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Old 02-04-2017, 08:25 AM
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Gleb Gleb is offline
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Join Date: Mar 2015
Location: Russia
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Quote:
Originally Posted by Phil Nelson View Post
Would you mind sharing the details of this circuit?
Phil, better late than never, sorry for delay. If a CRT is driven the 'classical' way (the signal to the cathode, the brightness control to the 'grid'), it comes pretty simple:




Just cut up the wire from the CRT's grid, and connect a 150-200k potentiometer to the gap. Then take a signal from the vertical oscillator tube's plate, and feed it to the CRT's grid through a capacitor of a few thousand picofarads. Balance the potentiometer to blank the retrace lines completely and not to let the picture get distorted. Then measure the actual resistance of the potentiometer, and install a resistor of the closest value instead of it.
It gets more tricky if the CRT is driven the 'odd' way (the signal to the grid, the brightness control to the cathode). In such a case, the flyback pulses from the vertical oscillator have the 'wrong' polarity to feed them to the cathode of the CRT. So you have to get them from the plate of the vertical output tube where the flyback pulses are dirty and distorted by the reactance of the vertical deflection coils and/or transformer, and need to be extra cleaned and shaped before feeding them to the CRT.
Attached Images
File Type: gif retrace_blank.gif (26.2 KB, 93 views)

Last edited by Gleb; 02-05-2017 at 05:17 PM. Reason: addition
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