Cylindrical. Axial leads.
Ordered caps for a speaker crossover because the leads had literally been shaken out of the originals. But I had no luck finding those bulbs. I would rather not jump it out. I guess I could and just put a beefier horn in it.
Possibly an automotive parts store, depending on what voltage rating was originally fitted. Some trailer lights use them. If it was not 12V or
24V then you'd have to look elsewhere.
I assume they are burnt out. You could try a 12 volt lamp with no more than
1-2 ohms cold resistance. You could also use a tweeter protector PTC resistor. I assume they were overdriven.Greg
Fuse lamp? It doesn't really have leads, but it's the same size as a
3AG fuse.Otherwise, maybe something like a 561, 563, or 211-2 automotive lamp. They have wire hoops on the ends. The 561 and 211-2 are 12.8 V, 0.97 A nominal; 563 is 13.5 V, 0.52 A nominal.
Do you still have a working lamp? If so, carefully put a few volts on it, measure the current, go up a volt, measure the current, etc, and pick something close to replace it.
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Matt Roberds
It's called a "barreter". It's just a lamp used as a current limiter.
The earliest reference I could find to baretter was from the pioneering days of wireless - apparently it was used as a detector.
The type I remember from the days of AC/DC TVs and radios was an iron wire filament enclosed in a hydrogen filled envelope.
The series chain of heaters had a very low cold resistance, so the baretter was included in series with any dropper resistor to reduce the surge current when switching on from cold.
In later equipment, NTC themistors became the norm, they reduce in resistance as current through them causes them to heat up, so they compensate for the low cold resistance of heaters.
The Polyfuse is a PTC thermistor; the resistance increases with temperature, at room temperature the resistance should be insignificant in the application, too much current causes heating and the Polyfuse has a sharp knee, so it cuts off current to the load till it cools again.
The thermistor types have significant recovery time - the PTC thermistor used to deliver a decaying burst of AC to the degauss coil in a CRT display had about 6 minute recovery time.
How big are they? We buy little incandescent bulbs from Mouser.
They might have others.. not the best search engine.
George H.
What did these tubes look like, any idea why they used iron and hydrogen?
They were long-ish tubes with an octal base. There was a glass stem inside with radial support spring struts and the wire zig-zagged up and down to complete a circle inside the tube.
When I got into the trade, they'd been largely superseded by rod type thermistors, there was just the odd one or two turned up in older gear - as they never gave me any problem, I never bothered researching it much.
Searching; "C1.pdf" will get you a datasheet, or search; "barretter" will get you some old radio museum pages for stuff they're used in.
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