12V/15W Festoon Lamp Fuses

[nevetslab]

I just had a repair job on an Eden 410XLT Bass Cabinet, where one of the spring-clips that mount the 12V/15W Festoon Lamp Fuses had broken (Tweeter Fuse), and the client's attempt to use gaffer's tape to keep the lamp in contact with the broken end on the PCB assy didn't work. So, the tweeter was intermittent at best.

I had purchased a box of 10 pcs a few years ago, but wasn't able to find my receipt on that to see who I bought them from. Prices on those lamps range from $13 each down to under a dollar, I found, while searching for new supply, as the client wanted some spares. I did find an affordable source here:

https://www.bulbtown.com/211_2_F_T_3...se_p/42312.htm

10 pcs cost me $15.36 w/shpg



What I'm looking for now are replacement spring-loaded clips for these 8.5mm terminal ends. I had to resort to cutting an old Cliff phone jack apart, extracted the shaped contact for phone jack tip, and was able to somewhat reshape it close enough to serve as a contact spring to work with the one that didn't break off.

Anyone know a source for those spring clips to fit these lamp/fuses?

[xtian]

No leads for you, sorry. But, was it out of the question to switch to 0.25x1.25" or 5x20mm fuses?

[nevetslab]

NO. It was keeping with that same large automotive lamp that has somehow become an industry standard fuse mechanism for those cheap tweeters we find in bass cabinets for the past several decades. Not a common spring-clip. Or, at least I've never tasked myself to find a source for them.

[Helmholtz]

No leads for you, sorry. But, was it out of the question to switch to 0.25x1.25" or 5x20mm fuses?

It's not simply a fuse. Rather the soffit lamp acts as a compressor/limiter by PTC effect (similar to a bulb limiter).

[The Dude]

When I've run into this, I just use the leaded version of the lamp and solder it directly into the board. I think an auto parts store might have some sort of fixture you could rob the part from if you really wanted to provide a socket/clip.

[The Dude]

It's not simply a fuse. Rather the soffit lamp acts as a compressor/limiter by PTC effect (similar to a bulb limiter).

^^^^^^ Yes, exactly that. It's a fuse/PTC device all in one. IMO, it's actually a quite brilliant idea to use a lamp in this application.

[nevetslab]

I did find a JKL 2910F-42 Festoon Lamp Holder, which looks like a large bakelite Fuse Holder, but that's not what all the mfgrs of Bass Cabinets having these Festoon lamps fitted with riveted spring clips. This Eden cabinet is the first one I've come upon having a broken clip. So, it's not a common failure, but leaves ya sputtering your lip pondering what to do (buda-buda-buda-buda........)

JKL 2910F-42 Festoon Lamp Holder.pdf

[Helmholtz]

^^^^^^ Yes, exactly that. It's a fuse/PTC device all in one. IMO, it's actually a quite brilliant idea to use a lamp in this application.

Yes, it's a clever idea.
I first saw it used in PA speakers in the early 80s

[g1]

"Innovative CTL™ High Frequency Driver Protection"
That ctl stands for 'current to light' and Yorkville has a trademark for it (that name anyway).

[Helmholtz]

"Innovative CTL™ High Frequency Driver Protection"
That ctl stands for 'current to light' and Yorkville has a trademark for it (that name anyway).

As said that tweeter protection was used in German Zeck PA cabinets in the early 80s.

[g1]

As said that tweeter protection was used in German Zeck PA cabinets in the early 80s.

Yep. Lot's of brands used it, I bet it goes back even before the 80's. We just thought it was very funny in the shop when we found out what the 'CTL' stood for. And the idea that they trademarked it. It was the very same protection scheme others were using at the time, but I guess they thought it looked good in the sales brochures. Customers never thought to ask what the CTL stood for.

[Leo_Gnardo]

I think an auto parts store might have some sort of fixture you could rob the part from if you really wanted to provide a socket/clip.

True, I've scored fixtures and lamps from local auto parts shop. They were commonly used as interior lights in cars & trucks.

15 Mar 1992, at an outdoor concert in Augusta GA, the entire locally provided FOH PA system was Community cabs, with these built in limiter/fuse lamps. I'll never forget the day - beware the Ides of March. FOH mixer person had a heavy hand on the faders & set one side of the system on fire, later diagnosed to have started where heat from the limiter lamps set cab-covering fuzz alight inside several cabs. He told me some lady came up behind him screaming "your system's on fire!" to which he replied "Yeah, I noticed - and whaddaya want me to DO about it?" The show must go on.

Not long after a local club set up their house PA with medium size Community cabs. From time to time they were astounded when, during particularly loud honks from the band, the sound quit and instead bright light came pouring out from ports in the cab baffles. How baffling... at least they didn't set 'em on fire.

It's a good idea to make sure stray coming-unglued strips of cab carpet or anything else flammable can't come into contact with these limiter lamps.

[Helmholtz]

,.. the sound quit and instead bright light came pouring out from ports in the cab baffles.

I don't understand why the (tweeter) sound would quit.
When lamp brightness increases also the power delivered to tweeter must increase.

Like with any compressor/limiter there is an attack-release delay given by the heat-up time constant of the lamp (typically a fraction of a second).

[Leo_Gnardo]

I don't understand why the (tweeter) sound would quit.
When lamp brightness increases also the power delivered to tweeter must increase.

Like with any compressor/limiter there is an attack-release delay given by the heat-up time constant of the lamp (typically a fraction of a second).

In my experience, tungsten filaments have higher resistance as temp increases. Near-short when cold (room temp) and increase quite a bit as they start to glow red, yellow, white. Do I have it backwards??? Anything's possible.

In some Community speakers I have seen a bank of parallel lamps in series with the woofer/tweeter/crossover array. I've seen four paralleled inside some of them. Ram up the power and they get white hot, which explains what was happening at the local booze bistro. ALL the sound was attenuated not just the tweeters.

[Helmholtz]

In my experience, tungsten filaments have higher resistance as temp increases.

Yes, PTC effect.
As lamp and tweeter are wired in series, they share the same current. So when lamp current and power increases at large signal, also tweeter power must increase, though much less than without the lamp. Hence the compressor/limiter effect.

The lamp can't choke/mute the tweeter (except for a very short release time after a power spike) but limits tweeter current and power.