Substitution of the regulator transistor in early Bally/Stern high voltage power supplies


The following is mostly what I posted on rec.games.pinball on 18th. November 1999,but I have also included a couple of pictures. If you need to replace the 2N3584 in the +190 volt regulator,you might find this a useful modification.

I purchased a 1980 Bally "Space Invaders" and the first thing I did when I got it home was check the high voltage supply. Sure enough, it was 230 volts instead of 150-190volts. Of course the 2N3584 was shorted and the 2N3440's were blown.

I hunted around my local suppliers (I'm in Sydney,Australia) and only found one that sold the 2N3584......they wanted more than AUD$30 for it !!!!!! GASP !!!!! There had to be a cheaper substitute.

My solution was to use a BUX84 which has slightly higher ratings and only cost AUD$2.20. The BUX84 is in a TO-220 package instead of the obsolete TO-66 of the 2N3584. I'd guess the now disused TO-66 style would account for the high price.Manufacturers just don't use it any more.

The BUX 84 mounted on the existing upper hole of the heatsink and I drilled and filed the existing heatsink "base-emitter lead hole" to make sure there was plenty of clearance for the new transistor's base and emitter leads. The collector connection was made through the mounting bolt onto the case of the BUX84 and the collector lead (center one) was snipped off just out from the case because it was only getting in the way.

Cockroach view of the BUX84

To insulate the heatsink from the collector I used an insulating washer and pushed a close fitting piece of "spaghetti" tubing into the mounting bolt hole on the heatsink and cut it off flush both sides with a very sharp blade. The base and emitter leads fitted perfectly.

When replacing any components in these regulators it's essential to at least check all the transistors before switching on again because it's a direct coupled amplifier and when one component blows it usually takes out the rest like a chain reaction.

Full view of the modification (photos courtesy of Marco Rossignoli)

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