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Old 29th May 2018, 8:36 pm   #1
FERNSEH
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Default Masteradio T852 gone off with a bang!

Remember the Masteradio T852? It was the subject of a topic I started in 2013.
https://www.vintage-radio.net/forum/...ad.php?t=93927

Well it has developed a fault, gone off with a loud bang. Let's find out what has happened to this interesting set.

DFWB.
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Old 29th May 2018, 8:46 pm   #2
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Default Re: Materadio T852 gone off with a bang!

Aha ! The return of the ugly duckling
Why is it that actually love the look of this set ?

Marc.
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Old 29th May 2018, 9:02 pm   #3
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Default Re: Materadio T852 gone off with a bang!

Hi Marc,
I think the set would look even better if it had been supplied with the optional radio receiver. That blanking plate for the radio aperture is a strange looking thing.
I'm sure the cabinet designer could have come up with something better.
I'm still on the lookout for the correct radio chassis. Uses three valves, 12BE6, 12BA6 and 12AT6.

DFWB.
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Old 30th May 2018, 6:36 am   #4
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Default Re: Materadio T852 gone off with a bang!

With a bit of luck I hope that BANG Has finished it off! John.
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Old 30th May 2018, 7:04 pm   #5
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Default Re: Materadio T852 gone off with a bang!

Hi John,
That ain't necessarily so, the set can be returned to working order, of that I'm sure.
It's a fault in the line timebase. The sound is OK and it can be assumed that the visions circuits are in order, also.

DFWB.
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Old 30th May 2018, 7:06 pm   #6
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Default Re: Materadio T852 gone off with a bang!

Maybe the main smoother has gone up like a rocket and necked the tube in the process. We can only hope
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Old 30th May 2018, 7:15 pm   #7
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Default Re: Materadio T852 gone off with a bang!

If the smoothers gone splat it really will be a Materadio…..(I failed the interview)

Lawrence.
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Old 30th May 2018, 7:33 pm   #8
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Default Re: Materadio T852 gone off with a bang!

"Maybe the main smoother has gone up like a rocket and necked the tube in the process. We can only hope"
"If the smoothers gone splat it really will be a Materadio…..(I failed the interview)"

It's just after 8:30pm. I'm off to the shop. Let's see what can done to fix this much maligned set. It has to be saved, there can't be any other Masteradio T851/2 sets still existence.

DFWB.
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Old 30th May 2018, 8:58 pm   #9
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Default Re: Materadio T852 gone off with a bang!

Look at this! Two waxies in the line output stage have gone bad, one a dead short circuit. There's a burnt out resistor in there as well. Change those parts and the Masteradio will live again.
Those Hi-Viz capacitors should be replaced as well, with TCC 343 restuffed waxies.

DFWB.
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Old 30th May 2018, 9:20 pm   #10
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Default Re: Materadio T852 gone off with a bang!

While you're in there, check the values of those ceramic-tube resistors: the high-value ones have a tendency to go a lot-higher with age (I've had a 470K one achieve its lifetime aspiration to become a 1.5Meg) particularly if they're subjected to heat.
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Old 30th May 2018, 10:11 pm   #11
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Default Re: Materadio T852 gone off with a bang!

Quote:
Originally Posted by FERNSEH View Post
Look at this! Two waxies in the line output stage have gone bad, one a dead short circuit. There's a burnt out resistor in there as well. Change those parts and the Masteradio will live again.

DFWB.
It's good to know it will live again David, I'm sure John will be delighted too
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Old 31st May 2018, 8:12 am   #12
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Default Re: Materadio T852 gone off with a bang!

The problem is, David keeps on burying it and then carrying out an exhumation.

Please salvage the tube for a nice Ekco conversion David then carry out a cremation.

By your description of explosions etc it sounds like it is 50% of the way there.
It does not want to live. J.
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Old 31st May 2018, 8:59 am   #13
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Default Re: Materadio T852 gone off with a bang!

Hi John,
We'll know today if the Masteradio will live on after the disaster that had fallen on it.
The line output stage is typical of the type found in TV sets made in the late forties and early fifties. It can be seen that the energy reclaim diode V15 is effectively in series with the line output valve and provides extra HT voltage for the output valve, about -50volts. Note the Miller "Transitron" line oscillator. This circuit provides an extremely linear sawtooth waveform to the grid of the line output valve.

The circuit of the line output stage is similar to Pye LV20.

DFWB.
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Old 31st May 2018, 4:27 pm   #14
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Default Re: Materadio T852 gone off with a bang!

I'd imagine that all Forum members will breath a sigh of relief at the great news that the Masteradio T851/2 is working again.
The line output valve screen feed resistor was burnt as well as the 100 ohm cathode bias resistor. The offending capacitors have also been replaced.

Just few more jobs to do before the chassis is reinstalled into the cabinet,

DFWB.
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Old 31st May 2018, 4:31 pm   #15
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Default Re: Materadio T852 gone off with a bang!

BANG! I hope this will be the end of this pink gin receiver [if you can call it that!]

Shame it popped the neck. My T161 will have to wait. J.
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Old 31st May 2018, 8:08 pm   #16
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Default Re: Materadio T852 gone off with a bang!

Well done David but do you not think that perhaps I should take custody of said little set and keep it from Johns evil fiery gaze ?

Marc.
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Old 31st May 2018, 8:20 pm   #17
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Default Re: Materadio T852 gone off with a bang!

Quote:
Originally Posted by FERNSEH View Post
The line output valve screen feed resistor was burnt as well as the 100 ohm cathode bias resistor. The offending capacitors have also been replaced.
It must make a pleasant change doing a repair rather a restoration.
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Old 31st May 2018, 9:26 pm   #18
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Default Re: Materadio T852 gone off with a bang!

Station X wrote: "It must make a pleasant change doing a repair rather a restoration."

Hi Graham,
That's right all the messy work done to this set was five years ago.
But how did those waxies escape my attention? All the others have been replaced with hi-viz components. I intend to replace those with restuffed TCC and Dubilier capacitors.
Hi Marc,
The truth is I'm sure John would love to have this set in his collection.

DFWB.
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Old 1st Jun 2018, 5:03 pm   #19
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Default Re: Materadio T852 gone off with a bang!

Collection of what David? J.
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Old 1st Jun 2018, 8:23 pm   #20
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Default Re: Materadio T852 gone off with a bang!

Quote:
Originally Posted by FERNSEH View Post
But how did those waxies escape my attention?
You probably thought you'd already restuffed them?

The better job you do, the less certain you become of which ones have been done and which are still to do. The little blighters can lead you round in circles so you miss a couple which are left lying in wait....

Odd little bloodshot telly.

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