Will no output devie hurt output transistors?

You are either going to have to call the alarm manufacturer, or find the original owners manual.

Many (not all) alarms, however, will default to 1234# if there is a power failure long enough to drain the battery, and whatever process holds the memory. This is a slim-to-none chance, but probably worth taking.

Our ADT system defaulted this way after about 2 years of downtime. We switched systems as ADT wanted an obscene monthly fee and a very long contract.

Peter Wieck Melrose Park, PA

Thanks for the reply pf, but I'm still interested in the questions.

Years ago, I was told not to play my stereo with no speakers, for fear of somethun' or other. Of course that was 1968, a good year for audio.

Is this still an issue with current electronics, like audio amplifiers and burglar alarm amplifiers?

So if I take the fuse out of the circuit to the sirens, but the siren driver is still functioning, do I risk burning it out? Even if it's like this for say, 20 hours? Or can it go like this with no harm to itself?

(These 3 questions are still important regardless of whether I disconnect the siren driver from the control board.)

But.. what if I disconnect the siren driver from the control panel (which I did)? They're separate boards. Do I risk burning out the output of the alarm control panel, if say it is run. again, 20 hours? Or can it go like this with no harm to itself?

That was only ever a problem with tube (valve) designs. No load could cause the output voltage to rise enough to damage some components. I am not aware of any modern equipment with similar restrictions. When transistor outputs arrives to replace tubes, that was one of the big advantages. You didn't want to short the outputs, but having them open was no problem at all.

That is only partly true. Solid state amps that have output transformers or chokes are also vulnerable. In fact Delco car radios had a warning sticker on them that read "DO NOT OPERATE WITHOUT LOAD". Those were a class A open ended stage simply running into an inductor, but it did produce more power than the SESAPP at a given voltage. It was actually capable of almost nine wattts nto eight ohms but they didn''t bias them hard enough to hit that l evel without distortion.

Any amp that uses an outpur transformer or choke can be damaged if operated without a load. The old tube stuff, what was actually the problem there wa s the tube sockets themselves because of the unbridled inductive kick when they got clipped with no load.

I've been in the argument about tubes and don't want to dwell on it, but on e thing to remember is that a triode is still a diod, a tetrode is still a diode. When you get to a pentode maybe not so much because of the suppresso r grid, but most of the other ones simply do not conduct in reverse. Genera lly the output devices and transformers could handle the voltage, what happ ened alot was that the tube sockets arced over.

The failure mode is different in a solid state unit. The inductive kick cau ses forward current to flow in the collector to base junction and the trans istor really does not like that.

From what I've read a bit more recently, because there are still tube amps around, especially for guitars and these high MFs might forget to plug in t he speaker, (oh, I got tons of stories about musicians, I mean, nice guys u sually but electroncs is like speaking Martian to some of them) now some de signs include a diode to ground from the plates of the output tubes. This l imits, actually damps, the inductive kick in case a speaker is not connecte d. However one tech around here reported that he had some problems adding s uch diodes to an existing design, and I never got the full details on that. It's just not something I have explored and queried about.

Anyway, getting to the OP here, the main thing is simply to look at the uni t and see if it uses an output transformer or choke. If not, most solid sta te equipment can run full blast for decades into no load. However, not know ing the impedance of the guy's siren or whatever, there might be a step up transformer to drive it. Actually that would tend to be less susceptable to such damage than an output circuit that steps down.

When they got to OTL (output transformerless) SESAPP (series arranged, sing le ended push pull) circuitry the danger was pretty much gone unless the de sign itself was defective. Or people. I remember working on a Harmon Kardon Citation 12 and people said you could use 2N3055 for outputs. NOPE. The vo ltage Vcb is not high enough. Now in THAT case because the load is not pull ing down the power supploy rails there might be a prblem, especially iif yo u have transistors that are margnal. Those ratings on the spec sheets are M INIMUM, or WORST CASE. Personally I just use 2N3773s in something like that , which have a nice smooth gain curve as well.

Bottom line, most stuff doesn't care if there is a load. Exceptions are far and few between unless you deal with old stuff or tube stuff. This is supp osedly an alarm system, and those barely existed in 1963 when this could be an issue.

Yea, big tube amps should not be run at high volume for any length of time with no load (speakers or resistors) connected. But this was not really true for small amps. like and old tube table radio, portable record player, etc. I never had any problems running that small stuff without a speaker. For power amps, guitar amps, PA systems or high powerred stereos, I had a pair of 8 Ohm 100W wirewound resistors to place across the spkr terminals.

I am not sure if I agree about the no need for speakers on the EARLY solid state devices. Sure you could run a pocket transistor radio with no load, and it would be fine, but I was told to NEVER run those early power amps without a load, and told that they would fry the output transistors a lot faster than a tube amp would be harmed.

Just because I was told this, does not make it true. That was in the early 1970s, and most of my information was from magazines (like Popular Electronics), or word of mouth from employees or other customers I ran across at electronics parts stores.

I have heard that modern solid state devices are safe to run without a load, but I dont think I'd try it for any length of time on anything that outputs more than 5W. Particulary if there is an input source.

To be safe, go on ebay and buy a suitable resistor. I just looked and you can buy a 8 ohm 100W wirewound resistor for as little as $3. For $3, why take a chance, esp if you plan to run it for 20 hours. And that resistor can be used in the future for all sorts of repairs on almost all power amps, except those rated over 100W. (Which you wont likely encounter).

• Ebay has an 8 ohm 1000W resistor too, for . Thats one huge resistor.

• If you cant get an 8 ohmer, a 10 ohm will work too. Just make sure the wattage can handle what you are working with.

(I have no clue what the wattage would be on an alarm system) ????