SparcBook Tadpole

Tony Duell ard at p850ug1.demon.co.uk
Thu Aug 12 14:22:55 CDT 2010


> But that describes everything we talk about here that uses magtape, disk pa=
> cks, 7400-series TTL, ASICs, (god help us) ECL, et tedious cetera.  Yes, in=

True enough :-(

>  another few years my Voyager will have a dead NVRAM again and I may or may=
>  not be able to get another chip.  I might not even be able to get a new 
> battery: that's a problem with my Minolta SRT series SLRs, where the 

I think that's unlikey. The voltage is not too critical (it needs to be 
between 3-ish ance 5V, I think). I have had success using a couple of AA 
cells in series (normal 1.5V Duracells) as a replaemeent for a backup 
coil cell in some systems. No, they don't last as long (shelf life is 
lower), but they are avaialble _anywhere_.

> excellent TTL metering doesn't work anymore because it was designed to 
> be powered by mercury cells that I can't buy anymore. 


While you can, alas, no longer get mercury batteries, there are plenty of 
work-arounds for this. If the STT101 I've just picked up from my pile of 
odd cameras is anythign to go by, it takes a single PX13/PX625 cell. 
There is an alkaline equivelent that's the same size, but highter 
voltage, and I susepct, alas, the Mimnolta meter woudl care about that. 
Often connecting a single shottky diode in sereis with the cell will do 
the teick, if there's space inside the camera (sorry, I've not pulled the 
bottm plate to check), then it's easy to add it. If there isn't space, 
then there's a fairly expensive adapterwhich takes a smaller alkanline 
cell and includes a series diode. Or you could make soemthing like that. 
Or a new battrey cover containing contacts with wires leading to an 
external PSU of the right voltage. 

If you like, I can take my SRT101 apart and see how the metering system 
works..

FWIW, I'v;e never found a classic camera/exposure meter that will be 
damed by using the alkaline rather than the mercury cell. It may give 
silly readings though. It's worth trying and comparing with a known-good 
exposure meter.

Some cameras used bridge circuits for the meters. East German Prakticas 
did. As dod at least one of the metering prisms for the Exakta. if the 
correct exposure is indicated by the bridge being balanced, then the 
battery voltage is irrelevant (within reason), so you cna use the 1.5V 
alklaline cell in your MRL3 or whatever without problems

The Pentax Spotmatic is a ridiculous design. it's a bridge alright, but 
the correct exposoure is indicated by a small current floing through the 
meter, the bridge is not balanced. The official rason for this is that 
you can't get an 'correct exposure' indication if the battery is totally 
flat (so the meter can't deflect at all). FOO!. It would be extremely 
rare that the controls were set just right to give the exposure needed 
for whatever you're point the camera at, and I think any photographer who 
used such a camera and found no meter deflection would instinctively move 
the camera around and/or turn the aperture ring to check the meter was 
working. I know I would. My view is thath te Spotmatic meter is a bodge!

> 
> If you want an appliance, yes, it's important to not let yourself fall too =
> far behind the curve.  But if you're a manly man (or a womanly woman) and s=
> eek great adventure and even greater glory (and perhaps even an advantage w=
> ith members of the gender of your choice), you'll geek-up and do what it ta=
> kes to keep your Olde Beaste running. =20

Yes, it deepends on what you want to do. If you want to run the lattest 
software, you need a modern-ish computer. But I am quite happy using this 
classic for e-mail, text processing, etc. It does all I need. And I 
understand how it works and how to keep it working. 

-tony



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