500ma78/79 blow up!

[harrybissell at prodigy.net]

Probably there is nothing in your circuit to limit the inrush current when the trannys in the 3046 are cold. The circuit will draw everyting it can get in that case.

Question: are you using the "servo" heat control (with temperature sensing done with one B-E junction)?

Q2: send me a copy of your schematic, I'll look...

The 78M may be saving you by going into current limit itself... Does it get hot (bet it does...) so you may be trying to pull several amps, and the 78M goes into thermal limit before the 3046 can self destruct...

Put an ampmeter in series with the supplies to the 3046... you should be able to read the current... The circuit should be limited to some lower value (maybe 100mA). More than that and you can fry...


 ---- On Jan 27 Ken MacBeth <macbeth2600 at yahoo.co.uk> wrote: 
> Hi, anyone got any why reason the heater elements in
> 3046 prodigy expo gens blow when basic 1 amp 78/
> 7912's are used as opposed to circuit specified 78m/
> 79m12's (500ma)are used, I've tried many times to
> solve this problem, and when I ask, I am normally told
> that the circuits should only drag the current they
> need...
> if any one out there is interested, check out my home
> built analogue site at
> http://www.macbethstudiosystems.freeserve.co.uk
> 
>  
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