Valves for a CRT Televisor - UK Vintage Radio Repair and Restoration Discussion Forum

Sam · 20th Dec 2005, 2:50 pm

I thought best to put this here as it is a general query on circuitry, as opposed to a definite TV question.

I have found a circuit for a CRT-display 30-line televisor in a book I got out of the University Library (Television, Theory and Practice; J. H. Reyner; Chapman and Hall, 1934) but want to adapt the circuit to use valve-types that I have.

The circuit calls for 2xGDT, 1xMVSPen, 1xMSPen and 2xMHL. Looking at the circuit, the GDTs are Thyratrons, and used to generate the line and frame timebases. These I can sub 6K25s or GT1Cs for. The MVSPen and MSPen appear to be constant-current valves used to improve the linearity. The circuitry here confuses me a bit. The name implies they are pentodes, but there are only two grids drawn in the circuit (tetrodes). I assume this means the supressor grid connected to the cathode has not been drawn as it is all done internally, or am I wrong?

The little information I have been able to find implies these are HF/IF valves. Is it ok then to substitute 6K7Gs or similar, so long as they can handle sufficient anode current, or should I use audio O/P or line O/P valves? The books I have seem to give little information on constant-current pentodes. The MHL triodes are used in the detector stage of the reciever, so I don't really need to include these.

I want to try and use shouldered valves as they will look 'right' for a mid- to late-30s circuit!

I am sucumbing to a bit of form over function!

Sam

Neil Breward · 20th Dec 2005, 4:22 pm

Hi - this sounds a fascinating project! You could probably use a 6K7G or EF39 as a substitute for the MVSPen as they are vari-mu pentodes, but both are really 1940s valves and Octals. Why not go for a VP4B and SP4B (for the MSPen), both British 7-pin jobs and more authentically 1935?

Good luck!

Cheers,
Neil

Dave Moll · 20th Dec 2005, 5:44 pm

This sounds an novel idea. I've not heard of anyone doing this - though that's probably down to my ignorance.

I assume that this is planned to be a single-standard set, but wonder how difficult it would be to adapt it to dual standard to work also on the NBTVA 32-line standard in the way that Gary Millard's NBTV Viewer software does.

Panrock · 20th Dec 2005, 6:07 pm

Quote:

Originally Posted by Dave Moll

I assume that this is planned to be a single-standard set, but wonder how difficult it would be to adapt it to dual standard to work also on the NBTVA 32-line standard in the way that Gary Millard's NBTV Viewer software does.

If it's a CRT set presumably just a tweak on the line hold ?

Out of interest which type of CRT are you using Sam?

Steve

jim_beacon · 20th Dec 2005, 7:18 pm

Sam,

you could try the SP41 or SP61, these were used in a number of pre-war designs, but are readily available as the RAF VR65 and VR65A.

The SP41 / VR65A has a 4V heater, and the SP61 / VR65 has a 6.3V heater.

Jim.

Sam · 21st Dec 2005, 12:14 am

Quote:

Originally Posted by Panrock

If it's a CRT set presumably just a tweak on the line hold ?

Out of interest which type of CRT are you using Sam?

From what it says in the text it does sound as if adjusting a control between the line and frame timebases can cause a line or two more or less than 30 to display - I think this is because the black-band synchronising used by Baird only was a line, and not a frame, synchronising signal.

The CRT will be a later type - probably an oscilloscope tube. I have a couple of 3" ones. I am trying to use this as a way to put some of the cr*p I have to use!

Quote:

Originally Posted by Neil Breward

You could probably use a 6K7G or EF39 as a substitute for the MVSPen as they are vari-mu pentodes, but both are really 1940s valves and Octals. Why not go for a VP4B and SP4B (for the MSPen), both British 7-pin jobs and more authentically 1935?

I was trying to use valves I have as I only have a few pre-octal types. I do have one SP4B, but I have several 6K7Gs. I can't remember, but I think I have an SP46 or 61 about!

It will be better to keep all the heater voltages the same too.

I will get the circuit scanned and attached tomorrow.

Sam

Sam · 22nd Dec 2005, 4:57 pm

OK, here is the circuit. Looks a lot simpler than a 405-line set!

Sam

20th Dec 2005, 2:50 pm	#1
Sam Hexode Join Date: Apr 2003 Location: Higham-on-the-Hill, Leicestershire, UK. Posts: 338	Valves for a CRT Televisor I thought best to put this here as it is a general query on circuitry, as opposed to a definite TV question. I have found a circuit for a CRT-display 30-line televisor in a book I got out of the University Library (Television, Theory and Practice; J. H. Reyner; Chapman and Hall, 1934) but want to adapt the circuit to use valve-types that I have. The circuit calls for 2xGDT, 1xMVSPen, 1xMSPen and 2xMHL. Looking at the circuit, the GDTs are Thyratrons, and used to generate the line and frame timebases. These I can sub 6K25s or GT1Cs for. The MVSPen and MSPen appear to be constant-current valves used to improve the linearity. The circuitry here confuses me a bit. The name implies they are pentodes, but there are only two grids drawn in the circuit (tetrodes). I assume this means the supressor grid connected to the cathode has not been drawn as it is all done internally, or am I wrong? The little information I have been able to find implies these are HF/IF valves. Is it ok then to substitute 6K7Gs or similar, so long as they can handle sufficient anode current, or should I use audio O/P or line O/P valves? The books I have seem to give little information on constant-current pentodes. The MHL triodes are used in the detector stage of the reciever, so I don't really need to include these. I want to try and use shouldered valves as they will look 'right' for a mid- to late-30s circuit! I am sucumbing to a bit of form over function! Sam __________________ Can he lead a Normal life, Doctor? No, he will be ... an Engineer.

20th Dec 2005, 4:22 pm	#2
Neil Breward Retired Dormant Member Join Date: Aug 2005 Location: Keyworth nr. Nottingham, UK Posts: 140	Re: Valves for a CRT Televisor Hi - this sounds a fascinating project! You could probably use a 6K7G or EF39 as a substitute for the MVSPen as they are vari-mu pentodes, but both are really 1940s valves and Octals. Why not go for a VP4B and SP4B (for the MSPen), both British 7-pin jobs and more authentically 1935? Good luck! Cheers, Neil

20th Dec 2005, 5:44 pm	#3
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,127	Re: Valves for a CRT Televisor This sounds an novel idea. I've not heard of anyone doing this - though that's probably down to my ignorance. I assume that this is planned to be a single-standard set, but wonder how difficult it would be to adapt it to dual standard to work also on the NBTVA 32-line standard in the way that Gary Millard's NBTV Viewer software does.

20th Dec 2005, 7:18 pm	#5
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: Valves for a CRT Televisor Sam, you could try the SP41 or SP61, these were used in a number of pre-war designs, but are readily available as the RAF VR65 and VR65A. The SP41 / VR65A has a 4V heater, and the SP61 / VR65 has a 6.3V heater. Jim.

22nd Dec 2005, 4:57 pm	#7
Sam Hexode Join Date: Apr 2003 Location: Higham-on-the-Hill, Leicestershire, UK. Posts: 338	Re: Valves for a CRT Televisor OK, here is the circuit. Looks a lot simpler than a 405-line set! Sam Attached Thumbnails __________________ Can he lead a Normal life, Doctor? No, he will be ... an Engineer.