PET composite video adapter

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 as being from the "Commodore Pet Users Club of England - Newsletter issues 1 & 2, page 9". It's the variant with three NOR gates ('LS02), with a few resistors, capacitors, and a diode. The part that I'm curious about is how much variation is allowed in the caps. 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 large lying around. The output of that gate (which NORs the inverted vertical sync with the massaged horizontal sync) feeds unto a "47mf" tantalum cap (then pulled down to ground by a diode, and wire-ored to inverted video out/composite out via a 470 Ohm resistor). I have 47uF caps, but that seems pretty large to me. I have a basic understanding of RS-170-type video, and I know this circuit is probably going to produce a signal that "modern" IC-based video inputs will not like (much the same way the classic RCA CDP1861 video behaves), but fortunately, I have an old B&W security-type monitor to plug this into (which has already been tested with a CDP1861). I'm just curious why the caps are so large. I think I get what's going on with this circuit (the way it combines the syncs and video), and I've heard of similar circuits being used successfully by others, so with luck, it'll work the first time. Oh... in case anyone is wondering why I'm bothering, I have a couple of naked PET boards here, no chasses, no CBM monitors. I did cobble up a DC-based harness (+5, +12, -5V, no tape motor voltage, but then no tape drive, either) for testing, and I do get "interesting" looking pips on a 'scope when I check for video, so I'm hopeful that the boards are working well enough to at least give me a screen full of _something_, even if it's the classic "garbage" screen you get when the machine isn't running well enough to zero video RAM. So has anyone here made an external PET video adapter and have any experiences to share about what worked and what might not have worked? Thanks, -ethan P.S. - I found another type of composite circuit using a CD4011 as an inverter and a CD4066 to mix the signals, but for some reason I don't have all the components labelled on my drawing - the cap on hsync in particular. One interesting variation with that one is that the 'LS02 circuit has a 1.5K pulldown on hsync between the cap and the gate, while the CD4011/CD4066 circuit has a 10K pot. How much adjustment on hsync is likely to be needed between the PET and the first gate of the composite circuit? -- Ethan Dicks, A-333-S Current South Pole Weather at 13-Oct-2008 at 03:50 Z South Pole Station PSC 468 Box 400 Temp -54.4 F (-48.0 C) Windchill -76.4 F (-60.2 C) APO AP 96598 Wind 5.1 kts Grid 65 Barometer 671.7 mb (10943 ft) Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html