Dynatron TV27 "Fulmer"

I can confirm that the CRT is definitely faulty, nothing can be done to save it.

The replacement tube is to be a 17BP4A.  This tube has a tetrode gun so provision for the supply voltage for the first anode will be made.  The replacement tube has an ion trap.

Till Eulenspiegel.

You covered every possibility, nothing more you could have done. We have said before it’s going to be the lack of CRT’s that stop repair of old TV’s.

What make is the 17BP4A, more like a USA number?

Hi Frank, The 17BP4A tube was taken out of a French HMV TV set. La Voix de Son Maitre.  It is one of those projects that might never get done so the tube can be put to better use in the Dynatron. 

The tube was most likely imported from America just like some Emitron CRTs were.

Till Eulenspiegel.

Thanks, "Till", am sure many might have just abandoned it, but so much work has gone into it that wouldn't seem right.  It's also the first 405 line set that started my collection so it's symbolic to me. (hard one to start on!!)  I reckon it was also one of the first sets in the North East and when it was new could only have received a signal from Channel 2 Holme Moss, which was how it was configured (there's an M for Manchester stamped on the back of the chassis).  I know a bit about the previous owner, quite a character by the look of it, he had a Rolls Royce with a personal plate and lived in Morpeth, but Low Fell originally when the set was new, wonder if he could really have received pictures on Channel 2.  It looks like the set may have been abandoned in 1955 according to the repair ticket, also the time ITV came in of course.

According to the coverage maps for Holme Moss Channel 2, Northallerton is on the edge of the 1 mV/m and Durham is outside of the 100 microV/m area but still in the shaded area classed as fringe.

Morpeth is a lot further north but reception was probably possible if not very consistent.

@nuvistor

Thanks, I think he may have had the set at Low Fell Gateshead for the first year or two, as I understand it we got our own transmitter from May 1953  but this set probably predates that.  Clearly the very first TVs in this area could only have received from Holme Moss if at all possible and single channel sets from this era that have not been converted do often show as Channel 2.  What I'm not clear on is which channel number we used from 1953?  No doubt someone will know, maybe it was 2 after all.  Quite a bit before my time 🙂 

Presume it would be Pontop Pike on ch 5, MOSI in CastleFields Manchester have one end of the microwave link from Holme Moss to Pontop Pike including the large dish aerial. Not sure but presume there was more than one hop.

Interesting history on the link and then on north to Kirk O’Shotts, it’s on the web, must see if I can find it.

Nice potted history of the early BBC network.

http://wiki.scotlandonair.com/index.php?title=History_of_BBC_television_distribution

Hi Frank,   Here in the North-East of England a high performance TV receiver like the Dynatron "Fulmar" would have received the Holme Moss transmitter.  But did this set actually receive the Holme Moss transmitter?  The Pontop Pike low power transmitter was ready to transmit the Queen's coronation in June 1953.  When did the channel 5 station commence test transmissions, late 1952? the same year the Dynatron TV was on sale.    

 It's a pity that the Brimar CRT can't be saved because much of the design of this set can be attributed to STC.  The STC Magna-View circuits are very similar to those in the TV27A.  There is an additional RF amplifier stage and the sound IF amplifier has two stages.  Sound output valve is a 6BW6.  That strange sync separator in not used in the Dynatron although it was considered during the early stages of the restoration.  

Til Eulenspiegel.

Hi David,

Thanks for the information.

There were sets around South Lancashire that received Sutton Coldfield on ch 4 at 50 microV/m, no idea how good the picture was though. A friend of mine, his father got some compensation for an injury and remembers him buying a TV and large aerial to receive Sutton Coldfield, around 1950. He is a similar age to me and doesn’t remember the picture quality but his dad was happy with it. Another 3 years and he could have bought a set to receive Holme Moss with a strong signal.

Thanks for the info both of you.  That is what I wanted to know, I had a feeling that it was Channel 5 but thought that only came in later in the days of ITV and the turret tuner.  When I first got the set working I could not get anything through the front end and wasn't sure what channel it would be tuned to.  I had a Pineapple converter (with a Channel 1 modulator added).  Someone told me the set might be Channel 5 so had a modulator specially made (by Dinosaur), they were a little puzzled as to why anyone would want a Channel 5 modulator and said no one had ever asked for one.  I too was confused as Channel 5 was supposedly "Wenvoe" (Wales).  I still couldn't get anything on the set with that modulator and later came to the conclusion it was Channel 2.  I used the set by putting the signals into the demodulator stages, though it is possible the front end needed further repair rather than not having the right modulator (this was my first set remember so I had little experience).  When I got a combined converter/modulator I sold the Dinosaur, shame as it was the only one they ever made, and I could do with it now as modulators seem to be hard to find, I need one to enable a Pineapple to be used as a second converter since its built in modulator failed.  Life is so much easier now with our more recent generation of converters/modulators!

The replacement CRT is a Mazda "Cathoscope" type 17BP4C.  This one was made most likely in France.

Till Eulenspiegel.

Fitted the replacement tube today.  Can't display any pictures on the screen because the set has developed a fault in the frame timebase.  Refer to post No.8 for the circuit diagram.  The frame output transformer is supplied with boosted HT via a 10Kohm resistor from the line output transformer.  This component has burnt out.   The ECL80 taken out and the frame output transformer has been disconnected.  Seems that the insulation has broken down somewhere.  Possibly on the srbp component group board.

Till Eulenspiegel.

The insulation between pin 5 and 6 of the valveholder has broken down. It will be replaced today.

Till Eulenspiegel.

Thankfully doesn't sound too serious if that is all it is, let's hope it's not going to be too difficult, there are other sets in the pipeline as you know 🙂   This set appears a little jinxed, after all that work it's still not always been possible to watch decent images for any length of time, just on the odd occasion was it reliable for hours, but when it was it was superb of course.

The replacement valveholder is now fully wired up and the frame timebase  returned to working order.  

The "new" CRT displays a good bright picture.  The existing focus control works well with the tetrode tube. I was concerned that the old triode tube might have needed a stronger focussing field than the tetrode tube. But no problems the focus magnet  works OK. 

Just few jobs to do the set before it's signed off.

Till Eulenspiegel.

Smashing, looks good.

  All working fine now thanks for your efforts especially the last visit, Sky News doesn't seem appropriate somehow but it is what was showing at the time.

Hi Derren, one extra refinement worth considering is frame flyback suppression. On light scenes the frame sync pulses are noticeable.  As the frame flyback is rapid the negative going pulse from the oscillator will have little suppression effect. A pulse stretcher is needed.  This can be effected by using a monostable oscillator.    The set was made in 1952 and the rules are we must utilise the tech of the time.  No 555 timers!  

Till Eulenspiegel.

Well it's super, been on for a couple of hours the last couple of nights.  Yes the flyback lines have been a problem in the past, even with its original transformer, but I now find I can get rid of them by adjusting the sensitivity/contrast/brightness and it is now not a problem.  If you want me to make a tiny criticism it would be of the width, it's not quite as full as it should be, depends on the picture content (and format of course), but it is often just a millimetre or two short in the centre edge for some reason.  I would have thought ideally it should scan right around the side of the tube.  Bearing in mind the house voltage is often a bit lower than it should be I have thought that stepping up the voltage selector by 10 volts might sort it, but it seems a shame to put stress on all of the components in that way.  Either way I would say it's better than it's ever been.