UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

space_charged · 6th Mar 2018, 5:54 pm

Thanks dazzlevision for your tips.

I remember being surprised that it was partly transistorised, which I could see from the circuit diagram that was provided with the set. Our set was branded "Alba".

Yes you are SO right about the LOPT. We rented our set and when it died the local TV shop (based in Morningside) sent a service man. I could hear 15.626Kcs in those days so I knew the line stage wasn't running. There was an all too familiar smell of something getting hotter than it should. The service engineer poked about and as he did I could hear the familiar high frequency of the line stage reappearing. He (correctly) diagnosed a dry on the line hold pot, because the oscillator came and went as he moved the pot spindle.

We chatted about the fault and he became rapidly surprised that this little boy (14) knew lots about TVs and line stages in particular; always my favourite bit of a telly.

He seemed in no great hurry to switch the set off, though the oscillator wasn't running. I made some casual remark about it not really being such a good idea leaving a large pentode with no grid drive for any length of time.

At length he got round to switching it off and re-soldering the dry joint. The set worked fine after that, but NOT for long. It failed that evening and the service engineer had to called again. This time the diagnosis was an o/c LOPT primary - he he. Possibly (I love to think so) due to the over current caused by the LOV with no grid drive.

A new LOPT was fitted, but the TV had to go back to repair shop and was away for a week or two. The set was returned but very badly set up. The width and height were wrong. The family decided to go for a colour set, the Bush/Rank/Murphy one so the G23T210 went back to the rental shop. The BRM colour set was all transistor, except for the CRT.

I'll take care to dry the LOPT before I try to run it. In the past, I've done that by removing the LOPT and putting it on a central heating radiator for a month! In fact, I have one from a 17TG100U on a radiator right now. Another approach is to pass a (current limited) current through the primary to help drive off any moisture.

LOPTs can be re-wound. As they run at high frequency, the number of turns is relatively low (compared to 50Hz transformers) and the wire thick enough to handle more easily.

The overwind is a different matter, but that could be done on a winding machine, or an overwind from a donor set used. Alternatively a tripler connected to the LOV anode...

Chas

6th Mar 2018, 5:54 pm	#3
space_charged Hexode Join Date: Dec 2014 Location: West Midlands, UK. Posts: 315	Re: Philips G23T210A Thanks dazzlevision for your tips. I remember being surprised that it was partly transistorised, which I could see from the circuit diagram that was provided with the set. Our set was branded "Alba". Yes you are SO right about the LOPT. We rented our set and when it died the local TV shop (based in Morningside) sent a service man. I could hear 15.626Kcs in those days so I knew the line stage wasn't running. There was an all too familiar smell of something getting hotter than it should. The service engineer poked about and as he did I could hear the familiar high frequency of the line stage reappearing. He (correctly) diagnosed a dry on the line hold pot, because the oscillator came and went as he moved the pot spindle. We chatted about the fault and he became rapidly surprised that this little boy (14) knew lots about TVs and line stages in particular; always my favourite bit of a telly. He seemed in no great hurry to switch the set off, though the oscillator wasn't running. I made some casual remark about it not really being such a good idea leaving a large pentode with no grid drive for any length of time. At length he got round to switching it off and re-soldering the dry joint. The set worked fine after that, but NOT for long. It failed that evening and the service engineer had to called again. This time the diagnosis was an o/c LOPT primary - he he. Possibly (I love to think so) due to the over current caused by the LOV with no grid drive. A new LOPT was fitted, but the TV had to go back to repair shop and was away for a week or two. The set was returned but very badly set up. The width and height were wrong. The family decided to go for a colour set, the Bush/Rank/Murphy one so the G23T210 went back to the rental shop. The BRM colour set was all transistor, except for the CRT. I'll take care to dry the LOPT before I try to run it. In the past, I've done that by removing the LOPT and putting it on a central heating radiator for a month! In fact, I have one from a 17TG100U on a radiator right now. Another approach is to pass a (current limited) current through the primary to help drive off any moisture. LOPTs can be re-wound. As they run at high frequency, the number of turns is relatively low (compared to 50Hz transformers) and the wire thick enough to handle more easily. The overwind is a different matter, but that could be done on a winding machine, or an overwind from a donor set used. Alternatively a tripler connected to the LOV anode... Chas