16th Jul 2010, 4:34 pm | #141 |
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Re: GEC BT1156 First Light & Vidor CN4216
There are different sorts of diodes, but yes MR3 is a diode - of the rectifier kind.
Cheers, Steve P.
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16th Jul 2010, 5:41 pm | #142 |
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Re: GEC BT1156 First Light & Vidor CN4216
Again two steps forward 5 back....!!!
Snipped the old MR3 put the IN4007 in circuit and powered up. HT ended up at 228V. The testcard was lot larger and I adjusted it to fit, the top squiggle was there and would not go. I stated to look at the circuit and whilst I was doing so I heard the test tone fade I went and looked at the screen, Test card gone just a blank raster. Resoldered the old MR3 back in and it's still the same you can just hear the tone to start with upon power on, no test card just blank raster and eventually the tone cannot be heard. Damm! |
16th Jul 2010, 6:04 pm | #143 |
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Re: GEC BT1156 First Light & Vidor CN4216
Check the tuner connections.
Did you put any form of resistor in series with the 1N4007? You really need to. Cheers, Steve P.
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16th Jul 2010, 6:09 pm | #144 |
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Re: GEC BT1156 First Light & Vidor CN4216
Yes I did as Trevor recommended lastnight a 47R
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16th Jul 2010, 6:28 pm | #145 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Chris.
Often this is the case when replacing rectifiers. A silicon diode is a compromise I am afraid in comparison to a metal rectifier. The forward voltage drop is much lower on a IN4007 so when the valve heaters are cold 300v can be across the smoothers and the other components, anything thats a bit long in the tooth can then fail as the original metal rect will never give 300v off load. I very rarely will replace a metal rectifier with a IN4007 unless the set has been fully gutted, my Murphy V320A has been extensivley "repaired" and uses a BY127 (an old silicon rectifier) and is 100% reliable. My usual mod though for duff metal reccy's is to fit a PY33 rectifier valve, you then have the benefit of slow HT build up and you never have that awful 300v off load voltage. It does need some changes to the circuitary though.
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16th Jul 2010, 6:37 pm | #146 |
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Re: GEC BT1156 First Light & Vidor CN4216
Oh well back to the drawing board, Thought I was almost there when I had a nice full testcard. This certainly tests the will power.
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16th Jul 2010, 6:56 pm | #147 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Chris.
Remember you still have a lot to learn and as I have said before it takes a long time. One big advantage you have is that there is not a screaming customer on the end of the phone or in the shop. Think of it this way you are doing this as a hobby and if you have the patience to persevere with a set you will enevitably be better than a 50's or even 60's engineer, less of course the relavent papers.
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16th Jul 2010, 6:57 pm | #148 |
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Re: GEC BT1156 First Light & Vidor CN4216
Back on track...................
I will not be beaten, as can be seen from my mammoth sessions |
16th Jul 2010, 6:59 pm | #149 |
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Re: GEC BT1156 First Light & Vidor CN4216
What is the HT now?
Remember the 47 ohm may be too high, your running HT still may be lower than spec. Regarding your comment "I wont be beaten" Please never get cockey, everyone will be beaten sometimes! You wouldn't be asking all these questions if you knew it all!!
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16th Jul 2010, 7:04 pm | #150 |
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Re: GEC BT1156 First Light & Vidor CN4216
I'm back on the original GEC metal rectifier, not doing the IN4007, going to see what else is possible.
The loss of Testcard was two knackered tuner Valves PCC84 & PCF80 I need to find a better place to probe HT without having to keep up ending the chassis. I have 318V A1 EHT is way off still only running 8.2kV |
16th Jul 2010, 7:10 pm | #151 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Chris.
The low EHT & lack of width are related, have you checked the line o/p valves screen feed and grid 1 resistor as I suggested earlier on in the thread? Can you also tell me what the HT is now is it up to spec?
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16th Jul 2010, 7:16 pm | #152 |
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Re: GEC BT1156 First Light & Vidor CN4216
Ok Trevor,
Just going to have a breather and a nibble, I will get back on that. I'm having trouble getting used to PCB layouts and not seeing the valve bases just blobs of solder and cannot reach in or determine whats what. |
16th Jul 2010, 7:18 pm | #153 | |
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Re: GEC BT1156 First Light & Vidor CN4216
Quote:
Ok my man! Standing By
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16th Jul 2010, 7:46 pm | #154 |
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Re: GEC BT1156 First Light & Vidor CN4216
Trevor,
HT measured on MR3 Cathode 174V on anode 3.9mV. C110 0.01uf, R117 3.9k c111 0.01 all ok. R114 is 840K I think I had tested that previous but ignored it as it was within 20% but as you say only 10% then I will change it. ------------------------------------------------------- It's one thing after another with this set. now the combined on/off volume switch does not switch the set off, it just turns the volume up and down or off. When switched on/off the TV stays on all the time. I bet finding another combined on/off/volume/contrast pot will be as easy as finding hen's teeth. I fear another mod will be required to provide on off switching. Tried turning off and it worked, tried again and it did not, intermittant then. ------------------------------------------------------- I guess when the HT & EHT are sorted out the picture will be outstanding, because even at this level it's pretty good. Last edited by oldticktock; 16th Jul 2010 at 8:09 pm. |
16th Jul 2010, 8:10 pm | #155 |
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Re: GEC BT1156 First Light & Vidor CN4216
Great work so far Chris.
I find the exact opposite. I think that PCB's are easier to follow. I especially like the early GEC printed circuit boards as they are so robust unlike the double sided print when they joined forces with Sobell
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16th Jul 2010, 8:15 pm | #156 |
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Re: GEC BT1156 First Light & Vidor CN4216
Hi Chris.
Squirt some WD40 (not switch cleaner) into the switch part of the On/Off vol control, this will lubricate and soften the grease that has hardened on the mechanical part of the control you will need to operate the switch many times along with plenty of the WD40, this should cure that problem. Change R114, it can be quite critial on some sets but regarding the GEC only you will know if there is an improvement!
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16th Jul 2010, 8:24 pm | #157 |
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Re: GEC BT1156 First Light & Vidor CN4216
Thanks Taz, If I had been an engineer in the 50's I would have been one of the old geezers complaining about the new fangled nonsense
Hi Trevor I take it it is the very back section (the black one) as that's where the mains fly leads from the fuse board hit. Do I just lift the tags a little and squirt, not done this before and I'm concerned to get it right and not make it worse. Last edited by oldticktock; 16th Jul 2010 at 8:30 pm. |
16th Jul 2010, 8:29 pm | #158 |
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Re: GEC BT1156 First Light & Vidor CN4216
Chris.
Try not to lift anything from the control, you can squirt the stuff into the rear control and around the plastic of the switch, usually enough will track into the switch.
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16th Jul 2010, 8:30 pm | #159 |
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Re: GEC BT1156 First Light & Vidor CN4216
I've just woken up. Exercises on my leg then sleep. Didn't those tuner valves choose the perfect time to fail. I often wonder if old tellys do have feelings and an awful sense of humour.
Change the valves and the resistors in the line stages and then hopefully that should be it. I would then try that diode again with a bigger resistor to bring the HT up a bit. Then have a rest. Taz - It's purely what you are used to old bean. PCBs are OK until somebody who can't solder gets involved with them. A number of the earlier ones have problems with tracking. Cheers, Steve P.
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16th Jul 2010, 8:39 pm | #160 | |
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Re: GEC BT1156 First Light & Vidor CN4216
Quote:
You have woken up too quick, A smaller value resistor is needed for higher HT.
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