monitors for use with old computers.

Right. The most important thing to match up when selecting a monitor is the horizontal scan rate - since (in 99% of cases) the EHT (and other voltages) are produced by the horizontal output stage, changing this scan rate is almost always non-trivial. The vertical scan rate is much easier to fiddle with, since nothing else is produced by the vertical deflection system. Fortunately, almost all home computers (and all the ones you mentioned) use TV-like scan rates. In the UK, they're 15625Hz horizontal, 50Hz vertical, while in the States they're 15750Hz horizontal (I think), 60Hz vertical. Those 2 horizontal scan rates are close enough that most monitors for one can be tweaked to work at the other. Now, as to the video signal itself. It will typically be one of a small number of possibilities : 1) Digital RGB colour (BBC, for example). This has 1 TTL level signal for each of R,G,B, and hence you're limited to 8 colours. The Syncs are separate TTL level signals, either separate (HSync and VSync) or combined (Composite Sync). Amstrad used a varient of this system where each of the R,G,B signals could be in one of 3 states (high, low, floating) giving 27 colours. 2) Analogue RGB colour. This has separate analogue signals for each of R,G,B, giving essentially unlimited colours, but is otherwise as in (1). Sometimes the Sync signals are combined with the green video signal (sync-on-green). 3) Monochrome with separate syncs (very rare!). This system has a single signal (either analogue or digital) that carries the intensity information, together with 1 or 2 sync signals as above. I can't think of a home computer that used this system 4) Composite monochrome. This combines the syncs and intensity information into a single signal that is almost identical to a TV video signal (i.e. what you'd find in a TV after the video detector, or what you'd get from the video output socket on a VCR). These signals are almost always compatable with the TV standards of the appropriate country. 5) Composite PAL or NTSC. PAL and NTSC are the systems used in the UK or the States for colour television. These signals are in general compatable with the TV standards of those countries, and combine all colour, intensity and sync information into a single signal. 6) 'Y&C' (Commodore, in general). The colour TV signal consists of 2 parts - the 'Y' (or luminance) signal which caries the intenstity information and the 'C' (or chrominance) signal which caries the colour information. Some CBM machines have separate outputs for the 2 signals, which gives slightly better quality than combining them and them separating them again in the monitor. 7) VHF/UHF TV signals. These are essentially very low power TV transimissions, on Channel 3/4 (VHF) in the States, and Channel 36 (UHF) in the UK. You link them to the aerial input of at TV set, which then converts them to Composite PAL/NTSC. Now, as to what converts to what easily : Composite PAL/NTSC and Composite monochrome are compatible in both directions with no problems. The TV standards were designed that way. VHF/YHF TV can be converted to composite video using a TV tuner/IF strip, either as part of a TV, or extracted from a dead VCR. There are single-chip solutions to convert composite PAL or NTSC (and even some chips that do both) to analogue RGB. Be warned that _building_ a circuit using one of these chips is often hard, since there are a number of critical adjustments to get right. There are also single chips that go the other way Digital RGB outputs will often drive analogue RGB inputs, sometimes a resistor network is needed. The other way needs a few high-speed comparator chips (although _sometimes_ a direct connection works!) There are chips that will separate the syncs from a composite signal, and produce video + syncs. Combining syncs and video to make a composite signal is generally a simple circuit as well. Well, there have been monitors (Philips, Barco, a few others) that will accept : Composite PAL (and hence mono). A few do NTSC as well Digital RGB Analogue RGB Take one of those, add a TV tuner, and you can handle just about all the standards. Some _good_ portable TV's have a SCART socket with RGB inputs. The bandwidth there is often high enough to enable the set to be used as a monitor for (at least) 80 column text. A SCART socket will also have a composite PAL input on it. And of course a TV will accept UHF or VHF signals as appropriate. Apart from special monitors, I make do with 3 things : 1) A portable (9") NEC monochrome monitor. Composite inputs 2) A digital RGB monitor (again NEC, although I'd prefer a Microvitec) 3) An analogue RGB monitor (Barco, big, heave, expensive!) -- -tony ard12(a)eng.cam.ac.uk The gates in my computer are AND,OR and NOT, not Bill