British 'protection lamps' US equivalent?

[ricach]

I have a pair of Wharfedale Pro LA15 speakers that blew the fuses in the hi pass circuitry. There are no legible markings on the glass bulbs so I don't know what to replace them with. I've contacted support at the company - but oddly when they asked what country I'm from, USA, not a word since. Any subsequent emails go unanswered. Any ideas?

BTW: There are two bulbs soldered in parallel in the circuit. Not a very easy repair in the field.

[Steve Conner]

I'd be tempted to try a 12V, 10 or 20 watt halogen lamp.

[Alex R]

Tweeter protectors in PA speakers tend to be 24v 10w festoon bulbs, as supplied for truck and boat interior lights. Like this:

Festoon Bulb - Holt-r985

[Mark Black]

I believe the Wharfedales, like many other manufacturers including JBL, use an SK3 lamp. Specifications (and a great price if you want to order 400 of them) here: OS SK3/CWT/3 #35506(569 3"LDS) | OSRAM SYLVANIA | Incandescent

If you Google "SK3 Lamp" a few places to purchase in smaller quantities pop up.

Interestingly the 1156 (old school automotive "back-up-light") and 3156 (newer version of the same) lamps have the same voltage/amperage/wattage specs, so I suppose in a pinch and with some artful mounting (via silicone adhesive or some such) you could solder some wires to the terminals and get by for a while.

If I remember correctly some Peavey crossovers use what appears to be an 1156 lamp, though I think they grade them at the factory for a certain tolerance & resell them under their own part number. Most lamps are not inherently high-tolerance parts...

[ricach]

Tweeter protectors in PA speakers tend to be 24v 10w festoon bulbs, as supplied for truck and boat interior lights. Like this:

Festoon Bulb - Holt-r985

I would have to solder in a holder for a bulb like that, which is good, because the bulb thats in there now just has a wire coming out each end to be soldered into place. The horn driver is nothing I've seen used for a horn - it looks like a regular ceramic magnet used for normal speakers. But can't say I really spend much time dealing with speaker systems.

[Alex R]

Those SK3s look like the right thing. The festoon bulbs are pretty big, like an inch and a half or so, might not fit in.

[jrfrond]

You can get those dual fuse-type lamps from Parts-Express. Their part# is 290-659.

[J M Fahey]

As a reference, in up to 100/150W cabinets I use cheap, available everywhere 12V 15W car lamps , which means they are slightly over 1A current limiters (similar specs to what was suggested above).
Just scratch the side and solder them to the board. I always have some stiff 0.80 mm brass wire (the kind hippies use to make "jewelry") for such improvisations, also to hold boards "in the air", ground buss, you name it.

[ricach]

This is all pretty interesting since I had no idea it was so common to protect horn drivers and tweeters using 'light bulbs'. Why isn't a normal standard fuse used for this?

[Alex R]

Under overload the light bulb will glow, increase resistance and limit the current, whilst the fuse will just blow. Light bulbs allow the tweeter to keep tweetin'.

[Steve Conner]

That's it, take a beatin' and keep on tweetin'.

In some designs you can see the bulb shining through the bass reflex ports. I have seen an eerie pulsating glow come from inside speakers, either in the hands of an over-enthusiastic DJ, or at jam sessions that got a little out of control.

[Enzo]

And the bulb offers a more flexible protection, it is a variable resistance.


And frankly, fuses usually don;t act fast enough to save tweeters. They mainly offer the speaker owner mental comfort.

[J M Fahey]

Hi Ricach, forgot to ask, why do you ask for "british" bulbs?