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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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24th Oct 2020, 5:06 pm | #1 |
Pentode
Join Date: Sep 2017
Location: Ceredigion, Wales, UK.
Posts: 243
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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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24th Oct 2020, 8:15 pm | #2 |
Banned
Join Date: Mar 2020
Location: Nijmegen, Netherlands
Posts: 142
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Re: 1960 GEC BT302 Contrast Issues
Have you tried replacing the control?
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24th Oct 2020, 9:26 pm | #3 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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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. |
24th Oct 2020, 10:02 pm | #4 |
Pentode
Join Date: Sep 2017
Location: Ceredigion, Wales, UK.
Posts: 243
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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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28th Oct 2020, 4:09 pm | #5 |
Pentode
Join Date: Sep 2017
Location: Ceredigion, Wales, UK.
Posts: 243
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Re: 1960 GEC BT302 Contrast Issues
Turret valves did the trick! Thanks for the advice. Rich
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