Dim bulb tester or limiter

[PelliX]

I bought some 100, 150, and 200W bulbs awhile ago. I had been mainly using the 150. I hope the batch I got lasts me a long time. I fear incandescents soon will be worse than vacuum tubes as far as availability.

[edit: looks like they’re still available on Amazon.]

They're still being produced in large quantities, though with vast geographic areas outlawing them for 'regular domestic' purposes the prices are likely to go up a bit. Don't forget that apart from the EU and to a degree the US and Canada they're still the de facto standard that they were here. LED will slowly replace some parts of that, but cheap LED's currently simply don't provide the same amount of practical light (also relating to the colour spectrum they emit) at the same price, so the key functionality is lacking without investing more - which we all know is not the average consumer's strong point.

I suppose, technically, if you needed a 150W but couldn't get it, two 75W's in parallel should do the trick...

The only 100 watt bulb I found i a specialty bulb dont Laugh it looks like a mad scientist !

I like it, haha! I have a couple of those, too, though with 'regular' E27 fittings. Even the one I harvested from an ancient PAR64 had the E27.

 

[Phoenix1]

Hey Gentlemen there in the UK I have a friend that says he can get incandescent light bulbs there for me but needs to know what size the threads are UK style ?
thanks for the input ! I measured with my calipers and they seem to be a 26mm.

 

[Purgasound]

Why such a high wattage?
As a ‘special’ for use with a SVT, yes, they’re handy.
But for general purpose use it’s not going to provide much of a limit on current flow, and the instantaneous initial current peak could be enormous.
Such a high wattage could allow common newbie errors eg reversed ecaps / diodes to still result in things being damaged, even if it’s only a fuse.
I suggest to have a range of bulb wattages available, start as low as is feasible for the application, and work up.

I think it may have been me that put the ‘bulb wattage twice amp wattage’ guideline out there. It should workout ok for most typical class AB amps.

Any bulb used in a LBL will have an easy life, I’ve never had one fail on me.

I’ve got a variac but pretty much only ever use it to tweak mains voltage to 240V.



Surely that’s wall outlet then variac then LBL then ‘equipment under test’?

Thanks for the tip. I should keep more on hand anyway.
When I built mine I started with a high wattage bulb as I was working on a Mesa 400 bass amp that was driving me crazy. I chased down problem after problem. Fix one thing, find something else wrong... It ended up being a conductive board that cascaded into a mountain of failures. No fun on that one. Then I just left it in there since I worked on a bunch of SVT's as well.

 

[TomCarlos]

I did not see anyone post a circuit for the bulb limiter. So here it is.

I built a simple bulb limiter and then a combination Isolation Transformer, Bulb Limiter with a lamp bypass switch. I will typically connect this to my Variac. Once I know the amp is not pulling excessive current, I can disconnect these items and plug the amp directly to the wall outlet.

 

[PelliX]

Hey Gentlemen there in the UK I have a friend that says he can get incandescent light bulbs there for me but needs to know what size the threads are UK style ?
thanks for the input ! I measured with my calipers and they seem to be a 26mm.

The two common types are E14 and E27. E27 is by far the more common and the type you probably want for this. The names actually refer to the diameter of the thread; 14 and 27mm respectively.

 

[jgab]

So a 100 watt bulb ok for a LBL when working on a 100 watt amp, or 200 w bulb in LBL?

 

[Sigs]

So for UK, what gauges of wire is used for 2 core and 3 core cable, and what is the recommended fuse rating ?

 

[Pete Farrington]

0.5mm2 is fine, 0.75mm2 cable is a bit more physically robust.
What do you envisage using 2 core for?

 

[Helmholtz]

I suppose, technically, if you needed a 150W but couldn't get it, two 75W's in series should do the trick...

To replace a 150W bulb, the two 75W bulbs need to be wired in parallel.

 

[Helmholtz]

A well chosen bulb limiter is superiior to a variac as it limits both current and voltage.
Using both is overkill and can cause confusion.
It is essential to get a "feeling" for the light level.
In any case the amp chassis must have a good connection to installation safety ground.

 

[Sigs]

0.5mm2 is fine, 0.75mm2 cable is a bit more physically robust.
What do you envisage using 2 core for?

To build a dim build limiter as per this video, it uses 2 core from the bulb to the socket.

 

[PelliX]

To replace a 150W bulb, the two 75W bulbs need to be wired in parallel.

Yes, uhm, lemme fix that.

Using both is overkill and can cause confusion.

I often run variac -> LBL with a bypass option for both. I did confuse myself once, I'll admit, hehe!