[R-390] Weird-ass PTO parts

[Barry]

> OK, I've been into the deep jungle of the PTO can and back out.
>
> I understand at least a little bit the oddball caps inside the
> can. I'm guessing that the big cylindrical one is some kind of
> fixed vacuum cap, and that many of the others have special
> tempcos.
>
> But... what's with some of the weird componentry outside the can
> but around the tube socket? As Barry was asking about, they've
> got a tiny glass piston cap in the plate circuit, although it's
> nominally detuned with a resistor to a very low Q. I associate
> glass piston trimmers with VHF/UHF high-Q (or at least "as higha
> of a Q as we can get") stuff, not with low-Q broadbandish type
> stuff.
>
> And then there's that bizarre waxed-up stack of ceramic bypass
> caps.
>
> Clearly really smart and experienced people, who understood
> lots of complicated mechanical AND electrical compensation stuff,
> made the PTO's. I'm not gonna try to second-guess what they put
> inside the can at all. BUT... the weird combination of stuff
> around the tube socket is just bizarre. Sort of like Gary Larson's
> "Cow Tools" cartoon
>
>  http://www.salon.com/people/portfolio/1999/12/21/larson/older4.html
>
> I'm left trying to figure out the deep meaning and purpose of
> these odd constructs. Any insights? (into either the PTO or cow tools,
> that is!)
>
> Tim.

One thing I do find a bit odd is the lead-length on the bypass capacitors in
that wax stack.  While the ground leads are certainly short enough, they
snake the "signal" end quite a way, at least for some of them.  I was
thinking if I rebuilt this, I would make these lead-lengths shorter;
however, like Tim says, I'm not in a position to second-guess why these guys
did things like they did.  They knew more about this than I'll ever hope to.

Barry - N4BUQ (who doesn't exactly "get" that particular Larson cartoon)