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Old 11th Sep 2020, 12:07 am   #1
matspar
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Default 1974 Dynatron CTV21 missing A1 supply

Good evening all,

I have a quick question which I'm hoping some kind person may be able to advise me on.
I'm currently working on this 1974 Dynatron CTV21 fitted with the Pye 671 chassis.

The tripler had failed on this and had also destroyed the line output transistor and C549 (not shown) These have now been replaced but I've been unable to find the correct tripler anywhere, so I've fitted a nos Grundig one mainly as it was to hand.
This has produced 20kv of EHT but I have no A1 voltage, so no screen illumination as yet. The replacement tripler doesn't have the same provision for the A1 supply (shown as red dot on the circuit diagram)

The circuit states this is an 11v rail? so I have supplied this from an external source which hasn't made any difference. There is 60v across the A1 smoothing capacitor C563 (shown as blue dot) but this should of course be far higher.
Can anyone confirm this is indeed an 11v rail or if this should be supplied with the full A1 potential? (around 325v)
I am reluctant to supply a higher voltage at present in case any damage is caused.
Third picture shows the original tripler (type KTS 106) The pair of black leads with red connector are the +/- A1

Any thoughts gratefully received!
Regards
Matt
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Old 11th Sep 2020, 4:05 am   #2
its ur aerial
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Default Re: 1974 Dynatron CTV21 missing A1 supply

This problem sounds familiar, but its all a long time ago.
Not all triplers were compatible, some I recall had a internal extra Diode for the A1 volts, might be worth pulling that red plug and measuring what voltage on the two black wires.
It might be best to check this voltage with a old Analog meter if you have one, back in the day Digi Meters didn't like A1 Volts, not sure about new ones.
Also worth checking the black leads are the right way round, and the A1 supply is not going to deck
I also vaguely remember the Triplers with the A1 Diode having black and white leads ?
But it must be thirty years since I last changed a Tripler...common failure in hot weather.
PS. 70`s Firenza...most impressed.
Ken G6HZG
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Old 11th Sep 2020, 10:17 am   #3
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Default Re: 1974 Dynatron CTV21 missing A1 supply

Thanks Ken, I might dig out the old Avo when I get a moment. The red plug and socket is SK630 on the circuit. One side to deck and the other one looks to be the A1 supply. I have a new Granada mk3 tripler to experiment with which looks like it has the extra diode connection. The bit that confuses me is the 11v side of things. There is a zener and two low voltage caps (D575, C573 C575 straight off this rail. Have to admit it's been a while since I've been near a 70s colour set. I'm a valve man as a general rule!
Would I be right in thinking the A1 supply is put onto this rail? Probably a daft question. I don't want to risk wrecking a new tripler and potentially the transistor, lopt etc!
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Old 11th Sep 2020, 10:58 am   #4
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Default Re: 1974 Dynatron CTV21 missing A1 supply

Hi
Don't worry - as long as the connections are right then you won't wreck anything.
The tripler you need is a six-wire type and the internal diode is necessary for the A1s to sit on.
While you're in there don't forget to change the nasty green line tuning capacitor. That can change value with consequences for the line transistor and, indeed, the tripler.
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Old 11th Sep 2020, 4:09 pm   #5
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Default Re: 1974 Dynatron CTV21 missing A1 supply

If all else fails Matt I have a 25KV 'mini tripler made by HIGH VOLTAGE MODULES LTD.
It is marked D166. It has five connections two of which are bare wire loops. Your very welcome to it if you want to give it a go. FOC of course. Regards, John.
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Old 11th Sep 2020, 5:26 pm   #6
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Default Re: 1974 Dynatron CTV21 missing A1 supply

Oh yeah.. forgot about that Green Cap, most important. Worth taking up the tripler offer from Heatercathodeshort, I think with the right tripler you will be sorted.
Ken, G6HZG VMARS.
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Old 11th Sep 2020, 8:57 pm   #7
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Default Re: 1974 Dynatron CTV21 missing A1 supply

Hi.

C563 was quite troublesome on this series of chassis. I've taken a quote from Mike Phelan's servicing article, TELEVISION magazine, September 1979.


"The line timebase is fairly conventional, using a BU108
output transistor. A feature to note is the method of deriving
the boost voltage for the tube first anodes. The e.h.t. tripler
contains the now usual clipper diode to remove the rings on
the input pulse and improve the e.h.t. regulation. If the
overwinding is not connected to anything else d.c.-wise, it
assumes a potential of about 1 kV above chassis. The
"bottom" end is decoupled by C563 (0.1μF), and supplies
the first anodes. C563 in fact is the bete noire of this chassis.
When it goes short-circuit it gives the symptoms of a faulty
tripler - disconnect the tripler, and the line timebase starts
up. Later sets use an 0.22iuF, 1.25kV working capacitor. If
the set is left on in this condition, the demise of the tripler,
sometimes followed by the BU108 and the line output
transformer, can result before the h.t. fuse blows. Where the
h.t. fuse F971 has blown, C563 should be the first check
therefore. C563 should also be checked whenever the tripler
fails."

The full servicing articles on the series of Pye solid state chassis was from Sept to Nov 1979 and can be found on World (formerly American) Radio History website.

Hope this is useful.

Regards,
Symon
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Old 12th Sep 2020, 12:30 pm   #8
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Default Re: 1974 Dynatron CTV21 missing A1 supply

Many thanks Gents, much appreciated! C563 is now long gone and has been replaced with a shiny new one (original was blown to bits!) John I may well take you up on your kind offer if I don't have a suitable one here. I will let you know how I get on!
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Old 12th Sep 2020, 1:36 pm   #9
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Default Re: 1974 Dynatron CTV21 missing A1 supply

I have a dynatron wth the pye 731-733 chassis and am wondering if a tripler for the redifusion mk4 would be a suitable replacement as its got its own focus pot perhaps John-HKS-would know its suitable regards David
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Old 21st Sep 2020, 2:48 pm   #10
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Default Re: 1974 Dynatron CTV21 missing A1 supply

Great success with a replacement tripler (Granada)
24kv of EHT and even some signals.
Years of damp storage has taken its toll however and there's a long way to go yet! Looks promising though!
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Old 30th Sep 2020, 3:35 pm   #11
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Default Re: 1974 Dynatron CTV21 missing A1 supply

I think its worth trying another focus unit or a check of the degausing thermistor ,have you checked the tubes emission
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Old 1st Oct 2020, 5:34 pm   #12
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Default Re: 1974 Dynatron CTV21 missing A1 supply

Well done Matt. A tip top job.

I think a quick twiddle on the static-convergence would go a long way to giving you a half-decent monochrome picture.

Kind regards.

From Mike.
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Old 2nd Oct 2020, 8:28 am   #13
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Default Re: 1974 Dynatron CTV21 missing A1 supply

The purity looks a bit dodgy too. Easy fixes. J.
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Old 13th Oct 2020, 10:54 pm   #14
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Default Re: 1974 Dynatron CTV21 missing A1 supply

She's all done!
Thanks to everyone for your assistance. A Granada 11TFV tripler is now in place producing 24kv. All set up to the manual. Plenty of dried up caps throughout along with endless dry joints and broken tracks mainly on the chroma board! 2 convergence pots replaced too due to a slight burn up.

So far so good!! I'm living the 1970s dream
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Old 14th Oct 2020, 10:21 am   #15
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Default Re: 1974 Dynatron CTV21 missing A1 supply

Nice job Matt. These were always a bit of a handful even when new.
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