R107 Receiver questions

[nirpvad]

Gradually moving along with my R107 restoration. Today, I took out the main tuning capacitor gang for cleaning and I find the the slo-mo drive is all gummed up with old grease and appears to be seized.

Has anyone pulled one of these to pieces and, if so, how is it done. I have removed the drive assembly and cleaned it externally which revealed 2 small countersunk screws on the periphery of the assembly as well as the 3 screws in each end.

The second question is in regard to the Crash Limiter. The diode block is missing from this set. I have an old Westinghouse rectifier block that was attached to the rear of the meter in an audio output meter. It's about 20mm in diameter and about 12mm thick. Would this work ok when rewired to the crash limiter configuration? If not, I could make one from 4 diodes - would 1A silicone diodes be ok or do I need to use something like 1N4148's. I can't see where it was originally mounted in the set but presume that it was probably wired directly to the Crash Limiter switch.

Cheers
Dave
VK4KDP

[G6Tanuki]

For noise-limiter diodes, you want something with low capacitance (to avoid the audio leaking through!).

Germanium point-contact diodes were the usual diodes-of-choice: OA81 or OA91 for example. If you're rich, try to get some "Gold bonded" ones [OA47 for example] as these are even better.

[RogerEvans]

I stripped and cleaned the tuning drive on a R107 just over 50 years ago so my memory is not very precise! I seem to think you remove the screws in the end plates and the interior mechanism 'slides' out (depending on how well the grease has set). It is a ball drive, not gears, I remember worrying that just using machine oil would make it slip but there was no problem and the rebuilt drive was beautifully smooth with minimal backlash.
On second thoughts, the screws on the front plate adjust the tension on the ball drive, so you might well need to undo the two countersunk screws as well. I daresay you will find someone with more recent experience!

Regards,

Roger

[nirpvad]

Many thanks, Roger.

I have taken out the 3 tension screws from each end and the two small screws but nothing seems to want to move - I guess it's all gummed up. I am having trouble removing the tapered pin holding the shaft adaptor on the rear end of the drive - maybe that has to come off before it will come apart. About to head over to a friend who has a range of pin punches.

Originally Posted by G6Tanuki

For noise-limiter diodes, you want something with low capacitance (to avoid the audio leaking through!).

Many thanks for the info - I will see what I can locate. I have some 1N34A's here that may work.

Cheers
Dave
VK4KDP