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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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6th Sep 2014, 8:46 pm | #21 | |
Heptode
Join Date: Apr 2003
Location: Cornwall, UK.
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Re: Philco upside down TV.
Quote:
SimonT.
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6th Sep 2014, 10:01 pm | #22 |
Dekatron
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Location: Warnham, West Sussex. 10 miles south of DORKING.
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Re: Philco upside down TV.
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6th Sep 2014, 10:19 pm | #23 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
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Re: Philco upside down TV.
Well that's the frame timebase sorted. The big surprise is that it was not the usual suspects C47 or C49 as correctly suggested by Simon but the 500pF mica capacitor C46.
One tends to forget about these mica capacitors, "they never go faulty" Well they do. Anyone who does radio repairs will often report that a mica capacitor has failed. The line oscillator often fails in the Ekco TS88 and TS105 series TV receivers and the usual suspect is the 100pF mica capacitor in the miller transitron oscillator. I supplied the Philco with signals from an Aurora converter , no results irrespective of which Band 1 channel was selected. So I still the front end of the set to sort out. DFWB. |
8th Sep 2014, 12:44 pm | #24 |
Dekatron
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Location: Gateshead, Tyne and Wear, UK.
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Re: Philco upside down TV.
More progress with Philco yesterday. Voltage measurements at the base of V1 (6F13) revealed that the cathode volts were to high irrespective of the setting of the RF gain control. The slider of the 10Kohm variable resistor is not making contact. For the time being the control has been bypassed to ground. Still no signals coming through from the Aurora just a very faint test tone on all channels.
Next, I turned my attention to the local oscillator. the voltage on C7A is too low, only 40V. R7 checks out OK as does C7A for leaks. It turned out that the adjustable iron dust core of the oscillator coil was touching the coil. Centralising the core effected a cure, the volts on C7A have rising to 90V. Still no signals though. Turned out that the tuning capacitor C6 was faulty. That sorted pictures and sound are coming through, on channel 3! I've retuned the set to the Birmingham frequency. Anyway the good news is that CRT is excellent, it's one of the brightest Mazda CRM92 tubes I've seen for a long time. There are still few jobs left to do. The sync separator function is bad, the frame and line hold could be far better. Also the HT voltage is low, only 175V. It should be in the region of 250 volts for this set. A replacemnt metal rectifier will have to be found. DFWB. |
8th Sep 2014, 1:07 pm | #25 |
Octode
Join Date: Jan 2009
Location: Falmouth, Cornwall, UK.
Posts: 1,987
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Re: Philco upside down TV.
I remember the tuning capacitor on my Ekco TC169 was faulty too, that kept me going for at least a week.
Good news on the tube.
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Stephen _________"It`s only an old telly" ___ |
8th Sep 2014, 2:19 pm | #26 |
Octode
Join Date: Feb 2006
Location: Ilkeston, Derbyshire, UK.
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Re: Philco upside down TV.
I'm looking forward to seeing photos of this set when David's done his magic. I don't think I've ever seen one working!
I have a Philco BT1840 that also uses this chassis. It certainly turned up in some very varied models. Steve |
8th Sep 2014, 3:41 pm | #27 | |
Dekatron
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Location: Gateshead, Tyne and Wear, UK.
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Re: Philco upside down TV.
Quote:
Armed with all this servicing experience gleaned from the Defiant and my Philco I look forward to seeing your Philco on my next visit later this year. The BT8140 has a very American appearance, even has a radio receiver. You can imagine that there was a similar looking set Stateside. The attachment shows small picture due to the low HT voltage. DFWB. |
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8th Sep 2014, 4:06 pm | #28 |
Octode
Join Date: Feb 2006
Location: Ilkeston, Derbyshire, UK.
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Re: Philco upside down TV.
Excellent David, that looks very promising.
Are you actually going to try and find another NOS rectifier or hide a sneaky diode & resistor combination somewhere, leaving the original finned device in situ? Steve PS- Yes, let's have a delve inside my Philco on your visit next month. It's almost a shame to disturb the cobwebs. It looks like something out of horror film in there. Quite appropriate that you'll be visiting around Halloween! |
8th Sep 2014, 4:13 pm | #29 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
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Re: Philco upside down TV.
Hi Steve,
I'll take a look upstairs, you never know there might be a good metal rectifier up there. Incidently, the little Philco is one of the first sets to be worked on in my garden workshop. DFWB. |
8th Sep 2014, 4:57 pm | #30 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
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Re: Philco upside down TV.
The infamous G1 cap.
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8th Sep 2014, 6:41 pm | #31 |
Dekatron
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Location: Gateshead, Tyne and Wear, UK.
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Re: Philco upside down TV.
I removed the finned HT rectifier from this Plessey Mark 3? chassis. It was tried out in the Defiant. Guess what happened? Sparks and finally a bang, then the fuses blew. Accompanied with that familiar smell.
So I'll have to find another Westinghouse 14A96. DFWB. |
11th Sep 2014, 8:25 am | #32 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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Re: Philco upside down TV.
Just fit a BY100 and a 30 ohm surge limiter David. Not worth stinking the house out attempting to get one of those old stink bombs to fire up [!]
If you can find an AUTOMAT rectifier from an Ekco, you will find it to be 100%. Problem is the length will not fit the Plessey chassis. I had a look in my junk box and discovered this lovely little selection...I only keep them for old times sake. I have a hilarious story regarding stinking EHT triplers but will save it for a more suitable thread. Regards, John. PS Just tested the RM4 and the blue painted one and discover they are 'OK'. Your welcome to one if you want to do a bit of refitting. J. Last edited by Heatercathodeshort; 11th Sep 2014 at 8:46 am. |
11th Sep 2014, 3:56 pm | #33 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
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Re: Philco upside down TV.
Hi John,
It turns out that the Westinghouse metal HT rectifier used in the Plessey Mark 1 and 2 chassis is different from the more common type 14A96 which can be found in many mid-fifties TV sets. The Plessey Mark 1 metal rectifier is slightly longer than the the more common one. I'd guess that the reason for this is that the applied AC voltage is higher by 50 volts than the AC/DC mains receivers which operate on a much lower HT voltage, it's typically 190 to 200 volts DC. in those sets. The HT voltage is 250 in the Mark 1 and 2. The metal rectifier in the Mark 1 has three more cooling fins compared with the 14A96. DFWB. |