50Hz vs 49Hz - Vintage Polish Computer Terminal

[MightyFrame]

So, I went to Poland last fall and brought home this beautiful computer terminal, possibly the first one ever in the USA.

Of course it's designed to run on 220v 50Hz, no surprise, and we have 120v 60Hz here in the USA. We can easily get 240v of course, but it's still 60Hz.



Now, knowing this, I bought a 12v to 220v 50Hz inverter that is supposed to support European "appliances".

But when I try to power up this terminal with it, this happens:

https://www.youtube.com/watch?v=0f1xM0PDezc

Is this obviously the 49Hz vs 50Hz that I originally noticed, or could this be something else?

Appreciate your opinions here, always.

Best,
AJ

[AlanInSitges]

IME the 1Hz difference won't cause much if any problem. But if that thing is designed for 50Hz and running on 60Hz, the ripple from the power supply will beat with the vertical scanning frequency and cause the image to vibrate quite a bit. I have a Predicta and a couple of PortaColors here in Europe that are unwatchable when fed a 60Hz NTSC-M signal but running on 50Hz. N.b., Shango did a video a year or so ago where he solved a similar problem of trying to feed a modified 24FPS signal from a telecine to a Sony TV and ultimately I think he fixed it by adding a ton of capacitance to the power supply.

In your case I suspect the problem is more likely related to the cheap inverter you're using - they call them "pure sine wave" but they are neither pure nor sine wave. Most of them output a messy "modified" sine wave that will wreak havoc with the old linear power supply in that terminal. They look something like this:


There are evidently some that output a cleaner form of AC but I have tried two different ones sold as "pure sine wave" that looked that way. TV's don't like them, and neither do 60Hz motors in record changers, at all.

If I were you, I'd try using a 2:1 autoformer (these are fairly cheap) to feed 220-240V 60hz power to the terminal and see what happens. Going from 60Hz to 50Hz is difficult because of the higher ripple coming from the power supply, but going the other way might not be as bad, or even problemmatic at all. At the very least you'll be able to tell whether the issue you're seeing is due to the dirty AC power from the inverter or a failure in the terminal itself.

[MightyFrame]

Thank you, Alan, this is a very helpful reply.

Since 240v is easily available in my own home, I might as well just connect it to that and hope for the best. That should be as stable 60Hz as I can get, and hope that the 60Hz vs 50Hz won't make that much of a difference.

I was thinking that the inverter would be "safer" for testing, but perhaps not?

It's just such a rare machine (outside of Poland anyway), that I didn't want to risk blowing up those soviet-era components that make up the whole thing. So I appreciate your experienced opinion on that.

Thank you again!

Best,
AJ

[old_tv_nut]

I hope the designers didn't do something silly like sync the vertical to the power line to make power supply hum stationary. Waiting with bated breath to see the results with 60 Hz power.

[Electronic M]

Originally Posted by AlanInSitges

IME the 1Hz difference won't cause much if any problem. But if that thing is designed for 50Hz and running on 60Hz, the ripple from the power supply will beat with the vertical scanning frequency and cause the image to vibrate quite a bit. I have a Predicta and a couple of PortaColors here in Europe that are unwatchable when fed a 60Hz NTSC-M signal but running on 50Hz. N.b., Shango did a video a year or so ago where he solved a similar problem of trying to feed a modified 24FPS signal from a telecine to a Sony TV and ultimately I think he fixed it by adding a ton of capacitance to the power supply.

In your case I suspect the problem is more likely related to the cheap inverter you're using - they call them "pure sine wave" but they are neither pure nor sine wave. Most of them output a messy "modified" sine wave that will wreak havoc with the old linear power supply in that terminal. They look something like this:


There are evidently some that output a cleaner form of AC but I have tried two different ones sold as "pure sine wave" that looked that way. TV's don't like them, and neither do 60Hz motors in record changers, at all.

If I were you, I'd try using a 2:1 autoformer (these are fairly cheap) to feed 220-240V 60hz power to the terminal and see what happens. Going from 60Hz to 50Hz is difficult because of the higher ripple coming from the power supply, but going the other way might not be as bad, or even problemmatic at all. At the very least you'll be able to tell whether the issue you're seeing is due to the dirty AC power from the inverter or a failure in the terminal itself.

One small correction. The OP will have LESS ripple at 60Hz than at 50Hz. 50Hz equipment will have bigger filter caps by design than the same model built for 60Hz. Bigger filters reduce hum ripple. You're use of 60Hz sets on 50Hz will increase hum because you have the opposite scenario of the OP.
It will have more noticable hum in the scan because when the frequency of hum and vertical are substantially different it makes the hum that is there easier to see.


It should be perfectly safe to run it on 60Hz. The transformer should run cooler and the filters should be bigger than needed and work better. I regularly run a 25Hz Canadian Zenith and periodically run a 50Hz Philips TV on 60Hz and both do fine with it.