[David Dunlop]

Well it was an interesting weekend, lots of pluses for the most part, and fortunately, only one rather spectacular negative.

I was able to narrow down the possibilities for the poor performance of my Main Set Receiver to the 1st and 2nd IF Amp sections and Valve V1D in particular. The valve itself was in good working order, but one of the other components that should have been working well with it, was not.

So I took the receiver, along with my Remote Supply bits over to a friends on Sunday morning to take advantage of his far greater electronic expertise, and shop full of test equipment.

As I had suspected, the receiver was working very well both ahead of and behind the two IF Amp stages and we eventually worked our way towards the eight small trimmer capacitors set up in two banks of four in the pair of IF Coil Assemblies. This receiver, as in my Remote Receiver, has the upgraded Trimmer Capacitors that were issued 24 April 1959 for replacement of the originals.

These new capacitors were identified as:

CAPACITORS, Variable, air dielectric 7.5 to 99.0 uuf CT1B100 and came with a NATO Stock Number 5910-00-126-1583

I suspect they are a Hammarlund product and the ‘CT1B100’ might be their part number reference.

The original capacitors issued with the 52-Set were also very likely made by Hammarlund. They are described as:

CAPACITORS, Semi Fixed, 5 – 100 uuf, 10% ZA/CAN 4478

The first we attempted aligning, C7D, would not budge at all and we could see it had a coat of varnish on it, none of the other seven had showing. That should have been our first clue. Five of the remaining seven were almost spot on and needed little or no adjustment. The two others were off by quite a bit and things were sounding very promising as they were brought into alignment. That just left C7D, so we headed back to it.

With the second careful attempt at turning the inner adjusting shaft, it suddenly unfroze and started turning and things were sounding REALLY good! It was just coming up to its optimum alignment point when we heard a loud metallic ‘ping’ from inside the capacitor, the adjusting shaft parted company with the adjustment tool and bottomed out deep inside the outer support tube, and the small hex head collar that locks the shaft in position bounced onto the bench. Not good!

An inspection of the hex collar showed it was cracked right through one face and the crack had a lot of dirt in it, all the way through. Taking into consideration the air gaps between the fixed stator and adjustable rotator plates inside this capacitor are on the order of 1/64-inch wide, and the adjustable rotator shaft suddenly moved inward under its tension spring load a good 5/16-inch. I am pretty much assured this capacitor is now toast.

The two photos show the shaft settled deep inside the capacitor now and the crack through the hex collar.

I do have 8 of the original capacitors available from the Spare Parts Receiver and a quick look indicates they are probably all in good working order, but it would be nice to find an original upgrade version for the replacement project.

OF course Hammarlund went out of business in the late 1970’s, so another challenge ahead with the Main Set Receiver. Sigh!


David