Dynatron TV21 Falcon resto, 1948

[murphyv310]

Hello.
I had a nice visit this afternoon from Mikeymushradio (Mike) this afternoon. He brought some nice goodies and an amazing Dynatron consol type TV21 for me to restore (he might not get it back).
It was from MBL's collection and is a truly beautiful set with a build quality second to none.
I intend to restore this set for Mike to the highest standard, it certainly won't be a weekend job so watch this thread.
The chassis is destined for Mike's Ether so I may land up with this superb cabinet which I will look out for another suitable chassis (I wish)
Anyway watch this space

[murphyv310]

Another picture

[matthewhouse]

That's a cool telly, it's interesting how everything comes out of the cabinet as one chassis. I like it when things are built properly. Please keep us updated!

[FERNSEH]

Hi Trevor,
That's the kind of TV I like, beautifully over engineered beyond the point where it makes sense. My RGD 2347T is constructed in a similar manner.
I'll take some photies of it.

DFWB.

[murphyv310]

Brilliant David, I am looking forward to your pics and of course restoring the Dynatron.
I have to admit the 405 line era does so much more for me than the stuff from the mid 60's onward and those not so well engineered Colour sets, but I suppose every man to their own thing!

[Tazman1966]

Fabulous condition of the cabinet Trevor. Any ideas for the mask?

Originally Posted by murphyv310

I have to admit the 405 line era does so much more for me than the stuff from the mid 60's onward and those not so well engineered Colour sets, but I suppose every man to their own thing!

About 1958/9 onwards is my bag. Must be an age thing I suppose. Anyway, back on topic, what in stages do you think you are going to tackle this set?

[murphyv310]

Hi Tas
Well I am not too sure what Mike has for the "Ether" although he brought along another mask but not from a Dynatron.
Today I am going to have a look at the power supply, it is fully isolated and has mains derived EHT, the fuse holder is broken but I have an exact replacement as is one pin of the mains connector but it looks an easy fix. I intend to have a careful look around then wind the set up slowly on the variac, fortunately there is no 'orrible electrolytic caps just the nice oil filled types that rarely go, so it will be interesting to see what happens.
There is a Visconal EHT smoother that will be disconnected for the initial testing but it will be re-stuffed with a nice modern cap.
I will take some more photos this afternoon and report back here.

[Tazman1966]

Looking forward to it

[Boom]

What size is the tube? I have a rubber mask around here somewhere from a 12" set.

[chipp1968]

That looks nice .I love well constructed things with big valves and big speakers!
My main Tv interest is anything up to about 1961 ,But I like later too especially early colour sets .
Looking forward to seeing this working .I hope the you can find a new mask. The black ones seam to degrade worse than white ones .

[Mikey405]

Wow, what a well-put-together monster that is - I bet it weighs a ton. It looks like a corker of a set - I look forward to seeing it working Trevor.

Kind regards.

From Mike.

[murphyv310]

Well today I made a lot of progress with the set. Firstly I fitted a new fuse holder, and repaired the on/off switch which was o/c, I also repaired the mains input but hard wired a temporary mains lead. I nearly did a John Wakely but just slowly wound the set up on the variac (45 minutes) at 160v mains I heard weak sound (from channel 1) at 200v the sound was excellent and the line stage sprung to life but it was very weak. The line drive from the T41 to the EL38 was 22v positive I at this point replaced the 0.01uf coupling cap to the control grid of the EL38 and the T41 anode load that had risen from 180k to over 400k, re-powering the set up gave me -7v drive, I would have thought it was low but the EL38 in this circuit should be OK. At this point the first Visconol in the doubler (this set doesn't have mains derived EHT which I thought it had after looking at the size of the mains tranny ) was getting warm. I decided to replace all three caps. After switching on again there is no EHT but a reasonable spark from the LOPT so tomorrow I will replace the two EY51's and see what transpires.

[murphyv310]

Hi.
I fitted a couple of new EY51's today and landed up with a nice bright frame collapse, so I know the tube is really good. I then set about the frame stages, there was o/p from the T41 frame osc and a couple of caps got it running nice and sweetly but still no scan. After a few checks I found that the frame side of the scan coils are open circuit.
I have peeled back the tape around the coils but to no avail the fine leads disappear into the coil so I am afraid we need to look out for a set of coils. Its possible anything from the era will work but sadly I don't have anything in my spares box.

[murphyv310]

Hi.
Just one photo with the frame collapse and a temporary mask around the tube. I will need to get some solvent to remove all the old black rubber.
Time for a wanted for some scan coils!

[FERNSEH]

Hi Trevor,
The frame scan coils could be of the high impeadance type. The coils are in a circuit where the coils are series fed though a electrolytic capactor from the anode of the output valve.
No output transformer is used and an anode load resistor is used instead.
The pentode output valve is often triode connected to reduce the Ra.

DFWB.

[murphyv310]

Hi David.
I would judge that they are high impedance by the thickness of the wire.
I do believe though there were a few sets around that fed the frame scan coils that way.
It's a pity though as there is video to the tube, the line locks up and I am sure I would have had a picture except for the scan coil fault.
Anyway its boxed back up in the meantime till I get a set of coils.

[Heatercathodeshort]

The ULTRA W720 series uses a UL41 with a 4k anode load resisitor for frame output. A 40uf capacitor feeds the high impedence scan coils. I think this is a nasty arrangement and I'm surprised Dynatron used this set up. The wire is very thin rather like the primary of a sound output transformer hence it'd failure. Unfortunately these Ultra models are as rare as your TV21 but you never know what turns up! I presume this dates from around 1950 by the voltage doubler arrangement. You could fit a standard frame output transformer and coils to get it going. I have a few pairs of coils Trevor if you fancy having a go. Dynatron designs were often rather dated but proven. Regards, John.

[murphyv310]

Hello John.
I was thinking about modifying the circuit to a more conventional set up, Mike though has a set of Ambassador coils which work the same way so I will give them a shot first if no good I'll go down the conventional road and get back to you if I need some coils.
Many Thanks

[murphyv310]

Hi
I now have a set of coils and a suitable o/p transformer so the circuit will possibly be modded for low impedance scan coils, though David Boynes is heading this way today and bringing a set of high impedance coils too so I will try both and see what scenario is best so watch this space ofer the week end!

[murphyv310]

Hi.
Well I fitted the low impedance scan coils along with an o/p transformer and I now have a picture, not very good but at least I can see what needs to be done now. The CRT is bright but has an intermittent Heater Cathode short, give the neck a tap and it clears, the RF unit will need to be re-capped but I dont have a diagram although I am making headway without one. Most of the front controls are duff but I should have suitable replacements.
I will post some pictures later.