Quote:
Originally Posted by HamishBoxer
What a nice set.
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Yes, I think they did a pretty good job on it.
It also needed the usual mechanical things. For example the grease inside their gearbox had dried out so I removed the remains of it and replaced it. The regeneration control, on testing with a meter was intermittent so I pulled that apart and cleaned & lubricated it. Also a small drop of machine oil applied to the moving surfaces/bearings. And the inside of the main tuning knob with the rotating numbers also needed re-lubricating. Everything feels smooth now, but it will be a while before I can power and test it. I'm thinking it should probably slope detect an FM radio station, will be interesting to see.
For now, I have left the molded mica caps. They all test bang on for capacity and zero leakage on a low voltage test at least. So I will give them a chance to be saved, but, they are somewhat notorious for trouble.
I have attached the schematic. There is an 18 Meg resistor R9 in the grid of the superregeneration stage, that forward biases it, presumably when its oscillating the grid develops an average negative voltage with grid-cathode rectification. This resistor is open circuit or at least over 40 Meg, none of my meters can read any resistance at all. So I have ordered some, to make sure they are also vintage carbon composition types and do not have any troublesome inductive qualities.
I wonder what the quench frequencies will be on the different bands, but its probably very low compared to the received frequencies, maybe as low as 100kHz ? I can't wait to check on the scope when its working. There is nothing about this in the manual.