November
Why Can’t We Use the Wells-Gardner 6100 Transistor Upgrade Kit for the Electrohome GO8?
It’s an obvious question to ask: “You’ve already made a Transistor Upgrade Kit. Why can’t you just use it for the GO8, instead of making a whole new product?”
Both kits involve the burliest power transistors available today, mounted to a big, actively-cooled aluminum heatsink. But they’re implemented very differently.
1. The 6100 has three sets of power transistors: one for X deflection, one for Y deflection, and one serving as voltage regulators for the +-27V power rails. The GO8 has two sets of power transistors: one for X, one for Y, and no voltage regulation. So why don’t we just not use the third set? Read on.
2. The 6100 has a standard push-pull output section, with one PNP and one NPN power transistor. The GO8 has a less common push-push output section, with two NPN power transistors. (Unlike most NPN transistors, the 2N6259 doesn’t have a PNP equivalent.) Plugging one into the other’s output section would quickly cause a fire, much like this!
3. According to Sega/Gremlin’s manual, “The outputs of the X and Y deflection amps can swing between +60V and -60V. This voltage is high enough to provide up to 8 amps, peak to peak, of current through the deflection coils.” That’s 480 watts…more, if your wall power is greater than 110V (which nearly everyone’s is, these days.) There is not a single BJT power transistor available today that can handle 400+ watts…so we had to double up on the power transistors, which requires load-balancing resistors to avoid potential thermal runaway. In contrast, the 6100 runs at well under half the voltage (+-27V), and one set of 200 Watt transistors is sufficient.
4. 8 transistors don’t fit on the heatsink from the 6100 Transistor Upgrade Kit, so we had to have custom heatsinks fabricated! (Why couldn’t we just use two smaller ones? Two reasons. First, you can’t locate them such that the hot air from one blows into the other, and you can’t put them right next to each other or the manufacturer can’t assemble the PCB. Second, if you space them apart, the resulting PCB doesn’t fit in the GO8 chassis!)
5. The GO8 TUK fan is powered by 90VAC, while the 6100 TUK fan is powered by ~27VDC.
There are many more details…but this should help explan why two things that look mostly the same, and do mostly the same thing, are both very different and not interchangeable!