TTL homebrew CPUs

Tony Duell ard at p850ug1.demon.co.uk
Thu Jul 12 16:50:45 CDT 2007


> 
> On 12 Jul 2007 at 19:53, Tony Duell wrote:
> 
> > ]1] Called 'Photoflash' or 'Hearing Aid' batteries in the old books. The 
> > fomrer because they were used to charage a capacitor of About 100uF to 
> > fire the old single-shot flash bulbs. 
> 
> Now, I thought that the "photoflash" appellation was due to their 
> being used in early photo strobe flashes.  I can still remember 

I did read of an early gas-discharge flash unit that used 8 30V batteries 
in series to get the high voltage

[Totally useless bit of trivia. In the UK there were 2 series of these 
batteries : 

B154 (15V), B155 (22.5V), B156 (30V). These were ssqare in cross-section, 
the side of the square being about the same as the diameter of an AA 
cell. The B155 was actually about the same length as an AA cell too)

B121 (15V, B122 (22.5V), B123 (30V), These were rectanglar in 
cross-section, width about twice the thickness. The thickness and length 
were about the same as the equivalent-voltage version in the other series]

Certainly in the Europe, many bulb-type flashguns used 22.5V (or 15V) 
batteries in what was commonly called the 'battery-capacitor circuit). 
The simplest form was this : 

               3k-ish              Flashbulb  
         +----/\/\/---------+-------(X)---------+
         |                  |                   |
      -------               |                   |
        ---                 |                 ===== 100uF-ish
      ------- 22.5V         o                 ----- 
        ---                  \   Shutter        |
         |                  o  \ contact        |
         |                  |                   |
         +------------------+-------------------+


When there's no flashbulb inserted, there is no load on the battery at 
all, not even leakage through the capacitor. When you insert a bulb, the 
capacitor charges to the battery voltage through the bulb and the 3k 
resistor, the latter limiting the currrnet so that the bulb doesn't fire. 
When you take the picturem, the cynchronisation contacts in the shutter 
close, connecting the capacitor diresctly across the flashbulb and 
causing it to ignite.

Some flash units had a test lamp that indicated the flashbulb was good -- 
that the ignition filament was intact. The normal way this was done was 
to connect a small lamp in series with a push switch aross the capacitor. 
Pressing said switch would discharge the capacitor through the test lamp, 
causing the latter to light briefly if the capacitor was charged. That 
would only happen if the flashbulb was intact.

> lugging around a Honeywell Strobonar that used a pack holding two 
> rather large 225v batteries--attached to the strobe head attached to 
> my Rolliflex.    Recycling time was very fast--most sports 
> photographers wouldn't have been without them.  There were also 510 
> volt batteries for more compact flashes.  

Indeed, and those were used until quite recently (say 20 years ago). I've 
seen a 'Sunpack' flash unit which has an extermnal PSU conenctor 
(connected IIRC, to the terminals of the main capacitor through a diode 
and limiting resisotr). Listed accessories included a mains power pack 
and a battery holder for a 510V battery. The advantage of this was a very 
quick recharge time, of course.

>From what I've read (and, alas, I don;t have any ancient gas-discharge 
flash yuniots), there were basically 4 tuypes of paower pack used to get 
the high voltage (a few hundred volts) for the flash tube : 

1) Mains transformer + rectifier
2)  Battery + Vibrator + transformer. The Battery was often a wet-cell 
lead-acid accumulator
3) HV battery
4) Transistorised oscillator + transformer (once transistors were in 
common use)
 
-tony




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