chrise at pobox.com
Wed Jun 2 18:44:38 CDT 2010
On Wednesday (06/02/2010 at 07:10PM +0100), Tony Duell wrote:
> > Good suggestion Tim and thanks to others for their suggestions too.
> > I'll give this a try and see how it pans out. I can sure test the
> > theory with a VARIAC. The original transformer is rated at 7.25V @
> > 10A so I think the current capability is sufficient-- just too low of
> > a secondary voltage.
> If I had a penny for every time I 'thought it was sufficient/OK/not the
> fault/,,,' I would have no problem attending a VCF in the States :-)
> More seriously, I much prefer to make mesaurements and do tests before
> changing anything. That way you know what is going on, you know what the
> problem really is, and you can correct it. Not do something that seems to
> work now and whcih will cause problems later.
> Since in this case the first test is an easy one to do (namely measuring
> the AC voltage from the transformer secondary winding), I wouldn't even
> think of not doing it.
Yes Tony... I have done all of that. The secondary is dropping to nearly
6 VAC with only 5A load on the DC side of the bridge and 120VAC supplied
to the primary. The ripple on the DC side is in excess of 1V with that
same 5A load. I have swapped in alternative filter caps temporarily
and see little improvement. I checked the bridge for shorted diodes or
excessive loss and it looks OK.
I just received two new transformers to consider as a replacement for
the original. The problem with putting a booster on the primary of the
original is that it also raises the 24VAC secondary resulting in the +/-
12VDC rails going well above 16V. There's quite a few things in the
machine that use the 12V rails directly without regulators and I think
that's too high for some of them. So, I am going to put in a seperate
24VAC CT transformer for the +/- 12V supply and an 8VAC 10A transformer
for the +8V supply. This was a mod often done to the machine so I'm
not making it too much of a Frankenstein.
In restrospect, I think I am like you and will likely never sell this
machine... so, for now, it's about making it run right and having some
fun (again) with it.
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