as its rather flimsy ..
but its says that the torque needed driving just one pulley is small. The problem may be
the extra torque needed to wrap it "backwards" over the two idlers.

The pulley I ordered is 1/4 inch wide. It will fit.Perhaps two shorter belts will work.

I posed a long piece yesterday but it didn't show up.

Short story: failure. I got the new 3mm pitch belts and pullies. I chose
one type randomly ... they are extremely similar.

I cut off half the cogs.

I installed. This turned out to be almost easy, not as bad as I expected,
except. That is, except for removing the main dials. It says "bend them",
as they run into the cams that adjust the pointers. They run into them badly.
I covered them with a thick sheet (say 10 mils) of sturdy plastic to protect them.
This was really needed as you have to bend them a dangerously lot. I was afraid
that they might break, but the came out totally unharmed.

And it almost worked. It didn't as designed, but I added two new idlers,
made of Nylon one inch in diameter and mounted where the screws near the driver
pulley are that hold the gearbox to the chassis. They make the belt contact 1/2 of
the driver pulley. These were obtained from Lowe's in the hardware department
cabinets for random junk (Hillman brand). That's a little secret trove for radio
repairers. I was afraid of losing the c-clips that hold the dials
on, but they had them! (I didn't lose them, however).

With the new idlers it almost does not slip. If I rotated the switch slowly with a
huge (15 inch) crescent wrench, so that it did not click into place, it worked.
But just using the knob, no matter how hard I tried, the "click into place"
resulted in slippage.

The next thing to try is to machine some rubber to the exact shape and
pitch of the old belt.

Thank you for your continuing work with this belt issue!

It confirms again why I much prefer the electronic side of restoration to the mechanical. A low torque drive belt application ought to be simple but your quest proves that it is anything but simple.

It reminds me of the early days of personal computers when I was in the doctoral program and working on a project involving LISREL with my dissertation chair and we needed the complete Greek letter set for a presentation program. I had some experience with Autocad and the work around was to digitize the characters into Autocad and use it rather than Xerox publisher to create the presentation. Had any of us had excellent handwriting we could have just penned them in on transparencies but that was beyond our limited artistic capability.

Rodger WQ9E

Rsingl: the problem is that it is HIGH torque. It gets high when it snaps into the detents.

I enquired with our machine shop foreman ... they can make anything, out of anything.
I once had a structure made out of the element vanadium! They have made things out of rubber.
But it has to be frozen! I'd have to use a commercial shop, which would not have
that experience.

So for the time being I am going to go with some sort of LED arrangement.

I installed LEDs just to illuminate the dials. See picture. This is 100% reversible:
it plugs into one lamp socket and is built on terminal strips mounted to
the screws holding the lamp holders.

Also another idea for belts: leather. I suspect that leather can be machined and for
sure it can be glued.

It is an interesting look that keeps your receiver functional.

Rodger WQ9E

I had a test leather belt made. Its promising.

The nice thing is that you do not have to take the set apart to install it:
It comes as a long strip that you glue together, which can be done inside the receiver.
You merely have to arrange bolts with hexheads so that you can move the idlers
with a small open end/12fold ring wrench.

I'm having a second iteration cut. If it works this will be good as these are readily made
by any lasar cutter.

They do smell truly awful as made, but it quickly goes away.

I had a prototype of a new object made today. This is a piece of
3/8 inch acrylic plastic that wraps the belt around more of the
driver pulley and also prevents the belt from slipping. It simply
can't slip: if it want to, it either prevent the slip or causes a jam. In my
quick tests it neither slipped nor jammed.

See photo

It looks like you are quickly zeroing in on a solution. Thank you for continuing to share information.

Rodger WQ9E

I got a second iteration on the leather belt made yesterday. This one fits properly
as made. Its working perfectly at the moment.

One concern I do have is what happens when the humidity changes. The answer
to that question will take 6 months wait until the wet months.

This proves that laser cutting is very viable. If only we could find reinforced rubber stock,
as that laser cuts nicely also.

I wonder if you could find an application for a typical reinforced v-belt the same circumference (or length) as your original and cut a .125 slice off to yield a suitable working stock ready for tooth machining? Or lacking that cut off a length .125 wide and stitch the ends together when finished?

I talked to Jim Jorgenson about his belts at Dayton many years ago and he said he based his original estimate for a run of 100 belts on probably not being able to sell all of those but soon realized he should have made more. He explained he had an engineering friend who worked for Dayco in Miamisburg at the time and the two worked together on the project to get it done.
I heard recently someone was trying to get some replacement belts produced again but I have not heard further about it. Interestingly enough someone else posted an unused Jim Jorgenson SX-88 belt on eBay a couple of years ago and it sold for over $700.00!

One could certainly cut v-belt material. The problem is that it would require cuts both ways.

i tried to pm this but couldnt. i dont have an '88 or have read much about them save they are rare and pricey and seem to have tuning drive problems. with all this cogged belt business i was curious if you had looked into miniature roller chain and sprockets as sold by mcmaster carr this stuff is incredibly small. ive no diagrams of the mechanism nor do i know what clearances you may have,i just thought i'd mention it.

I indeed have looked into roller chain. It can't be used without moving the location of idlers.
If metal it would short, if plastic it would get cut by the lugs of the front panel switches.

I have looked into changing the drive belt to currently available ones.

This is absolutely doable, as the belts and pullies are readily available: I actually have them.

What is not trivial it getting them in. The diameter of the shafts they go on in
not say 1/4 inch as they are the outer of concentric shafts, and like 3/4 inch diameter.
The present pullies would have to be machined off and the new pullies
machined to fit. I normally could do this myself, but our "student" shop is closed due to
Dictator Pritzker's orders. Roller chain would have identical problems in this area too.

As is my current leather belt works. I can't yet make ones generally available as it takes
far too much delicate hand work under a microscope to clean up the "suede" side. I wrote up
instructions, and realized this! This can be fixed with experimentation.

Oh yes! I got rid of lots more of the previously-reported warbles! Two things helped:
first making sure the receiver is held in the case only by the borttom two rack screws,
with spacers, and resting on the cabinet rails all the way at the back (not
screwed down to the cabinet rails. Second, moving the drive pulley away from
the front of the gear box ... it was rubbing intermittently. I am now very highly impressed
with the quality of this set.

tsubaki makes a series of chain rs11 and sells a range of setscrew sprocket's less than an inch. it seems their sprockets are metric sized at 6mm but a reamer could solve that. a nylon shoe might remove the slack. the stuff isnt cheap thats for sure,but any way i hope you figure it out.i wish i had a mechanism to play with ! how many of those did hallicrafter;s produce? it couldnt have been many. a fella tried to sell one on ebay a few months back and the starting bid was 3600$ if i remember right.

$3600 is in the ballpark. Its only a little too high. I paid somewhat less than that,
delivered to my door by the owner ... from California (I'm in Illinois).

But it had had the cabinet fully restored, to a perfect from a poor state.
Really perfect. The set itself was in good shape and unrestored.

Doug

as i was bored to tears i spent some hours trying to find any info on cogged,toothed or timing belts with a .250 pitch and it all came up, as you could predict, EMPTY. and that was in any tooth style or width. if there is any hope at all i would investigate sewing machines unless you've covered that as well. in particular vintage singers or even maybe english types. it does appear that people collect and restore them as well. my perusal didnt seem to get anywhere as belts all seem to be sourced by either part number or model number of machine not pitch.i can only imagine how aggravating this is. but i can say i learned a good deal more than wanted to know about belts!

I went through that same aggravating search trying to secure a spare for my belt when I acquired my SX-88 about 15 years ago and came up empty.

Also aggravating is those light masks should be so light and easy to move that it should take very little to properly drive them. My original belt is still intact and looks OK so I keep my fingers crossed. It spends most of its time on the 80 meter band but I haven't quite gotten so paranoid that I don't switch bands anymore

Rodger WQ9E

If your original belt slips but does not finally disintegrate, as mine did, it can be fixed.

Purchase some Barge original contact cement (with Toluene), in the yellow and red can.
Because the original belt is held together by nylon cloth, that can be glued with this cement
which is really strong. If a cog has broken off, buy some neoprene rubber sheet
of the right thickness and numerous X-acto #11 knife blades for your holder. With a
new blade for each, cut new cogs and glue them on before you reglue the nylon over them.
Then obtain from me (currently I have three) an acrylic piece (see photo) that
prevents the belt from slipping on the driver pulley and install it.

With patience these repairs can be done without removing the belt. You CAREFULLY
slide it behind the idlers, then slide the cogs off the pulleys, and this releases enough
tension to do the job, in sections.

If you are then careful to turn the knob smoothly and slowly, your belt will continue to
work a long time.