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If the bulb replaces the loudspeaker, i.e acts as a dummy load, then clearly the loudspeaker is protected
.Did you mean use the bulb as a dummy load, or use the bulb in series with the speaker to limit current?
Bear in mind that the bulb rating specifies wattage at the rated voltage when the bulb is hot. The bulb's cold resistance is a lot lower than its hot resistance.
You mean something you built yourself, or repaired, and question its proper function? I usually just measure to be sure there's no DC on the output (if applicable), then first hook the amp up to crappy low value speakers, actually just a loose driver I got out of something or other a long time ago.
Why would you want to put a bulb in place of a speaker?,
A 120v, 60w bulb is 240 Ohms....
Martin
A 120v, 60w bulb is 240 Ohms....
Martin
.... but maybe < 50 Ohms when cold.
True.
Martin
Yes as a dummy load. I was thinking a100w floodlight maybe. Just to protect the speakers from possible excess DC when
doing repairs. I have something like 80mv on one channel as DC offset, and the other is about 0v , doing the tests with
nothing attached to the spkr terminals. Its a Pioneer SX-240 Stereo and the protect relay keeps clicking out at about 33% volume.
There was alot of cracked solder on the spkr terminals, and one on the coil for the relay.
doing repairs. I have something like 80mv on one channel as DC offset, and the other is about 0v , doing the tests with
nothing attached to the spkr terminals. Its a Pioneer SX-240 Stereo and the protect relay keeps clicking out at about 33% volume.
There was alot of cracked solder on the spkr terminals, and one on the coil for the relay.
If the bulb replaces the loudspeaker, i.e acts as a dummy load, then clearly the loudspeaker is protected
Did you mean use the bulb as a dummy load, or use the bulb in series with the speaker to limit current?
Bear in mind that the bulb rating specifies wattage at the rated voltage when the bulb is hot. The bulb's cold resistance is a lot lower than its hot resistance.
Interesting idea. Maybe a spare electric stove coil would also do the same thing.
Good idea @Alec_t about the bulb in series with the speaker.
Good idea @Alec_t about the bulb in series with the speaker.
Keep in mind, that you can get a 50W to 100W resistor in the single-digit ohm value you want, for about $1 delivered on eBay.
Examples - https://www.ebay.com/sch/i.html?_from=R40&_nkw=50W+resistor&_sacat=0&_sop=15
Examples - https://www.ebay.com/sch/i.html?_from=R40&_nkw=50W+resistor&_sacat=0&_sop=15
If all you want to do is protect your speaker from excessive dc from the amplifier output then, connect a largish capacitor in series with the speaker. BTW, 80mv offset is not unreasonable but, if it increases during usage then there is something wrong. There could be something wrong with your offset detection circuit.
Offset detection circuits tend to be something like a window comparator (at least that's what I use). They have a largish value resistor on the input with an even larger capacitor connected from input to 0V to bypass the ac from the amp when it is up and running. If that cap' is below par, it could be causing your problem.
Probably more like 6 Ohms. A bulb filament when ON runs around 2000C, so a 0.5%/C tungsten tempco produces a 2000 x 0.005 = 10:1 increase in resistance hot vs cold.
True -- with clusters! Less because of the lower temperature, and less again because heating elements are typically made from wire (e.g. nichrome) with a much lower tempco (e.g., ppm/C vs ppk/C) than tungsten.
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