Rick,

I *have* been hammering the poor little transistor used in the FET
driving circuit (base connected to the PIC), and yes this is the one
that blew. I must have been lucky that the original transistor must
have been 'a good un' as I didn't realise the mistake in adjusting
the trimpot for a good long time.

So thanks for that Rick; I'll replace the transistor with something
more rugged and look at adjusting the circuit *and leaving it*.

Having said that the circuit has been great for the last few years;
you wouldn't believe the number of batteries that have been brought
from (on a tester showing as) useless back to near original
performance. A friend of mine works in a garage here and has kept
all of us supplied with dead batteries that we now all use on solar
and wind power systems.

Rod

--- In randrdesulfatorforum@yahoogroups.com, Rick
<fun_4_me_now20012000@...> wrote:
>
> Hi Rod.
>
> --- "rod.badcock" <rod.badcock@...> wrote:
>
> > Sorry I haven't posted back on this forum sooner!
> >
> > To answer some questions: the 'amplitude' I was
> > referring to was the
> > pulser trimpot - as the coil audible oscillations
> > got louder I had
> > assumed amplitude.
>
> The trim pot is supposed to be set at build time and
> left alone. When you turn it you can operate the
> pulser WAY outside of it's specs. It is a wonder it
> didn't blow out sooner.
>
> >
> > With regards the fitted 2N3904 I was mystified that
> > after having
> > worked for years I'm only now getting a problem
> > (even when replaced
> > with 2N3904) and caused me to question if that was
> > all that was
> > going on.
>
> The one who's base goes directly to the pic through a
> resistor?
>
> That transistor gets hammered. If you crank up the
> pulser, you will excede it's max ave current and cook
> it.
>
> I suggest you replace it with something more rugged,
> and then set the pot to where it was when you bought
> the pulser. Richard Lines can help you with that.
>
> The next generation does not even have a pot. It is
> set by fixed resistors.
>
> I hope that helps.
>
> Rick.