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Dynatron TV27 "Fulmar"

 
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Re: Dynatron TV27 "Fulmar"

Post by Cathovisor » Wed Sep 09, 2015 11:05 am

The remaining values would be instructive on that circuit.

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Wed Sep 09, 2015 6:37 pm

Revised circuit with component values.

Till Eulenspiegel.
Attachments
000_0340.jpg

 
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Re: Dynatron TV27 "Fulmar"

Post by Cathovisor » Wed Sep 09, 2015 10:55 pm

Thanks for that - there are some long time constants involved there, are there not...?

 
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Re: Dynatron TV27 "Fulmar"

Post by Derren » Thu Sep 10, 2015 3:06 pm

The plot thickens! Am beginning to think I wasn't being such a fool after all putting the signal in at the detector stages :) Have now located some decent data sent to me by Tudor Gwilliam Rees many years ago, in the absence of anything on the TV27 he sent me some TV29 stuff (just as hard to find am sure!). This set is quite different in that it uses EF80s not 6AM6 and the CRT is an MW53-80. It does however employ EB91s (6AL5) and ECC82 (12AT7). There's a comprehensive circuit description and even scope readings! (if only we had this for this one!) It describes the EB91s as flywheel sync and AGC, the ECC82 black spotter/cathode follower. Might be worth me bringing this over?

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Thu Sep 10, 2015 3:43 pm

News Flash! Well it turns out the strange circuit is as Derren speculated indeed is a white spot eliminator, the control panel calls it a "black spotter". The cathode of the left hand side triode is returned to chassis through a 25Kohm variable resistor. That part has now been replaced, but before the control panel is refitted the contrast control must be replaced.

We know that the model TV30 was the first Dynatron TV to employ the Ekco chassis. I've never seen the TV29, that might possibly have been the 13 channel set which was a pure Dynatron design.

Then there was the strange TV32 which employed elements of both Ekco and Dynatron design cues.
http://www.vintage-radio.net/forum/show ... atron+TV32

Till Eulenspiegel.

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Thu Sep 10, 2015 4:43 pm

That's the control panel refitted. The black spotter control does work, clipping the peak whites. With regard to those long time constant circuits they certainly do filter out any video component but do they have to be so long? The contrast control is now functional. The original 10Kohm variable resistance was OC at one end so the result was no proper control of the contrast, just all or nothing at all.

Till Eulenspiegel.

 
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Re: Dynatron TV27 "Fulmar"

Post by Derren » Thu Sep 10, 2015 4:52 pm

Excellent, and what a great idea that front panel is, I've certainly not seen another like it, how wonderful to be able to adjust frame hold, line hold, width, height, sensitivity, linearity etc all from the front without having to reach behind the set! If the front panel still functions and the signal now goes into the aerial and the contrast control works I'll be very happy! (preferably with a nice loud line whistle too :) )

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Thu Sep 10, 2015 6:43 pm

The attachment shows I'm getting real results at last but I need to squeeze more width from the line output stage. All the signals are now inputted through the aerial socket. A few more tweeks carried out today has resulted in even more gain from the RF amplifier, in fact the sensitivity control is now turned well down on order that the new contrast control can operate correctly. The set can easily overload with the signals from the Aurora.
So to sum up more width and height, a retrim of the IFs again and that's it,
The anode of the ECL80 frame output pentode was supplied from the boosted HT line, at present I'm supplying the ECL80 from the 205 volt HT supply. In the original circuit the boost HT might not have been as high as it is now, it is 370 volts. It's likely the HT for the anode of the ECL80 should be 250 volts, but no more.

Till Eulenspiegel.
Attachments
000_0342.jpg

 
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Re: Dynatron TV27 "Fulmar"

Post by crustytv » Thu Sep 10, 2015 6:58 pm

Hi David,

The quality of the TC looks outstanding, superb work :aad

This thread is undoubtedly one of most interesting to follow and has had me checking in daily if not hourly. Following your logical deduction and reasoning of the physical circuit before you with all its inherent foibles, has been a real master-class.

Should anyone ever come up against a TV27 in the future this thread will serve as a superb reference source.

 
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Re: Dynatron TV27 "Fulmar"

Post by colourmaster » Thu Sep 10, 2015 8:01 pm

Hi David
Excellent progress , that test card looks nearly perfect if you can get some more width out of it .
Regards.
Gary.

 
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Re: Dynatron TV27 "Fulmar"

Post by Cathovisor » Thu Sep 10, 2015 9:07 pm

Till Eulenspiegel wrote:In the original circuit the boost HT might not have been as high as it is now, it is 370 volts. It's likely the HT for the anode of the ECL80 should be 250 volts, but no more.

Well, this is from the ECL80 data sheet held at the excellent website run by Frank Philipse.
Attachments
ECL80.PNG

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Thu Sep 10, 2015 9:18 pm

Hi Chris,
Thank you for those kind words. When I get the timebases sorted out this is going to be an outstanding TV set. The frame oscillator has received some attention, I have introduced some elements of the Ekco TS88 frame oscillator circuit and now the timebase locks up perfectly from the improved sync circuits. The interlace is perfect. It's the line timebase which still causing me some concern.
We've determined that the circuits around the 12AT7 in the video output stage are part of an over engineered white spot suppressor.
The timebases are not perfect but the signal sections are an entirely different matter. This is the part of the set where the Dynatron engineers will have been good at. Many radio enthusiasts will be aware of the excellent radio receivers the company made before WW2.
My next stage of the restoration will be to supply the anode of the ECL80 frame TB pentode from the boost HT supply.
Assuming that the plate current of the ECL80 is 10mA, then a series resistor of 10Kohms will be a good starting point.
Let's find out if that is the answer to the frame TB problems.

Till Eulenspiegel.

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Thu Sep 10, 2015 9:23 pm

Thanks for posting up the information of the ECL80. Looks as if I can get away with an anode voltage greater than 250.
The original series resistor from the boost HT supply was 2.2Kohms. I'll play safe and start with a much higher value.

Till Eulenspiegel.

 
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Re: Dynatron TV27 "Fulmar"

Post by Derren » Thu Sep 10, 2015 9:59 pm

Excellent David :) That is not unlike the image I had as far as size is concerned, BUT by the look of it you've got rid of that nasty frame jitter and very annoying visible fly back lines aswell as intermittent frame hold. As I recall you should easily get extra height but as you imply the width may be the real challenge. Are you satisfied that the picture tube is OK, bearing in mind the EHT has probably not been as high as this previously so I suppose you could say it's never been fully tested? It gave a good picture with the original Dynatron lopt and filled the screen but it was never very bright.

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Thu Sep 10, 2015 10:42 pm

Hi Derren,
Unfortunately, supplying the anode of the ECL80 frame TB valve from the boost HT has robbed the line timebase of considerable power and as a consequence of that the width is much reduced. It looks like I'll have find the extra height by other means. Perhaps another type of frame output valve, one with a much higher slope.
Problems with frame jitter and flyback lines are now a thing of the past as far as this set is concerned.

Till Eulenspiegel.
Attachments
000_0344.jpg

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Thu Sep 10, 2015 11:55 pm

Derren wrote: Are you satisfied that the picture tube is OK, bearing in mind the EHT has probably not been as high as this previously so I suppose you could say it's never been fully tested? It gave a good picture with the original Dynatron lopt and filled the screen but it was never very bright.

The Brimar C17BM CRT is excellent. The picture is very bright and the focus is as good as it can be for a tube which has a simple triode gun.
Nevertheless, the line structure is visible when the picture is at full height.
The EHT is in the region of 13KV which is an ideal voltage for this CRT.

Till Eulenspiegel.

 
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Re: Dynatron TV27 "Fulmar"

Post by Derren » Fri Sep 11, 2015 12:50 am

That's excellent! It certainly looks brighter in your images, I always had to have the room well darkened for this set. Quite like to see the line structure myself so that's no problem either.

 
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Re: Dynatron TV27 "Fulmar"

Post by Derren » Fri Sep 11, 2015 5:32 am

I realise now your point about the lines was that the focus was pretty much OK :) Just a thought about the Ekco lopt, will it manage to fill this 17 inch screen bearing in mind it was originally in a set with a smaller CRT?

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Fri Sep 11, 2015 10:03 am

Hi Derren, The Ekco TC178 line output transformer should be OK because the 15" CRM152 CRT has a 67 degree deflection angle, described in those times as a wide angle tube. The same transformer was employed in the Ekco model T217 which was the companies first 17" set. The CRT was the Mazda CRM171.
On standby there is always that ex Pilot TV84 line output transformer. However, that transformer is driven by the mighty 6CD6G line output valve, also, a curious composite metal disc which was fitted on the top of the transformer has disintegrated. The Pilot TV84 line output stage is very similar to the Dynatron circuit.
In the meantime what I will do to the Pilot transformer is bleed a small current through the overwind in order to warm it up in order to drive out any moisture in the windings.
I have an interesting transformer which was donated to me by French TV enthusiast Wilfrid (wiwior). This transformer has been tried out in all types of TVs including 405, 625 and even 819 line receivers. I have one of these transformers installed in a Pye CTL58.

Read about the line output transformer substitution here: http://www.vintage-radio.net/forum/show ... =Pye+CTL58

Till Eulenspiegel.

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Fri Sep 11, 2015 12:38 pm

You want picture width, how about this? I applied that old trick of connecting a high voltage capacitor between the cathode of the boost diode to chassis. The value picked out because it was simply to hand is 210pF. If a smaller value is chosen that'll be the width problem sorted. Very little reduction of EHT so the picture is still very bright. We're getting there!.

Till Eulenspiegel.
Attachments
000_0345.jpg

 
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Re: Dynatron TV27 "Fulmar"

Post by crustytv » Fri Sep 11, 2015 1:21 pm

Till Eulenspiegel wrote:You want picture width, how about this? I applied that old trick of connecting a high voltage capacitor between the cathode of the boost diode to chassis.
Well that's the cool thing about this thread, lots of useful info, I never knew about that trick.

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Fri Sep 11, 2015 4:02 pm

Hi Chris,
It's an old trick, in fact we used to use it way back in the sixties and it is still valid today even in colour TV line timebases.
The circuits often look look simple enough but the line timebase does involve a lot of brain ache maths.
Well worth discussion in another topic.

The attachment shows the capacitor C131 in the BRC 950 chassis.

Till Eulenspiegel.
Attachments
000_0346.jpg
000_0346.jpg (114.02 KiB) Viewed 1822 times

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Fri Sep 11, 2015 5:19 pm

That's the width sorted. I've used two capacitors in series, 180 and 210pF.
There is still the frame timebase to sort out. I'm not keen on supplying the anode of the ECL80 from the boost HT. The control grid of the frame output valve is receiving 30 volts P - P of sawtooth drive. More than that and the valve will be over driven thus causing non linearity.

Till Eulenspiegel.
Attachments
000_0348.jpg

 
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Re: Dynatron TV27 "Fulmar"

Post by Katie Bush » Fri Sep 11, 2015 8:21 pm

As others have already said, this is an impressive thread and includes a lot of clever stuff - all of which is way beyond my feeble mind!

Now, I'm going back into the corner with a U2 battery, a couple of small torch bulbs and a few bits of wire!... :elc:

Marion

 
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Re: Dynatron TV27 "Fulmar"

Post by Till Eulenspiegel » Fri Sep 11, 2015 10:28 pm

Substituting the ECL80 frame output valve with an ECL83 improves the picture height and linearity somewhat but there is still room for improvement.
The ECL83, PCL83 and UCL83 group of valves was most likely developed in the UK by Mullard. I've never seen one marked as "foreign made". Possibly never used on the Continent in radios and TVs. The MO valve company made their version of the PCL83, the LN309. Also the HN309 which has a higher mu triode section.
The ECL83's main advantage over the ECL80, output power apart which is 5.5W against 1.2W is that the triode and pentode cathodes are brought out to separate pins.

Till Eulenspiegel.
Attachments
000_0350.jpg

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