Re: Circuit Symbol

Cursitor Doom <cd@notformail.com> wrote:

On Wed, 18 Dec 2024 16:30:57 -0800, john larkin <jl@glen--canyon.com>
wrote:
 

On Wed, 18 Dec 2024 23:55:14 +0000, Cursitor Doom <cd@notformail.com>
wrote:
>

On Wed, 18 Dec 2024 11:25:27 -0800, john larkin <jl@glen--canyon.com>
wrote:
>

On Wed, 18 Dec 2024 19:00:01 +0000, Cursitor Doom <cd@notformail.com>
wrote:
>

On Wed, 18 Dec 2024 10:57:10 -0800, john larkin <jl@glen--canyon.com>
wrote:
>

On Wed, 18 Dec 2024 18:38:55 +0000, Cursitor Doom <cd@notformail.com>
wrote:
>

Gentlemen,
>
A chum of mine who's into classic cars has asked me to take a look at
the radio out of his 1938 Bentley which has never worked in all the
years he's had it in his ownership. Obviously, given the year, this is
an all-valve job (if you're in the US, I'm referring to what YOU call
"tubes"). There isn't a single semiconductor in this thing cos they
weren't invented until much later. The valves require an anode
("plate" if you're in the US) voltage of 235V so there's a DC to DC
up-converter to generate that from the 12V battery. Rather interesting
approach they've used and one can see an embryonic SMPS in there!
Anyway, there's a schematic symbol I can't identify for sure. Could be
a fuse, could be a link or jumper, could be a current test point, I've
no idea. So can some kind, intelligent soul enlighten me? They're
labeled V1 through V8. Here's a pic:
>
https://disk.yandex.com/i/mIv_txLia6Xx4Q
>
TIA,
CD

>
Probably the tube filaments.
>
Incidentally, I have seen people selling solid-state plugin
replacements for vibrators.

>
Splendid suggestion, John. I must admit that never occurred to me.
I'm afraid this chap is a stickler for originality and wants
everything done with old parts. I did venture to suggest a modern,
monolithic converter but that was rebuffed most vociferously. Sigh...

>
I'd stick a transistor radio behind the old knobs.
>
It may have a dynamic speaker too, which could be hard to replace.
>
Buy the vibrator replacement and rub some dirt on it, or stuff it into
the ugly old can.

>
That's what I'd do if it were my car. You can get AM radios on 1/2"
square boards; just add your own L and variable C and a TDA2611A for
the audio. All sorted out. I told him I'd do it that way for free, but
if he wants to do it the hard way I can only offer guidance and
whatever vintage spares I have.

>
I recall that vibrators weren't reliable. Finding a replacement would
be tricky.

 
Simple enough to contrive a replacement using an old telephone
exchange relay if he'll accept that. It's miraculous they functioned
for as long as they did, given the hammering they took due to the way
they were wired.

The early designs were a bit unreliable but it was often due to contact
damage when the suppression capacitors failed.  Later designs were much
better engineered, with extremely ingenious mechanical arrangements to
minimise contact bounce and ensure that everything worked correctly at
the resonant frequency.

The later ones were surprisingly quiet, both mechanically and
electrically.  They carefully arranged the centres of mass of the
vibrating parts so that they didn't translate the vibations into
unwanted modes.

If the set was specifically designed to only work with a vibrator, the
rectifier could be omitted and a second set of synchronously-vibrating
contacts would do the rectification.  That more than made up for any
efficiency losses in the vibrator itself.


--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk