Unusual frame timebase circuits. - UK Vintage Radio Repair and Restoration Discussion Forum

FERNSEH · 6th Feb 2008, 1:47 pm

In my notes about the Baird T23 TV set I mentioned that the frame timebase employs a single valve, the circuit serves as a power oscillator.

Two post war TV receivers employ a single valve in the frame timebase. One is the Ambassador TV2. In this set the scanning coils include the oscillator primary and feedback windings. An additional winding backs off the magnetic field caused by the DC current through the primary. The FTB in the Ambassador employs a Mazda 20P1. A valve which one would consider to powerful for this application.
The other set which employs a similar circuit is the strange Murphy V136. In that set the valve is a Mazda 6F14, a valve intended for use as a video amplifier.

DFWB.

beery · 6th Feb 2008, 7:48 pm

Hi all,
here is the line and frame timebase circuit for the Baird T5/T23.
The frame timebase is on the right of the circuit and the frame coils are shown connected via an octal connector.

https://www.vintage-radio.net/forum/...2&d=1152616423

Cheers.
Andy

FERNSEH · 6th Feb 2008, 9:43 pm

Hi Andy,
You beat me to it, I was going to post the circuit diagram of the T23 later today.
The only difference between the timebase circuits of the two sets is that later T23 incorporates an interlace diode. This can be a 2D4A double diode or a Mazda AC/HL2 connected as a diode.

DFWB.

FERNSEH · 6th Feb 2008, 10:54 pm

The German E1 receiver employs a single valve frame timebase. The circuit diagram appears on the ETF website. The valve a special type, the ES111.

http://www.earlytelevision.org/e1_schematic.html

It could be that the frame circuit was a contribution from Fernseh AG, a firm that was associated with Baird Television in the early thirties.

DFWB.

Heatercathodeshort · 10th Feb 2008, 10:38 am

Hello David,
It never fails to amaze me how simple the timebase circuits can be in vintage receivers. The madness appears to come up for breath in circuits such as the Murphy V136 that you mention. The crazy idea at the time was to save a valve in the circuit but Murphy then used TWO expensive 6P28's in the line output stage, totally unnecessary as all other makers used one.
The gas Thyratrons such as the Mazda T41 and 6K25 were used into the early 50's by Ultra and others and worked quite well but as the valves aged they tended to go unstable. Very few components were used in the circuit and the replacement of the occasional valve was simple and quick.
The Bush T91 and TV1 used the Mullard EN31 in both frame and line generators but I believe this was the only application of the Mullard Thyratron in post war receivers. J.

6th Feb 2008, 1:47 pm	#1
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Unusual frame timebase circuits. In my notes about the Baird T23 TV set I mentioned that the frame timebase employs a single valve, the circuit serves as a power oscillator. Two post war TV receivers employ a single valve in the frame timebase. One is the Ambassador TV2. In this set the scanning coils include the oscillator primary and feedback windings. An additional winding backs off the magnetic field caused by the DC current through the primary. The FTB in the Ambassador employs a Mazda 20P1. A valve which one would consider to powerful for this application. The other set which employs a similar circuit is the strange Murphy V136. In that set the valve is a Mazda 6F14, a valve intended for use as a video amplifier. DFWB. Attached Thumbnails

6th Feb 2008, 7:48 pm	#2
beery Heptode Join Date: Jun 2006 Location: Ware, Hertfordshire, UK. Posts: 988	Re: Unusual frame timebase circuits. Hi all, here is the line and frame timebase circuit for the Baird T5/T23. The frame timebase is on the right of the circuit and the frame coils are shown connected via an octal connector. https://www.vintage-radio.net/forum/...2&d=1152616423 Cheers. Andy Last edited by beery; 6th Feb 2008 at 7:49 pm. Reason: spelling

6th Feb 2008, 9:43 pm	#3
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Unusual frame timebase circuits. Hi Andy, You beat me to it, I was going to post the circuit diagram of the T23 later today. The only difference between the timebase circuits of the two sets is that later T23 incorporates an interlace diode. This can be a 2D4A double diode or a Mazda AC/HL2 connected as a diode. DFWB.

6th Feb 2008, 10:54 pm	#4
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Unusual frame timebase circuits. The German E1 receiver employs a single valve frame timebase. The circuit diagram appears on the ETF website. The valve a special type, the ES111. http://www.earlytelevision.org/e1_schematic.html It could be that the frame circuit was a contribution from Fernseh AG, a firm that was associated with Baird Television in the early thirties. DFWB.

10th Feb 2008, 10:38 am	#5
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Unusual frame timebase circuits. Hello David, It never fails to amaze me how simple the timebase circuits can be in vintage receivers. The madness appears to come up for breath in circuits such as the Murphy V136 that you mention. The crazy idea at the time was to save a valve in the circuit but Murphy then used TWO expensive 6P28's in the line output stage, totally unnecessary as all other makers used one. The gas Thyratrons such as the Mazda T41 and 6K25 were used into the early 50's by Ultra and others and worked quite well but as the valves aged they tended to go unstable. Very few components were used in the circuit and the replacement of the occasional valve was simple and quick. The Bush T91 and TV1 used the Mullard EN31 in both frame and line generators but I believe this was the only application of the Mullard Thyratron in post war receivers. J.