blown fuse indicator

[terminalgs]

Kind of gimmicky, but it might be useful to some of you.   With a single pilot lamp:  lamp works normally when fuse is intact. When the fuse blows, the  lamp flashes at an interval.  with these values, it flashes once time per second (roughly)





If you want the fuse between the wall and your switch, you can do something like this (but I don't think a single lamp can work as both an ON/normal lamp and an ON/blown-fuse lamp):





This is a Magnatone M20.  the neon is dedicated as a blown fuse indicator.  If you want it to flash, add a cap and resistor.


Here are a several articles or blurbs about using neons are blown fuse indicators in one pdf:


http://www.epanorama.net/sff/Misc/Meters-Indicators/Blown%20Fuse%20Indicators.pdf

[sluckey]

Thanks for that info. I think I can adapt this for my Leslie footswitch. I'm thinking steady for fast speed and blink for slow speed. I'm off to tinker. 

BTW, here's a pic of an indicator fuse holder that the military and FAA were fond of at one time...

[terminalgs]

If you don't have it already, this manual is a good one:


http://www.introni.it/pdf/GE%20Glow%20Lamp%20Manual.pdf

[Merlin]

Really, this is a bit dodgy. The main fuse is supposed to isolate the amp from the mains, totally, if it blows. This indicator defeats this total isolation. OK, it is high impedance, so in theory it does no harm. But if the extra components fail too...

Fuse indicators are OK for secondary fuses, but the main fuse ought to be respected. Don't use this idea in a commercial product, at any rate.

[sluckey]

I adapted the circuit from page two of your first pdf to my footswitch for my cheap Leslie assembly. Works great! The lamp blinks for slow speed and is steady for fast. Thanks again for sharing this.

[terminalgs]

that's a great  adaptation. 


I believe you need a resistor in series with the neon to serve as a ballast for the purpose of extending the bulbs life, and you don't really need the diodes.   you can do something like this:





playing with the values of the two R's and the C to set the two frequencies.

[terminalgs]

Really, this is a bit dodgy. The main fuse is supposed to isolate the amp from the mains, totally, if it blows. This indicator defeats this total isolation. OK, it is high impedance, so in theory it does no harm. But if the extra components fail too...

Fuse indicators are OK for secondary fuses, but the main fuse ought to be respected. Don't use this idea in a commercial product, at any rate.

yeah,   I admit I sleepishly post this thinking that the switch isn't ultimately  protected should the switch fail in some way that it actually shorts to chassis.   and it seems like a lot of extra components.  I suppose the ultimate safety fuse scenario would be two fuses (perhaps non-user servicable, inside the chassis), one on each lead from the mains, with those fuses rated at 4 or 5 amps.  all that out in front of this indicator and the user serviceable fuse, rated at whatever the actual circuit ought not exceed (1A).  Add a MOV in there as well.  the 4/5A fuses protect against dead-shorts in either the transformer or the switch (maybe not a timed fuse?). 


all of that seems like a lot of extra components.  again, kinda gimmicky, in this use.

[sluckey]

I believe you need a resistor in series with the neon...

There's a resistor built into the neon lamp base.

[terminalgs]

There's a resistor built into the neon lamp base.

Ah!  excellent! 

[PRR]

> you don't really need the diodes.

I *think* the diode is needed. It works by charging-up the cap. If fed AC, the cap charges and un-charges; with DC it is a classic neon oscillator.

Merlin has a point: even when the fuse is blown, there's power leakage. I'm not over-concerned. The blinky light calls attention to the fact "it isn't dead". The leakage in 1 Meg is actually legally "safe". It is unlikely to put much voltage through the transformer to the B+.

IAC, you ALWAYS Pull The Plug before you stick your hand inside.

One "surprise": with plug pulled there will be maybe 100 Volts stored on the neon's capacitor. Because of neon threshold and diode blocking, there is no bleeder path; and an effective bleeder would suck too much life out of the oscillations. 100V off 0.1uFd is probably not fatal, but could be a big surprise, make you jerk and fall and hit your head.

[terminalgs]

> you don't really need the diodes.

I *think* the diode is needed. It works by charging-up the cap. If fed AC, the cap charges and un-charges; with DC it is a classic neon oscillator.

ahh, I didn't think about that aspect of it., I bet you are right.