OK, Tim...
You're partly (OK, OK, _mostly_!) right -- I'm partly (yeah, OK,
_mostly_!) wrong! ;^) The recycle time _does_ vary significantly, but
the T-20 _does_ use a quench tube.
My appologies to the list, with this explaination:
The T-20 _does_ have a quench tube (I was sure it did -- I remember
seeing them!) -- but uses it in an "energy saving" circuit!
One seldom, if ever, gets to call a quench tube circuit "energy saving",
but some devious, crafty designer found a way. I had to check, but
there it was -- page A-14 of the T-20's repair manual (one of the few
really _good_ manuals from that era)...
When SR-103 fires (see flash intensity control circuit), C-108
discharges through T-103 (the quench tube's trigger coil), "firing"
B-202 (the quench tube).
But here's where it gets interesting! Rather than using this to simply
dump the power of the main cap away from the flash tube to interrupt the
flash (like most early auto-flashes), C-105 discharges through B-202,
_but_ since R-136 is in the way, a portion of the current is diverted
_back_ up the circuit, to the "K" leg of SR-104! In other words, it
kicks the SCR in the back-end! That causes SR-104 (the SCR) to "change
state", from conductance to non-conductance -- it switches off the power
to the flash tube! Kewl, huh?!
Actually, we almost never need to know this stuff -- when they don't
work, we usually just check a couple of diodes and transistors, replace
any parts that have cooked, and hope!
HI100@xxxxxxx wrote:
>
> Clint wrote:
>>
>> The T-20 uses a "quench" tube to control the output, meaning it
>> effectively "dumps" full power every time it's fired. That means the
>> recycle time will not vary significantly.
>>
>
> Hi Clint,
> the e SIF archives disagrees with you on this one :
> " Energy-saving, series-circuit type, system electronic flash unit. "
>
> It is also pretty easy to test and show that the recycle time varies with
> distance on both ttl auto and flash sensor auto.
>
> My memory is that it is a conventional SCR energy saving circuit.
> Even the A16 flash in the XA is an SCR unit.
>
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