Simpson 430 color bar generator

[miniman82]

This was a steal at $99 BIN on Ebay, shipping free!





Note the nice copper chassis free of corrosion, and the more important fact that it provides 100% saturated bars along with I and Q color outputs. This should make set up of vintage color receivers a lot easier, as later bar gens provided 75% saturated bars in the wrong order. I've already tried it out on my Sony monitor and it does work, but something's amiss with the RF output. So I'll figure out what's wrong with the RF generator, then run through the alignment in the manual and post up a screen shot to see how it looks.

[old_tv_nut]

The I and Q bars will be useful, but caution on the 100% amplitude saturated color bars. It is not possible to modulate them linearly on the RF, because the peaks of the chroma represent 33 percent over-modulation; this is why later bar generators went to 75% amplitude bars. The over-modulation affects both the RF modulator in the generator, and the envelope detector in the receiver, particularly on the yellow and cyan bars, in unpredictable ways. The NTSC standard was set up this way to make the chroma signal less noisy, under the premise that these high levels would seldom be reached with real picture signals.

If you are going to use color bars through the tuner input to check the matrix in a CT-100, for example, you should use the 75% bars and adjust for rectangular waves of 75% amplitude compared to the 100% white bar. If your set has been jeeped to add a composite baseband video signal input, the 100% bar video can be used there without problems.

[Username1]

Oops.... So are the levels static on that machine, or are they variable, or selectable...?

Very nice looking generator.... Also a plus that it has rf outputs... I got a really old one
I think it's a rca with only direct connect clipleads to guns..... If I knew that I would
have never bid on it..... That one looks really cool.... So many tubes in it ! !

Nice front panel too ! !

[miniman82]

Wayne you are correct about the over modulation part, but I suspect that when testing various chassis the input was composite not RF. I can't think of any other reason why the manuals would state 100% saturated bars unless that were so, because it would lead to clipping of the top half of the signal. Not sure what that would look like on screen, but I suppose I can test and find out.


I haven't done anything to it but touch up some of the controls to make the bars as even as possible and even out the chroma and Y intensity, and already it makes great colors on my Trinitron without any parts replaced. I can see using the heck out of this thing, even if only as a demonstration piece.

Ignore the cyan bar bleeding over into the white, for some reason the camera picked it up but it's not nearly that bad in real life.

[old_tv_nut]

Nice picture - is that video in or RF?

One way the distortion may go: The modulator may not be able to go to 100% modulation and actual clipping, and may have residual carrier at the signal peaks. This could be worse at higher channels. Depends on the layout and stray coupling. Another thing, the unit may just be undermodulated so that it is just not trying to make over 100%. A modern wideband scope is able to display the modulated waveform at low VHF channels and could tell you how well behaved it is.