13 Oct
2008
13 Oct
'08
1:57 p.m.
On Mon, Oct 13, 2008 at 08:38:30AM +0100, Tony Duell wrote:
I do not. I have a jpg file that I acquired some time ago from I know
not where.
Of course. I never thought it was millifarad.
Hi, All,
I'm just finishing up assembling a PET "Video Mixer" from an old JPG
of a much older scan of said circuit. This particular one is annotated
Do you have a URL for said scheamtic? The schematic
shows the horizontal sync coupled to a gate via a "2200 mf"
non-polarized cap. I don't know that I have any disc or ceramic caps that
IO think we can instantly eliminat 'mf' == millifarad (which is what it
should be!), since that's then 2.2F, which is rediculously large 2200uF (microfarads) is also IMHO too large for a
non-polarised
capacitor, I've not seen non-polarised electrolytics that large, and
anyhting else would be essentially hopeless. 2200uF as an aluminium
electrolytic would be very possible.
Agreed.
2200nF (==2.2uF) would be possible, but it's a
very odd way to write it.
Yes. This was also written in the 1970s, so I'm trying historical
interpretation as well as what's obviously written.
2200pF (==2.2nF) is quite possible, for some reason
some people
(particularly in the States) don't like the unit 'nF'. That would also
seem to be a suitable value for coupling a 15kHz signal.
2200pF does sound reasonable. I am one of those who never grew up
using nF, so I don't tend to use it (I learned milli-microfarad from
my father for pF, he, in turn, was a Ham in the 1950s).
Well, tatalum caps tend to be in the range 0.47uF to
100uF (yes, they
exist outside that range, but they're less common). so 47uF would be
possible.
Possible, but it seems large.
Whenever I've wanted to combine syncs and video,
I've used a circuit
rouhly based on the TRS-80 Model 1 video output and/or the IBM PC CGA
composite output. No capacitors involved. An XOR gate to combine syncs, a
couple of transistors and a resistor chain. Never had any problems with it.
This is probably a transistor-less version of a similar circuit. It has
NORs rather than XORs (though I've seen that one) and a resistor chain,
but no transistor.
I don't know why there's a cap and a pull-down diode between the sync-combiner
and the sync-and-video combiner gates, but it's there. I was guessing the
cap was on the horizontal circuit, along with a pull-down resistor, to act
as an RC delay of some sort to allow one to tweak the horizontal sync slightly
to match up with whatever external monitor one is using, but I could be
wrong about that.
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 13-Oct-2008 at 20:50 Z
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Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html