Making a TV from a scope CRT and other parts - UK Vintage Radio Repair and Restoration Discussion Forum

renato_enca · 23rd Apr 2007, 12:25 am

is it possible to homebrew a TV using some real television valves (PL36 for line output and some supply voltages as done nowadays) and a 3-inch 'scope CRT?

Studio263 · 23rd Apr 2007, 8:24 am

Have a go, how hard can in be?

You won't need the PL36 though, 'scope tubes use electrostatic deflection and so don't need powerful valves like this to drive electromagnetic scan coils.

A good place to start may be to use the small DG7/5 type tube (Servicescope minor etc), this can be deflected with a couple of ECC82's (one for V, one for H) and the HT requirements are well within the range of a pair of normal radio-type transformers (so long as you don't mind the cathode being negative by a couple of hundred volts...)

PM me if you need more help with this, I have a Philips circuit for an oscilloscope that uses the DG7/5 which demonstrates good practice using this tube (and is surprisingly straightforward, odd given the manufacturer!). This could be a good basis for the project.

renato_enca · 23rd Apr 2007, 7:47 pm

Thank you very much for your fast responces. Actually, I have an RCA tube, model 3AQP1, which datasheet says that it needs min. 500Volts, and a maximum of 2750V, for the anode. Is there any risk of X-ray emission using an "EHT" supply of about 2000-2500V? Also, how can I do the timebases using a couple of ECC81's, EF183, PCF802 and similar valves? All I can find on the net is some fancy circuits talking about "phantastron oscillators", using odd-named valves, multitap transformers and 13000 turn iron-powder toroid coils (ok, I'm exaggerating here).

Ed_Dinning · 23rd Apr 2007, 7:58 pm

Hi Renato, no risk of X-rays below about 15KV.
Try and have a look at some of the circuits in other threads on TV's such as the Argus, they had circuits using things like SP61, EF50 and 6SL7 valves and did not use too many components.
Note that the hifger EHT you have the brighter will be the picture, but that greater deflection volts will be required for a full scan of the tube.

Ed

jim_beacon · 23rd Apr 2007, 9:00 pm

The SP41, SP61 and EF50 were all popular valves for sweep generation in the surplus type receivers, though there were often pushed to their limits to do it.

Jim.

renato_enca · 23rd Apr 2007, 9:19 pm

hmm...the EF50 operating voltages look similar to the EF183, which I have some. Can I use it?

jim_beacon · 23rd Apr 2007, 10:14 pm

I wouldn't know - in the design I have (Wireless World surplus televisor), the sweep valves (EF50 or SP61, whatever you have), are run with nearly 500V on the anode. This is well above the rated voltage, but it seemed to work well enough. I think it is a case of try it and see.

Jim.

GMB · 23rd Apr 2007, 11:03 pm

I think the result may be a bit disappointing because scope tubes usually have a longer persistence phosphor than is good for TV and also they are not usually designed with video bandwidth in mind.

Danny · 23rd Apr 2007, 11:07 pm

Hi i built a set using ef80s as the line and frame oscilators and based it on the simplex tv from the television mag. it gave a good picture although it is a drawn curtain set. Danny

renato_enca · 25th Apr 2007, 11:57 pm

hello again
a friend of mine gave me yesterday a real Philips TV black and white CRT tube he had for years, along with the deflection coils. I designed and build a PCF805/PL36 line output stage, and then experimented the stage with an HR8029 modern LOPT. The 15kHz pitch can be heard well, but there's very low boosted voltages/eht. Is it necessary to use an old valve-designed LOPT, or can I use modern LOPT's?

23rd Apr 2007, 12:25 am	#1
renato_enca Retired Dormant Member Join Date: Feb 2007 Location: Lisbon, Portugal Posts: 51	Making a TV from a scope CRT and other parts is it possible to homebrew a TV using some real television valves (PL36 for line output and some supply voltages as done nowadays) and a 3-inch 'scope CRT?

23rd Apr 2007, 8:24 am	#2
Studio263 Octode Join Date: Apr 2007 Location: Hampshire, UK. Posts: 1,577	Re: 'scope CRT television - is it possible? Have a go, how hard can in be? You won't need the PL36 though, 'scope tubes use electrostatic deflection and so don't need powerful valves like this to drive electromagnetic scan coils. A good place to start may be to use the small DG7/5 type tube (Servicescope minor etc), this can be deflected with a couple of ECC82's (one for V, one for H) and the HT requirements are well within the range of a pair of normal radio-type transformers (so long as you don't mind the cathode being negative by a couple of hundred volts...) PM me if you need more help with this, I have a Philips circuit for an oscilloscope that uses the DG7/5 which demonstrates good practice using this tube (and is surprisingly straightforward, odd given the manufacturer!). This could be a good basis for the project.

23rd Apr 2007, 7:47 pm	#3
renato_enca Retired Dormant Member Join Date: Feb 2007 Location: Lisbon, Portugal Posts: 51	Re: 'scope CRT television - is it possible? Thank you very much for your fast responces. Actually, I have an RCA tube, model 3AQP1, which datasheet says that it needs min. 500Volts, and a maximum of 2750V, for the anode. Is there any risk of X-ray emission using an "EHT" supply of about 2000-2500V? Also, how can I do the timebases using a couple of ECC81's, EF183, PCF802 and similar valves? All I can find on the net is some fancy circuits talking about "phantastron oscillators", using odd-named valves, multitap transformers and 13000 turn iron-powder toroid coils (ok, I'm exaggerating here).

23rd Apr 2007, 7:58 pm	#4
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,195	Re: 'scope CRT television - is it possible? Hi Renato, no risk of X-rays below about 15KV. Try and have a look at some of the circuits in other threads on TV's such as the Argus, they had circuits using things like SP61, EF50 and 6SL7 valves and did not use too many components. Note that the hifger EHT you have the brighter will be the picture, but that greater deflection volts will be required for a full scan of the tube. Ed

23rd Apr 2007, 9:00 pm	#5
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: 'scope CRT television - is it possible? The SP41, SP61 and EF50 were all popular valves for sweep generation in the surplus type receivers, though there were often pushed to their limits to do it. Jim.

23rd Apr 2007, 9:19 pm	#6
renato_enca Retired Dormant Member Join Date: Feb 2007 Location: Lisbon, Portugal Posts: 51	Re: 'scope CRT television - is it possible? hmm...the EF50 operating voltages look similar to the EF183, which I have some. Can I use it?

23rd Apr 2007, 10:14 pm	#7
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: 'scope CRT television - is it possible? I wouldn't know - in the design I have (Wireless World surplus televisor), the sweep valves (EF50 or SP61, whatever you have), are run with nearly 500V on the anode. This is well above the rated voltage, but it seemed to work well enough. I think it is a case of try it and see. Jim.

23rd Apr 2007, 11:03 pm	#8
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,099	Re: 'scope CRT television - is it possible? I think the result may be a bit disappointing because scope tubes usually have a longer persistence phosphor than is good for TV and also they are not usually designed with video bandwidth in mind.

23rd Apr 2007, 11:07 pm	#9
Danny Heptode Join Date: Jul 2003 Location: North Walsham, Norfolk, UK. Posts: 516	Re: 'scope CRT television - is it possible? Hi i built a set using ef80s as the line and frame oscilators and based it on the simplex tv from the television mag. it gave a good picture although it is a drawn curtain set. Danny

25th Apr 2007, 11:57 pm	#10
renato_enca Retired Dormant Member Join Date: Feb 2007 Location: Lisbon, Portugal Posts: 51	Re: 'scope CRT television - is it possible? hello again a friend of mine gave me yesterday a real Philips TV black and white CRT tube he had for years, along with the deflection coils. I designed and build a PCF805/PL36 line output stage, and then experimented the stage with an HR8029 modern LOPT. The 15kHz pitch can be heard well, but there's very low boosted voltages/eht. Is it necessary to use an old valve-designed LOPT, or can I use modern LOPT's?