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While waiting for the NTE diode I played with improving the
picture. The set uses a very very odd contrast control system
using a pot in the video amplifier cathod and two bypass caps,
one 150 and one 820 pF. The frequency response varies
tremendously with contrast setting.
I found an improvement: add from the cathode to ground
two things: one is a .0012 uF cap, the other is a series
combination of 47uF and 390 ohms. This does mean the
contrast can't be turned as far down, but the frequency
response becomes quite flat from 1/3 full gain (control
about 80% up) on down. At full gain there is a 6 dB
enhancement at low frequency, but this generally is too
high a setting.
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