Amplifone HV resistor mod

I never really liked the big extra resistors that Atari "designed"
into the HV-pcb. First of all, positioning them in an acaptable way is
pretty hard. I've seen some put upright and I've done some other
"creative" positioning, but whichever way you look at it, it's clumsy.

Apart from "looking bad" there was also something else that annoyed me
a lot more: They get pretty damn hot in use, and they are very close
to the (brand new) caps on the board. That means they're nicely aging
the caps right away again, something we don't want.

I had played with the idea to use some transistors instead of
resisitors. There are designs with 78xx and 79xx voltage regulators
that allow for more amps to be delivered using transistors and it
seemed like a more sensible way.
However, that would require some more modifications of the circuit on
the board which I didn't like. Also, Mark Spaeth pointed out that
transistor or resistor, the power was still going through either of
them and thus the heat would still be generated anyway.

So, next I thought about getting two wire-wound resistors that are
designed to handle some serious loads and have a metal "fan" body.
These are transferring heat a lot better than the ceramic one's. Now,
these baby's can be mounted on a heat-sink in the way like you do with
transistors and voltage regulators.

Since the heat-sink that is used by the 7824 and 7924 is not getting
hot at all, I figured it could handle a little extra heat from the
resistors.

Thus, I mounted the resistors on it. Had to drill some holes and I
used a thin film of thermal grease. There's no need to electrically
isolatie the resistors as the body is not in electrical contact with
the resistor itself. I ran some thick solid core wires through the
original resistor holes and soldered them as were the original one's.

There are some pics right here:
http://forum.arcadecontrols.com/index.php?topic=68094.msg1014797#msg1014797

André Huijts
andre.huijts@upcmail.nl

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Wed Sep 16 17:36:33 2009