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Old 17th Jul 2017, 1:34 pm   #1
osx86apple
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Default Decca 101 restoration

Hello everyone

Currently in midst of a second television restoration a nice 9" Decca 101 console set. Basically had about 50 years of dust in it and no components looked like they were ever replaced. Most if not all wax capacitors have been replaced with some resistors done on the line output stage, I now get a line whistle however no screen what so ever. Any thoughts? Line output valve glowing (not red hot) and I can get a faint spark off the anode but certainly nothing more than that. This is only my second attempt at restoration with televisions. Mainly been use to radios, so any advise would be muchly appreciated.
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Old 17th Jul 2017, 2:19 pm   #2
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Default Re: Decca 101 restoration

Hi.
Is there any spark from the top cap of the EHT rectifier? Is the rectifier alight? Usually the heaters for the EHT rec are fed from the Line transformer so are a sign that the line stage is working or not.
Have you tried replacing the line output valve and boost rectifier? I'm not familiar with the chassis. I assume it is flyback EHT?
You say the line output valve is not overheating but is it running normal hot?
If the valve is cool it may be low HT. Is there any sound?
Hope this helps.
Kind regards.
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Old 17th Jul 2017, 2:26 pm   #3
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Default Re: Decca 101 restoration

What type of chassis is you 101 fitted with? Is it the single unit Plessey Mark 1, that's the one with the self oscillating line timebase or is it the two unit type with mains EHT.

DFWB.
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Old 17th Jul 2017, 3:14 pm   #4
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Default Re: Decca 101 restoration

The info I found on the web says it is an EY51 and there is an EHT capacitor of 1000pF but no efficiency diode.
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Old 17th Jul 2017, 4:31 pm   #5
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Default Re: Decca 101 restoration

the Decca 101 normally has a Mazda 12" CRM121, I looked at a set for someone a few years back but the lopt was physically missing and the tube was as flat as pancake so went no further.

How did you get on with the EHT output capacitor OSX86apple ?
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Old 17th Jul 2017, 7:00 pm   #6
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Default Re: Decca 101 restoration

Hi Everyone

Thanks for the replies. Its the mk1 plessey chassis single unit, no mains eht. Looking at this from research it should be a nice simple circuit to fix.

All valve heaters are glowing, line output glowing and you do get the line whistle noise, however I would say it does have quite a weak spark from the line output valve, certainly no strong spark, guessing I should try a new rec valve and see?

Line output capacitor restuffed all successfully! I'm just hoping the crt isn't dead
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Old 17th Jul 2017, 9:46 pm   #7
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Default Re: Decca 101 restoration

The HT supply to the line timebase should be >240volts. You can measure this at one end of the screen feed resistor of the EL38. The line timebase operates as a type of Miller transiton oscillator. Forward part of the scan comes from the ramp waveform developed in the primary of the line output transformer and the flyback is a function of the capacitor connected between the screen and suppressor grids of the EL38. The spark present at the anode will be tiny and at the anode of the EY51 only 4 to 5 mm. EHT is between 6 to 7KV.
It has to be an EL38 in this type of chassis. Beam tetrodes like the Mazda 6P28 won't work properly.
The metal HT rectifier is not the usual 14A86 type. It's special one for this set.

DFWB.
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Old 18th Jul 2017, 10:56 pm   #8
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Default Re: Decca 101 restoration

Hi OSX86apple,
That's a rare beastie you have there. Any chance of some photos?

Cheers
Andy
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Old 19th Jul 2017, 12:40 pm   #9
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Default Re: Decca 101 restoration

Hi everyone

Line output must be doing something, I can hear changes with the vert. and horz. pots adjusted. Sounds like a clicking noise coming from inside the crt? I've yet to carry out further checks due to my test meter gone missing.
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Old 19th Jul 2017, 1:24 pm   #10
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Default Re: Decca 101 restoration

Has this set got a EHT reservoir capacitor?
If so it can be disconnected as a test. try removing the anode cap from the tube and see if the time base comes back to life. (hang cap away from harms way) It could be that the CRT has a short or has lost its vacuum. Is there any signs of sparking in the neck? Are the CRT heaters alight normally?
Rich.
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Old 19th Jul 2017, 5:12 pm   #11
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Default Re: Decca 101 restoration

I would second that. J.
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Old 19th Jul 2017, 6:12 pm   #12
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Default Re: Decca 101 restoration

Thanks guys. I did disconnect it and it made no difference, looking at it a little further again the clicking is coming from the IF stage?!

Crt heaters glowing normal and no sparks present in the crt. I hope it isn't dead!
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Old 20th Jul 2017, 6:37 pm   #13
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Default Re: Decca 101 restoration

Definitely the clicking is coming from the IF stage.? I have another EL38 to try tomorrow.

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Old 20th Jul 2017, 8:29 pm   #14
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Default Re: Decca 101 restoration

At this stage you just want to find out if the CRT is good.

Any glow from the EY51? Did you replace it?
HT voltage?
CRT grid and cathode voltage?
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Old 21st Jul 2017, 7:52 pm   #15
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Default Re: Decca 101 restoration

Ey51 is glowing and I have also replaced this recently. There is a weak spark from the anode, HT voltage seems very low to me but my test meter has gone astray so can't measure it
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Old 21st Jul 2017, 8:15 pm   #16
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Default Re: Decca 101 restoration

You need to find a meter, the HT may be shorting somewhere in the IF stage which is the clicking you can hear.
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Old 21st Jul 2017, 9:45 pm   #17
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Default Re: Decca 101 restoration

We have light! With terrible frame collapse but I'll get to the bottom of that this weekend hopefully.
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Old 21st Jul 2017, 9:49 pm   #18
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Default Re: Decca 101 restoration

What did you find that was causing the issue?
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Old 21st Jul 2017, 9:58 pm   #19
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Default Re: Decca 101 restoration

One of the problem is with the variables for brightness and frame hold. They need a good clean and I stupidly hadn't thought to check.
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Old 22nd Jul 2017, 7:27 pm   #20
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Default Re: Decca 101 restoration

The tracks are typically broken on the variables, any idea of good, reliable replacements?
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