07-01-2020, 02:42 PM
So I thought I’d throw in my 2 cents on that brass strap cap on the tuning cap. And after 3 years of not restoring anything, I got ambitious and pulled out my junk model 70 – an early build ser. no: A72252. Sure enough, it has the strap. That strap is permanently adding maybe about 30 pf to the cradle plates of that section. Which means that section will track about 30 pf above the other 2 sections.
But then I see that the copper adjustment cap. plate for that section is shorter, smaller than the copper plates for the other 2 sections. So the short copper plate is adding less capacitance to that section than the other 2 copper plates add theirs.
I’m just guessing that the strap is making up for the difference between that shorter copper plate and the other 2 longer ones. In other words, the strap just adds back what the shorter plate takes away. Seems like adding that strap is an odd thing. Speculating even further, maybe during manufacturing they had some shorter copper plates for some reason. Error? Maybe from another model? I note that later 70s don’t have that strap and also have all the copper adjustment plates the same size. Again, just my 2 cents.
Vic
But then I see that the copper adjustment cap. plate for that section is shorter, smaller than the copper plates for the other 2 sections. So the short copper plate is adding less capacitance to that section than the other 2 copper plates add theirs.
I’m just guessing that the strap is making up for the difference between that shorter copper plate and the other 2 longer ones. In other words, the strap just adds back what the shorter plate takes away. Seems like adding that strap is an odd thing. Speculating even further, maybe during manufacturing they had some shorter copper plates for some reason. Error? Maybe from another model? I note that later 70s don’t have that strap and also have all the copper adjustment plates the same size. Again, just my 2 cents.
Vic
