S-100 power supply transformer

js at cimmeri.com js at cimmeri.com
Sun May 17 22:02:31 CDT 2009

Chuck Guzis wrote:
> On 17 May 2009 at 21:32, Steve Stutman wrote:
>> Consider that back in the 70s linear regs like LM309 and 7805 needed
>> fair overhead on the rail.
>> Newer LDOs by def need less.
> While I can understand that using a 78xx/79xx vintage regulator might 
> be important for the sake of accuracy, I'd be sort tempted to use 
> modern monolithic switching regulators if one wanted to preserve the 
> S100 "on board" regulation.
> No more "scorched PCB" or big honking heatsinks--and less conversion 
> of amps into heat.
> --Chuck
The problem with the onboard regulation is that many of those original 
regulators, though they might be working, are actually no longer any 
good.   Not sure if it's just age, or it's a lifetime of certain ones 
running too near max, but in all the ones I've replaced, I've cut the 
amperage draw of the board way down, sometimes in half.   

If they're going to be replaced *anyway*, then makes sense just to 
remove them and their associated, equally suspect tantalums/aecs 
altogether.    In my IMSAI, I feed each board power from a dedicated, 
pluggable line running to it... ground is still done through the connector.


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