I recently picked up a very clean 312B-5 remote VFO and station control. The equipment performs well, however, the dial calibration is 6 Kc (how's that for a throwback) off from my KWM-2. It tracks perfectly so I'm guessing the dial has slipped the shaft. The manual says to "loosen the two set screws" and physically move the dial display. What set screws? Collins isn't the greatest on detials so I am guessing the set screws are on the dial shaft and not accessable from the front. I tried getting access to the front panel and dial assembly by removing the two top cabinet screws and the front feet, but only the right side of the front panel came free. Now what?
Am I on the right track? Where ARE those set screws?
It is very unusual that the dial has slipped on the 70K-2 PTO. Possible, of course, but, unless someone has loosened the set screws and has moved the dial, very unlikely.
First of all, does the dial indication "overlap" about the same amount on both ends of the dial. That is, can you turn the dial so that the frequency indicates about the same amount on the high end and low end (usually between 5 and 8 kHz). For example, the indication at the low end would be about 95 on the dial and at the high end 05 on the dial. Next, are the "end points" the same? That is, no matter what the actual frequency is at "0" on the dial is the frequency exactly 200 kHz higher at the high end of the dial?
If the overlap at both ends is approximately the same (about 95 and 205) I suspect that the coils in the 70K-2 have been "fooled with". I would set the PTO dial to 100 and adjust L-303 which is the coil that is located below the top of the PTO to zero-beat with the crystal calibrator in the KWM-2- unit. Then, check the the frequency at the "0" and "200" points. They should be pretty close. If not, then adjust L-302 which is the slug tuned coil on the top of the PTO until the end points are correct.
Now, if the dial stop indicates like "0" on the low end and "212" on the high end, then the dial probably has been loosened and then you will have to move the dial on the PTO shaft. There are 2-set screws on the hub of the dial located about 90-degrees apart. The set screws are NOT Allen head but are Bristol head (BIG difference). Loosen the first set screw and then rotate the dial to the next set screw. Remove the main tuning knob (again, the set screw in the knob is Bristol). Loosen the second set screw. You will notice that there is a hole in the front panel in line with the actual tuning shaft of the PTO. There is a screwdriver slot in the end of this shaft.
Put a screwdriver in the slot, preventing the shaft from turning. Using your other hand, move the dial to the correct frequency. Retighten the first set screw and then put the knob back on. Tune the PTO until the second set screw can be accessed and then retighten it. Depending on just where the set screws happen to be you might have to do the opposite. That is, hold the dial in place and turn the screwdriver until the frequency corresponds with the dial. You will probably have to switch between the internal PTO and external PTO several times to insure that the frequency ends up the same on both PTOs. Then retighten the set screws.
Technical Adviser Collins Collectors' Association
Wow, super response. Using the calibrator, if the KWM-2 reads 00 the 321B-5 reads 05, if the KWM-2 reads 200, the 12B-5 reads 204.5 (jeez these things track great!). I guess that points to a dial slippage. I tested the two top screws on the dial escutcheon and they are okay. There is only one screw under the dial (brass) but that's probably not "it."
Originally Posted by K9STH
I guess that means I need to figure out how to open the case then deal with the screws which sound very non-standard. Why does Collins do this to us? (BTW, I used to work for Collins at Newport Beach, CA).
Was I opening the ront case properly or is there a trick I'm missing to get the panel loose. Last thing I want to do is make things worse!
Thanks SO much for your advice.
You have to remove the 4 Phillips head machine screws on the front panel, the 2 Phillips head machine screws on the top, the 2 front feet, and the 2 machine screws that are towards the back on the bottom. Also, remove the wattmeter coupler.
The 2 set screws are behind the dial, down on the front of the PTO where the shaft from the variable inductor comes out.
Collins, Hallicrafters, and several other manufacturers used Bristol head set screws. Bristol head machine screws are very common on military radios because it is very difficult to "tear up" the heads when the proper wrench is used.
X'celite makes a very good set of Bristol wrenches. They are also available from Bristol as well as several other sources. Do a "Google" on Bristol wrenches and you will find quite a number.
Do you have the manual on the 312B-5? If not, you can download it from the Collins Collectors' Association website for free at
The manual for the 312B-4 / 312B-5 is about halfway down the list.
Thanks again. I will check out the Collins site.
This becomes more curious. My 312B-5 has no screws on the front panel other than those that secure the dial escutcheon. Nor does it have any set screws on the dial; it’s a push on affair. My KWM-2 has a round emblem while the 312B-5 has a “winged” emblem. I believe that means it came from an earlier model run or design.
You’re right about the Bristol wrenches, of course. I will get a set. I also agree that it makes no sense that the dial has mechanically slipped, but I can think of no other explanation.
Another challenge of this project is how to secure a PS-2 supply to the back of the KWM-2. I suspect finding that hardware is about like finding the Holy Grail.
I am confused!
None of the dials on the 312B-5 do not have set screws. Are you referring to the tuning knob on the unit as the "dial"? The dial is the round plastic on which the calibration (numbers) are printed and it is located behind the panel. Depending on the time frame when the unit was built, the some of the earlier versions do have a main tuning knob that "slips on". However, the majority of the main tuning knobs have a Bristol setscrew. The "winged emblem" is the mark of the earlier production runs of the 312B-5 and the "round emblem" is the mark of the later production runs. However, the "guts" are basically the same no matter what emblem is on the unit.
Be very careful when actually working on the dial (round portion with the numbers) because there is a nylon gear on the back of the front panel which drives the "mask" which causes the numbers on the dial itself to read the correct digits. The "mask" is concentrate with the dial itself and the speed of the "mask's" movement is different from the dial itself and that speed is regulated by the nylon gear.
Sorry for the confusion, Glen. The KNOBS on my 312B-5 do not have set screws. The Serial Number on the unit is 10363. I have attached a a pix to give you an idea of what I have.
All the 312B-4 and some of the 312B-5 units have 4-machine screws holding the panel. To remove the cabinet you usually have to remove the 2-machine screws on the top, towards the front and the 2-machine screws that hold the wattmeter pickup. Then remove the front feet and the 2-machine screws that are towards the back on the bottom. Sometimes, the actual unit comes out easier if you remove the trim ring.
You do need to be careful that you do not damage the cable that goes from the pickup to the meter switch.
Collins used "push on" main tuning knobs on the earlier 312B-5, earlier 32S-1 and 32S-2 transmitters, 75S-1 and 75S-2 receivers, and earlier KWM-2- series transceivers. Then, they went to the knobs with the Bristol setscrews. All of the later 75S-1 and 75S-2, 32S-1 and 32S-2, 75S-3- series receivers, 32S-3- series transmitters, the later KWM-2- series transceivers, and the later 312B-5 station control units had the setscrew knobs.
There was an optional weighted main tuning knob available for all of the S-Line equipment. That knob makes for a smoother "feel" as you change frequency. Those knobs are expensive. However, you can modify one of the non-weighted knobs by using buckshot, round lead bullets, etc., epoxied in the openings on the back of the knob. Although I do have Collins weighted knobs on all 3 of my S-Line receivers, I modified the knobs on the S-Line transmitters to make them smoother in operation.
Thanks again for your help. One last possibiity before I dig into the dial mechanism - I ran a three foot length of RG-58/U from the Kwm-2 VFO jack to the VFO jack on the 321B-5. Is this a critical length lead?
The length of the cable from the 312B-5 to the KWM-2 is not absolutely critical. Collins uses 48-inch lengths of RG58/U coax for almost everything. A 36-inch length of RG58/U should work fine.