[ARC5] Transmitter capacitors

[AKLDGUY .]

Hi Brian

Interesting observations on the capacitors.

>Perhaps the bolt-on plates were there to provide alignment during
> rivetting and soldering?

That's a good theory. Perhaps the manufacturer assembled a large
volume of plates+two studs on a production line and kept them in stock
until required for pressing into the capacitors. Then there would be
only a single "lift, carry, and press" rather than lifting, carrying
and pressing each of the two studs and then fitting the plates. The
latter approach seems clumsy to me.

Production line assembly was one of the many jobs I've had. One of my
interests is trying to figure out how Aircraft Radio Corporation and
the other manufacturers could have assembled the sets the most speedy
and efficient way.

73 de Neil ZL1ANM


On 12/28/15, Brian <brianclarke01 at optusnet.com.au> wrote:
> Hello Roy and Neil,
>
> The studs are rivetted and soldered to the variable capacitors' side cheeks.
> The studs are stepped and the add-in plates appear to be jig-bored to mate
> very accurately with the stepped portion of the studs. Them's heavy duty!
> We will never know what was in Dr Drakes design notes, unless Gordon Eliot
> White captured them. So, whatever explanation we conceive will be mere
> hypothesis and conjecture.
> However, there are differences between the tuning capacitors for the VFO and
> RF PA:
>   a.. the VFO capacitor drive has captive ball thrust bearings at the front
> end of the worm drive shaft and a jeweller's bearing at the rear; these two
> need controlled spacing if there is to be neither binding nor bowing of the
> shaft-cum-cheek plate
>   b.. the PA tuning cap worm drive is tensioned only by a Belleville washer
>
>   c.. the VFO cap has a trimmable moving plate at the drive end – for tuning
> dial tracking?
>   d.. all moving plates of the PA cap are plain; during war, a 10% drop in
> power output through slightly misadjusted finals is far less important than
> being on frequency.
> From a logistics point of view, it would have been simpler to have all cheek
> plate drive shaft supports rivetted, soldered and then tin-plated in the
> same bath. Perhaps the bolt-on plates were there to provide alignment during
> rivetting and soldering?
> Dr Drake was excellent on design and prototype production - and hob-knobbing
> with the brass to win contracts - but he wasn't as smart on volume
> manufacturing for production as the Western Electric engineers. As the war
> progressed, I doubt there was much time for experimentation – that would all
> have taken place in the 1930s when Drake was solving the US Post’s problem
> of losing mail planes, and taking a punt on Edwin Armstrong’s
> superheterodyne principles, stolen by Sarnoff at RCA. I have not seen any
> examples of Dr Drake's very early Tx variable caps. What differences were
> there?
>
> 73 de Brian, VK2GCE.
>
> On Monday, December 28, 2015 2:34 PM, Neil said to Roy:
>
> Hi Roy
>
> Yes, I understand the requirement for stability, especially in the VFO cap.
> Something just occurred to me.
> Maybe the plates are not there to add rigidity. Maybe they're designed to
> expand and contract to the same extent and at the same rate as that side
> of the capacitor frame, so that the shafts don't bind in the studs. If the
> plates weren't there, extreme temperature changes from ground level to
> 20,000 feet would tend to result in bending of the capacitor frame and
> binding of the shafts.
>
> So my thinking is the opposite of rigidity. Deliberate expansion. If this
> is
> right, the shape of the plates is not simply random, they were made with
> great care, perhaps after lots of experimentation.
>
> 73 de Neil ZL1ANM


-- 

73 de Neil ZL1ANM