Overload indicator..how does it work ?

9/25/2013 12:17:32 AMVianney

Hi to all,

Since i'm restoring old radios, it's the first time i see an overload indicator in my sets.

It's on a Marconi #71

It look like an ordinary 6.3v bulb.
But i'm not sure what kind of bulb i should install ?

It's connected directly to the voice coil.

Anybody have seen this before ?
How does it work ?
Does this could affect the audio output volume ?

Thanks
Vianney

9/25/2013 12:20:38 AMVianney

here is the picture

9/25/2013 12:53:42 AMCV

Uses a property of an incandescent lamp: when a lamp is cold (not enough current through it to light it) the filament resistance is very low- tenths of an ohm. When enough current flows through it to heat the filament up (causing the bulb to light up), the filament resistance rises rapidly and therefore drops the current through it proportionately.

9/25/2013 7:05:40 AMLewis

:Uses a property of an incandescent lamp: when a lamp is cold (not enough current through it to light it) the filament resistance is very low- tenths of an ohm. When enough current flows through it to heat the filament up (causing the bulb to light up), the filament resistance rises rapidly and therefore drops the current through it proportionately.

I used to work for AT&T, and we used bulbs as varible resistors in some circuits, like when picking up a phone would short out the 105 Volt ringing circuit. Quite often, you would see a bank of bulbs, some flashing at 20 Hz., absorbing the short that would otherwise blow a fuse.
Lewis
:

9/25/2013 12:32:13 PMCV

Believe it or not, we used them in the avionics industry, too. They went into a military product that was subject to having its (fairly powerful)audio output ports short-circuited by greenie tech soldiers. Small light bulbs (covered in black heat shrink) were hardwired right onto the driver circuit cards to mitigate the overload should a short be inflicted on the output.

I doubt that this would have been acceptable for commercial avionics gear, even back then (mid-1970s)- but the mil customer (USAF) was willing to put up with some "innovative" designs as long as they could (figuratively) stand up to some soldier-technician who preferred to take things apart with a hammer instead of a wrench.

9/28/2013 8:51:47 AMLewis

:Believe it or not, we used them in the avionics industry, too. They went into a military product that was subject to having its (fairly powerful)audio output ports short-circuited by greenie tech soldiers. Small light bulbs (covered in black heat shrink) were hardwired right onto the driver circuit cards to mitigate the overload should a short be inflicted on the output.
:
:I doubt that this would have been acceptable for commercial avionics gear, even back then (mid-1970s)- but the mil customer (USAF) was willing to put up with some "innovative" designs as long as they could (figuratively) stand up to some soldier-technician who preferred to take things apart with a hammer instead of a wrench.

Hey, I quit AT&T to do avionics work at Delta for about 35 years until retirement. The biggest problem we had with ex military was the marines. They are traiined to kill people and break things. (;>))

Lewis
:

9/25/2013 4:14:34 PMRichard Dale Brown

:here is the picture
:
:

:

Looks to absorb some of the audio at low level input but will protect the speaker coil if level gets too high
by having the higher wattage just light the bulb instead of burning out the speaker coil. Hickok tube testers us this principle as a overload fuse on their tube testers. RDB

9/25/2013 6:15:29 PMRichard Dale Brown

:here is the picture
:
:

:
By the way I would like to know the procedure of sending a schematic on this site, I don't see any send attachment send button.

9/25/2013 7:53:18 PMvianney

There is no attachment send button.

If you put the mouse arrow on names, you can see email address.

Simply use the email address to send schematics.

Or include an "IMG SRC link" in your body text.

Vianney

:By the way I would like to know the procedure of sending a schematic on this site, I don't see any send attachment send button.
:

9/28/2013 4:23:51 PM*** Edd ***

Sir Vianney . . . .

Quote:

There is no attachment send button.

If you put the mouse arrow on names, you can see email address.

Simply use the email address to send schematics.

Or include an "IMG SRC link" in your body text.

Vianney

:By the way I would like to know the procedure of sending a schematic on this site, I don't see any send attachment send button.

:

Unquote:

I see that you repeated your earlier query on the VERY last statement above . . . . . . . so, let me further Edd-i-cate you on the proper HTML protocol coding for your then being able to accomplish your image posting on this site.

I will be using the examples repeated twice, on the first one I will purposefully introduce a HTML error in order to permit the WHOLE text to be shown on the page, but with your picture (schema) not showing up properly by virtue of that erroneous posting error.

On each of the text examples below, my introduced HTML " error " is being accomplished by the use of conventional left and right brackets [ and ] INSTEAD of the actually REQUIRED,
(HTML sensitive) < and >
brackets.

Thereby, you will then be able to read my each and every keystroke, since that info will NOT validate and thereby, stay and be visible on the page for you to see.

Then, if you want to try it out, just sub in a HTML correct < or > instead of my initial [ or ].

S o o o o o o . . . Here goes:

I see with your very first posts display of a RED x in a box, that your image info was NOT being accepted.

Thereby, its giving you that error message.

I then tracked down that images origin and found it as having its URL addee as being :

http://imageshack.us/a/img845/4243/j3qb.png

Therefore I needed to HTML prep it up by using a . . .

Simple header of:

[IMG SRC=

And an even shorter tailer of:

]

Or, with it all being put together as:

[IMG SRC=http://imageshack.us/a/img845/4243/j3qb.png]

On the line just above, my introduced errors permitted you to STILL be able to see the typed in procedure, so now I'm going to use the required < and > in order to get a valid image below.

Here goes . . . .brace yourself ! . . . . .

and . . . .BAM M M M M M . . . . . there that desired image is

And BTW that lamp is shunting the speaker and is voltage and current selected such that as the power drive to the speaker is increased, it starts stealing some of the power from the speaker at higher levels and peaks.

So now, while we are on a roll . . . . . Lets look at your magnificent rework of ONE grungeeeee old Philco? coil . . . . so much so, that you probably couldn't even see under the wax for the eating away of a pinpoint of the copper wire and its resultant blue/green copper sulfate residue.

Its demo is initially erroneosly prepped up as being :

[IMG SRC=http://imageshack.us/a/img607/6081/rfcoil.jpg]

And when we amend it with the CORRECT usage of < and > we then come out as :

Proceeding further, there was your
"Macaroni" restoration with its dial
and its solid state yellow-green- red LED conversion.

It was initially being written up as:

[IMG SRC=http://imageshack.us/a/img94/4357/bargrapho.jpg]

Then, rewritten correctly, and and validated as :

I didn't hiccup the camera shutter . . . . did you ?

This was its circuit being used, and was initially written up as:

[IMG SRC=http://imageshack.us/a/img38/736/ba6124vumeter.png]

Then being rewritten correctly and coming back validated with this picture :

And then there is that very DISTINCTIVE lighted Lucite dial scale treatment on this special radio of yours:

Initially written up to show you as :

[IMG SRC=http://imageshack.us/a/img193/3821/dial.png]

Then finalized correctly with this pic of :

And fina l l l l l l l y . . . no cats were harmed by this posting . . . but your cats neck CERTAINLY came close to being painfully sprained !

This pics initial write up was:

[IMG SRC=
http://imageshack.us/a/img838/2747/chattg.jpg]

Then, its come back, after its HTML error correction was :

http://imageshack.us/a/img838/2747/chattg.jpg>

Thasssssit . . . . . .

73's de Edd

I used to think I was indecisive . . . . . but now . . . . . I'm not so sure.

:There is no attachment send button.
:
:If you put the mouse arrow on names, you can see email address.
:
:Simply use the email address to send schematics.
:
:Or include an "IMG SRC link" in your body text.
:
:Vianney
:
::By the way I would like to know the procedure of sending a schematic on this site, I don't see any send attachment send button.
::
:
:

9/28/2013 4:35:11 PMThe RED X