TV24 EHT questions - UK Vintage Radio Repair and Restoration Discussion Forum

dominicbeesley · 3rd Feb 2008, 10:51 pm

I was going to have a go at stripping down and resealing the LOPTx today as discussed in the LOPT Saturation thread started by Heatercathodeshort.

Before starting I decided I'd make a HV probe and give the set one more chance to prove itself before this drastic surgery. Much to my surprise its worked faultlessly since the Rugby finished this afternoon without a hint of fade. EHT staying between 8.5KV (testcard) 8-10Kv (off air) and 11 KV (no signal).

Previously watching off air programs the picture would gradually get darker and darker over the course of about and hour or so.

Could this be because the set has had a chance to "dry out" being in a nice warm living room for about 3 months near a radiator and coal fire? Previously had been in a slightly damp worshop.

Any ideas?

Dom

Steve_P · 3rd Feb 2008, 10:58 pm

Possibly, yeah. Keep with it and see what happens. I had a Bush TV125 'repair' itself similarly 2 years back.

Cheers,

Steve P.

jooles405 · 12th Feb 2008, 11:41 pm

I was interested to see the reference to a TV125 LOPT - I have a TV125 which exhibits simialr problmes - the A1 and EHT are fine after switch on (and warm up) but then over the next five minutes or so the levels drop and the raster fades. If left on the overwind leg of the transformer over heats with a sizzle and smell of molten pitch at which point I hastily switched off.

After cooling down the set works again as before. Any ideas if or how this can be fixed?

Steve_P · 12th Feb 2008, 11:49 pm

This is what I call 'Bush LOPT disease'. It was common, and Rank LOPTs were sold by the hundred. The EHT overwind tends to Overheat, and when it does, the EHT falls away.

Ways to fix it:

1: Another LOPT.
2: Fit a tripler.
3: This idea - mod at the bottom of the page!
4: Have it rewound - Ed Dinning or MurphyMad do them.

Cheers,

Steve P

https://www.vintage-radio.net/forum/...ush+TV125+LOPT

dominicbeesley · 13th Feb 2008, 9:47 am

Or after mine and Heatercathodeshort's in the other thread https://www.vintage-radio.net/forum/...ad.php?t=24655 maybe just

5: try taking it out and giving it a long bake in an oven
6: "reflow" the pitch

Got to be worth a try

Dom

jooles405 · 14th Feb 2008, 1:37 pm

Thanks for the suggestions and the link. This stacks up with what I was thinking and I am in the process of removing the LOPT - rusted bolts in the grommet mounts are causing much frustration at the present time.

I'll try the hairdryer approach in-situ while the WD40 is working on the rusted bolts. I'll report back in a day or two.

3rd Feb 2008, 10:51 pm	#1
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	TV24 EHT questions I was going to have a go at stripping down and resealing the LOPTx today as discussed in the LOPT Saturation thread started by Heatercathodeshort. Before starting I decided I'd make a HV probe and give the set one more chance to prove itself before this drastic surgery. Much to my surprise its worked faultlessly since the Rugby finished this afternoon without a hint of fade. EHT staying between 8.5KV (testcard) 8-10Kv (off air) and 11 KV (no signal). Previously watching off air programs the picture would gradually get darker and darker over the course of about and hour or so. Could this be because the set has had a chance to "dry out" being in a nice warm living room for about 3 months near a radiator and coal fire? Previously had been in a slightly damp worshop. Any ideas? Dom

3rd Feb 2008, 10:58 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: TV24 EHT questions Possibly, yeah. Keep with it and see what happens. I had a Bush TV125 'repair' itself similarly 2 years back. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

12th Feb 2008, 11:41 pm	#3
jooles405 Triode Join Date: Jul 2007 Location: Buckden, Skipton, North Yorkshire, UK. Posts: 34	Re: TV24 EHT questions I was interested to see the reference to a TV125 LOPT - I have a TV125 which exhibits simialr problmes - the A1 and EHT are fine after switch on (and warm up) but then over the next five minutes or so the levels drop and the raster fades. If left on the overwind leg of the transformer over heats with a sizzle and smell of molten pitch at which point I hastily switched off. After cooling down the set works again as before. Any ideas if or how this can be fixed? __________________ Julian, Buckden, Skipton, North Yorkshire

12th Feb 2008, 11:49 pm	#4
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: TV24 EHT questions This is what I call 'Bush LOPT disease'. It was common, and Rank LOPTs were sold by the hundred. The EHT overwind tends to Overheat, and when it does, the EHT falls away. Ways to fix it: 1: Another LOPT. 2: Fit a tripler. 3: This idea - mod at the bottom of the page! 4: Have it rewound - Ed Dinning or MurphyMad do them. Cheers, Steve P https://www.vintage-radio.net/forum/...ush+TV125+LOPT __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

13th Feb 2008, 9:47 am	#5
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: TV24 EHT questions Or after mine and Heatercathodeshort's in the other thread https://www.vintage-radio.net/forum/...ad.php?t=24655 maybe just 5: try taking it out and giving it a long bake in an oven 6: "reflow" the pitch Got to be worth a try Dom Last edited by dominicbeesley; 13th Feb 2008 at 9:57 am.

14th Feb 2008, 1:37 pm	#6
jooles405 Triode Join Date: Jul 2007 Location: Buckden, Skipton, North Yorkshire, UK. Posts: 34	Re: TV24 EHT questions Thanks for the suggestions and the link. This stacks up with what I was thinking and I am in the process of removing the LOPT - rusted bolts in the grommet mounts are causing much frustration at the present time. I'll try the hairdryer approach in-situ while the WD40 is working on the rusted bolts. I'll report back in a day or two. __________________ Julian, Buckden, Skipton, North Yorkshire