Regentone TR20 Lacking Width Advice please? Also EHT transformer replacement - UK Vintage Radio Repair and Restoration Discussion Forum

DoctorWho · 7th Jun 2006, 6:16 pm

I have a Regentone TR20 combined radio and TV set which had been partially restored before I bought it, it only remained for me to replace a few old wax condensers for the set to operate well.

It looks as though the mains EHT transformer must have had a problem as the EHT winding has been completely removed and an old tripler from a colour TV (dated 1980) has been connected to the top cap of the EL38.

The set works very well, but it does lack some picture width, this can be increased by increasing the brightness or contrast controls, but this does make the picture too bright and effects the focus.

Would it worth trying a new EL30 to correct this, or do I need to get a new transformer to supply the mains EHT as before and simply mount this alongside the existing transformer? If the latter can anyone suggest where I can find a suitable transformer to supply the required EHT?

I imagine this set to be late 1940's and, as it works so wel, it would be nice to be able to resolve this width issue.

Thanks for any help/advice.

Peter.

brunel · 7th Jun 2006, 7:36 pm

The EHT could be too high using a tripler. I doubt if you will find replacement an EHT Tx.

If you could obtain a doubler just to try. I am not certain, but I believe the Thorn 1500 20" chassis used a doubler.

Regards

Brunel

ppppenguin · 7th Jun 2006, 7:52 pm

The transformer could be rewound though I'm not sure who would do this. Is this a job for Ed Dinning?

Brandenburg make a wide selection of high voltage modules for many applications. I'm sure one could be hidden in the set.

http://www.brandenburg.co.uk/

DoctorWho · 7th Jun 2006, 9:03 pm

That's interesting. I don;t know what voltage the EHT is actually running at as I have no suitable volt meter for such high voltages. From the symptoms I have described do you think replacing the EL38 would be advisable to try? I see from the service data the EHT should be 7kv.

Thanks for the tip abour Brandenberg, am I right to presume that I would need to opt for a 7kv AC output and the rectify this to DC, or do I need a different AC voltage to obtain 7kv DC rectified?

Peter.

ppppenguin · 7th Jun 2006, 9:16 pm

Get a DC supply and forget about the rectifier. Actually you could leave the rectifier in there with a DC supply - it wouldn't make a lot of difference - but you would still need to find power for the heater.

I haven't used one of these Brandenburg modules but I have used other Brandenburg kit in the past and it's all very high quality stuff. Actually far higher quality than you need for a vintage TV. The outputs are very smooth and stable. The only snags I can see with them are that they are not authentic and you need to find a low voltage supply to power them. Might be possible to take that from the heater circuit.

DoctorWho · 7th Jun 2006, 9:46 pm

Thanks Jeffrey. The rectifier valve still has its heater supply intact, it's only the EHT winding which is completely missing. What would you suggest I use as a DC power supply, I have looked at the Brandenberg supplies and they do a 7.5kv unit at a very low current rating. Would you imagine this would be suitable as it's 500v higher than spec?

I did think of mounting a small modern power supply hidden away to power up the Brandenberg unit, that's no problem. I imagine the current required is very minimal, so that should work very well.

I would welcome any other suggestions, but if it is felt that the 7.5KV unit would be adequate then I'll look further in to one of those.

Thanks again,

Peter.

Ed_Dinning · 7th Jun 2006, 9:53 pm

Hi Gent, I'm afraid I don't have the kit for EHT overwind of the flyback variety and its also very difficult to get the silk & enamelled wire. I can do the (leathal) mains derived EHT transformers but only up to 6KV.
It is possible to build your own doubler with pulse caps and colour TV focus rectifiers.
Certainly if the EHT is too high the beam becomes "stiff" and needs more deflection power or gives a narrow picture.

HTH Ed

DoctorWho · 7th Jun 2006, 10:03 pm

Hello Ed,

Thanks for the advice. I think you may have cracked the problem here, from what you have describd I suspect the EHT is probably too high, as the picture is indeed "stiff" and narrow.

Do you have a 6KV transformer available? If so I presume I could just instal one of those besides the original transformer and connect up that way. This would at least return the set to original spec. Also I imagine the picture would be fine on 6KV as there is plenty of "play" on both the brightness and contrast.

If this is not possible does anyone have a double from a colour set available please? I don't have anything like that, and if all else fails it sounds like this would be worth a try.

Thanks again.

Peter.

ppppenguin · 8th Jun 2006, 7:46 am

If you use a Brandenburg module there are several possibilities. The 568 series goes up to 6kV and will probably be the cheapest option. The 3590 goes up to 7.5kV. It looks like all of them have variable output voltage - for the 568 it's simply a matter of varying the input voltage.

DoctorWho · 8th Jun 2006, 12:53 pm

Thanks Jeffrey, I have sent them an enquiry, so we'll see what they come back with.

I have noticed that the EL38 has a blue glow whilst operating, I imagine this may well be due to the extra load the tripler is putting on it. What do others think?

Peter.

7th Jun 2006, 6:16 pm	#1
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Regentone TR20 Lacking Width Advice please? Also EHT transformer replacement I have a Regentone TR20 combined radio and TV set which had been partially restored before I bought it, it only remained for me to replace a few old wax condensers for the set to operate well. It looks as though the mains EHT transformer must have had a problem as the EHT winding has been completely removed and an old tripler from a colour TV (dated 1980) has been connected to the top cap of the EL38. The set works very well, but it does lack some picture width, this can be increased by increasing the brightness or contrast controls, but this does make the picture too bright and effects the focus. Would it worth trying a new EL30 to correct this, or do I need to get a new transformer to supply the mains EHT as before and simply mount this alongside the existing transformer? If the latter can anyone suggest where I can find a suitable transformer to supply the required EHT? I imagine this set to be late 1940's and, as it works so wel, it would be nice to be able to resolve this width issue. Thanks for any help/advice. Peter. Attached Thumbnails

7th Jun 2006, 7:36 pm	#2
brunel Heptode Join Date: Sep 2005 Location: LEEDS.......North of the River Aire. Posts: 872	Re: Regentone TR20 Lacking Width Advice please? The EHT could be too high using a tripler. I doubt if you will find replacement an EHT Tx. If you could obtain a doubler just to try. I am not certain, but I believe the Thorn 1500 20" chassis used a doubler. Regards Brunel

7th Jun 2006, 7:52 pm	#3
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Regentone TR20 Lacking Width Advice please? The transformer could be rewound though I'm not sure who would do this. Is this a job for Ed Dinning? Brandenburg make a wide selection of high voltage modules for many applications. I'm sure one could be hidden in the set. http://www.brandenburg.co.uk/

7th Jun 2006, 9:03 pm	#4
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Regentone TR20 Lacking Width Advice please? That's interesting. I don;t know what voltage the EHT is actually running at as I have no suitable volt meter for such high voltages. From the symptoms I have described do you think replacing the EL38 would be advisable to try? I see from the service data the EHT should be 7kv. Thanks for the tip abour Brandenberg, am I right to presume that I would need to opt for a 7kv AC output and the rectify this to DC, or do I need a different AC voltage to obtain 7kv DC rectified? Peter.

7th Jun 2006, 9:16 pm	#5
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Regentone TR20 Lacking Width Advice please? Get a DC supply and forget about the rectifier. Actually you could leave the rectifier in there with a DC supply - it wouldn't make a lot of difference - but you would still need to find power for the heater. I haven't used one of these Brandenburg modules but I have used other Brandenburg kit in the past and it's all very high quality stuff. Actually far higher quality than you need for a vintage TV. The outputs are very smooth and stable. The only snags I can see with them are that they are not authentic and you need to find a low voltage supply to power them. Might be possible to take that from the heater circuit.

7th Jun 2006, 9:46 pm	#6
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Regentone TR20 Lacking Width Advice please? Thanks Jeffrey. The rectifier valve still has its heater supply intact, it's only the EHT winding which is completely missing. What would you suggest I use as a DC power supply, I have looked at the Brandenberg supplies and they do a 7.5kv unit at a very low current rating. Would you imagine this would be suitable as it's 500v higher than spec? I did think of mounting a small modern power supply hidden away to power up the Brandenberg unit, that's no problem. I imagine the current required is very minimal, so that should work very well. I would welcome any other suggestions, but if it is felt that the 7.5KV unit would be adequate then I'll look further in to one of those. Thanks again, Peter.

7th Jun 2006, 9:53 pm	#7
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,195	Re: Regentone TR20 Lacking Width Advice please? Hi Gent, I'm afraid I don't have the kit for EHT overwind of the flyback variety and its also very difficult to get the silk & enamelled wire. I can do the (leathal) mains derived EHT transformers but only up to 6KV. It is possible to build your own doubler with pulse caps and colour TV focus rectifiers. Certainly if the EHT is too high the beam becomes "stiff" and needs more deflection power or gives a narrow picture. HTH Ed

7th Jun 2006, 10:03 pm	#8
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Regentone TR20 Lacking Width Advice please? Hello Ed, Thanks for the advice. I think you may have cracked the problem here, from what you have describd I suspect the EHT is probably too high, as the picture is indeed "stiff" and narrow. Do you have a 6KV transformer available? If so I presume I could just instal one of those besides the original transformer and connect up that way. This would at least return the set to original spec. Also I imagine the picture would be fine on 6KV as there is plenty of "play" on both the brightness and contrast. If this is not possible does anyone have a double from a colour set available please? I don't have anything like that, and if all else fails it sounds like this would be worth a try. Thanks again. Peter.

8th Jun 2006, 7:46 am	#9
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Regentone TR20 Lacking Width Advice please? If you use a Brandenburg module there are several possibilities. The 568 series goes up to 6kV and will probably be the cheapest option. The 3590 goes up to 7.5kV. It looks like all of them have variable output voltage - for the 568 it's simply a matter of varying the input voltage.

8th Jun 2006, 12:53 pm	#10
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Regentone TR20 Lacking Width Advice please? Thanks Jeffrey, I have sent them an enquiry, so we'll see what they come back with. I have noticed that the EL38 has a blue glow whilst operating, I imagine this may well be due to the extra load the tripler is putting on it. What do others think? Peter.