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Old 24th Oct 2020, 5:06 pm   #1
Rich Woods
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Question 1960 GEC BT302 Contrast Issues

Hi, I haven’t posted on here for a while as my BT302 has been running faultlessly. Famous last words. Over the last couple of months the contrast control has got flaky, you could get about 1/2 way up the dial with the contrast working properly and then on increasing further it would crash down to minimum contrast. The situation has got worse and now the contrast control makes little difference at all and seems to be at minimum contrast. I’ve tried replacing the 30F5’s again but this time with little difference. I’ve ordered turret tuner valves, PCF80 & 7AN7 but I’m not wholly convinced that this is the answer. I would be grateful for any thoughts or tips from the forum that might help. Cheers.
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Old 24th Oct 2020, 8:15 pm   #2
Kyle__B
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Default Re: 1960 GEC BT302 Contrast Issues

Have you tried replacing the control?
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Old 24th Oct 2020, 9:26 pm   #3
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Default Re: 1960 GEC BT302 Contrast Issues

First check as KB has suggested, check the control.
If the picture is grainy, replacement of the PCC84 and PCF80 tuner valves should sort it out.
If grain free I would suspect a high value resistor in the AGC control circuit possibly R38 680K, [AGC line]R123 1m [slider of contrast control] R22 1m [AGC line] R33 1.8m [AGC line]
Possibly a faulty decoupling capacitor. AGC line, C45 .5uf, C44 1uf. These are first checks.
Fault could be in video amp. Check both 12k anode load resistors R44 R45 10k. common vision and sound I.F. V1 could be low emission but they are very reliable valves so maybe unlikely. Good luck with it. Nice and simple TV receivers. John.
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Old 24th Oct 2020, 10:02 pm   #4
Rich Woods
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Default Re: 1960 GEC BT302 Contrast Issues

Control seems OK thanks. Have ordered turret valves. Will try first & then go on to the components. Cheers for the help, Rich
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Old 28th Oct 2020, 4:09 pm   #5
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Default Re: 1960 GEC BT302 Contrast Issues

Turret valves did the trick! Thanks for the advice. Rich
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