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Old 7th Oct 2015, 11:09 pm   #1
AdamDynamic
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Default Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Hi,

I recently bought a job lot of Rediffusion Mk1 TVs from a retired TV repair man which I'm in the process of trying to revive and see how many I can get to work.

The guy I bought them off suggested that as they've been in storage for a while that I should warm up the capacitors by passing ~10v through the sets first (using a variable transformer) before trying to put 240v though them.

Does this sound like a sensible approach? I'm having some difficulty getting my hands on a variable transformer to do the job (they are pretty expensive for something I'm likely never to use again), are there any 10v (or 12v etc?) power supplies that would do a similar job that anyone could recommend?

I've been scouring the internet looking for assistance getting these working, any help would be much appreciated!

Thanks,

Adam
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Old 8th Oct 2015, 12:45 am   #2
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

A 100W traditional light bulb connected in the mains feed can be substituted for the variable transformer.
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Old 8th Oct 2015, 12:46 am   #3
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Hi Adam, no point running these sets up on a variac. Snip out the mains filter cap located on the back of the on/off switch and apply mains. Make sure the sets are dry. Keep them in in a dry warm room for a week or so to be certain.

I worked on these sets for years when I worked for Rediffusion w/shop. I am restoring a CU2213 now. Malc.
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Old 8th Oct 2015, 7:44 am   #4
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Thanks for the responses everyone.

Quote:
Originally Posted by MALC SCOTT View Post
Hi Adam, no point running these sets up on a variac.
Ah ok - the guy I bought them off mentioned a couple of times that it was something I should do (and he had about 200 of these sets in storage when I bought my ones). Would trying it have any effect (or would I just be wasting my time?) Not using a variac would save me a lot of hassle but I just want to be sure.

Quote:
Originally Posted by MALC SCOTT View Post
Snip out the mains filter cap located on the back of the on/off switch and apply mains.
I've never opened up a TV like this before but I'm aware that there are some extremely high voltages in them. How safe is this step to perform for an 'amatuer'? Are there any photos online that would show me what I'm looking for?

Quote:
Originally Posted by MALC SCOTT View Post
Make sure the sets are dry. Keep them in in a dry warm room for a week or so to be certain.
They've been sat in my living room for a couple of weeks now (all 11 of them) - part of my urgency to get them sorted is my other half asking me what I'm going to do with them.

Thanks again for the assistance.

Adam
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Old 8th Oct 2015, 3:23 pm   #5
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

I have just restored a 1974 Mk1 which had never been used since 1985. The filter capacitor was cut out and mains was applied. All that was needed was a PL509 valve replaced as it was cracked, to get the set running. It needed one or two minor repairs to get it up to spec. Remove the back cover and you will find the filter cap mounted on the back of the on/off switch. Cut off one leg, it may be cut off already. Malc.
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Old 8th Oct 2015, 10:46 pm   #6
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Thanks for the info - it doesn't sound too complicated? I'll take the back off one this weekend and see if the filter cap looks obvious (I may be back here to post a photo and check

Out of interest, what's the purpose of removing the filter cap? My guess would be it was included in the design of the TV for a reason?
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Old 9th Oct 2015, 10:26 am   #7
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

To prevent any rubbish going back into the mains.
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Old 9th Oct 2015, 10:33 am   #8
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

...and causing interference on radios, digital stuff to crash etc.
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Old 9th Oct 2015, 12:55 pm   #9
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

So removing the capacitor causes digital devices to crash/causes rubbish to go back I to the mains, or leaving it where it is causes the problem?

Apologies for the stupid questions, just keen to understand what I'm doing before I start cutting pieces off the TVs
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Old 9th Oct 2015, 1:04 pm   #10
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

It's removing it which causes the problem with interference.

The reason for removing these devices before applying mains power is that they have a habit of exploding when awoken from years of slumber.

You can replace it with a Class X capacitor later if you wish.
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Old 9th Oct 2015, 2:01 pm   #11
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

There is so much poor quality electronic kit being sold these days that the filter capacitor less of a benefit.
I would just say that it is optional these days.
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Old 9th Oct 2015, 9:01 pm   #12
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Quote:
Originally Posted by Station X View Post
The reason for removing these devices before applying mains power is that they have a habit of exploding when awoken from years of slumber.
Based on the advice of the guy who sold me the TVs, it's the exploding bit was what the variac 'warming up' step was designed to avoid

Are the capacitors safe to just cut off/dispose of? The TVs haven't been used for a whlie (though I don't know exactly how long) and I'd be a bit concerned about accidentally shorting the legs with my wire cutters? Any safety tips would be appreciated.

In terms of replacing the cap, am I correct in thinking that these are what I'm after? Is 2.2uF enough/too much?

Thanks again for all your help with this guys, really appreciate it.

Adam
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Old 9th Oct 2015, 9:13 pm   #13
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

I can't say I've ever heard of "warming up" capacitors before. I assume the person who suggested this meant reforming electrolytic capacitors which is a common procedure. The mains filter capacitor isn't of the electrolytic type and attempting to reform it may cause it to explode.

Snip out the mains filter capacitor leaving wire ends which are too short to touch each other or bent so they don't touch each other. This will make it easier to grasp the wires with thin nosed pliers when you unsolder them later and fit a new capacitor should you wish to do so.

The replacement capacitor must be a CLASS X TYPE.
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Old 9th Oct 2015, 9:21 pm   #14
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Quote:
Originally Posted by AdamDynamic View Post
Are the capacitors safe to just cut off/dispose of? The TVs haven't been used for a whlie (though I don't know exactly how long) and I'd be a bit concerned about accidentally shorting the legs with my wire cutters? Any safety tips would be appreciated.
Yes, they can go in normal domestic waste, or ideally, the WEE recycling bin at the supermarket or wherever.

The caps will be perfectly safe to snip out a few minutes after disconnecting from the mains at most, so if they've not been powered-up for years, you'll be fine.

N.
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Old 9th Oct 2015, 10:44 pm   #15
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Hi Adam

Take a look here
http://www.radios-tv.co.uk/?page_id=16489
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Old 10th Oct 2015, 12:38 am   #16
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Quote:
Originally Posted by Station X View Post
I assume the person who suggested this meant reforming electrolytic capacitors which is a common procedure. The mains filter capacitor isn't of the electrolytic type and attempting to reform it may cause it to explode.
Reforming the capacitors sounds like what the guy I bought them from was referring to. I'm happy to skip the reforming step and avoid any explosions.

Quote:
Originally Posted by Station X View Post
Snip out the mains filter capacitor leaving wire ends which are too short to touch each other or bent so they don't touch each other. This will make it easier to grasp the wires with thin nosed pliers when you unsolder them later and fit a new capacitor should you wish to do so.
Having looked at the link that Mike C helpfully posted, there seems to be a lot going on inside the TV itself. Any idea which one of the capacitors in this picture I should be cutting?

Quote:
Originally Posted by Nickthedentist View Post
The caps will be perfectly safe to snip out a few minutes after disconnecting from the mains at most, so if they've not been powered-up for years, you'll be fine.
Something to think about if I ever plug in/test/unplug the TV, thanks for this!

Quote:
Originally Posted by Mikey66 View Post
This is very helpful, thanks!
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Old 10th Oct 2015, 1:22 am   #17
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Don't get too exercised by the expression "explosion". As a rule it happens when the back is on the set, and results in a blown fuse. You might get a bang as the set dies, and a puff of smoke. The capacitor in question may have one end blown off, making it obvious.
There are exceptions of course, but the usual fault report is just "I heard a bang and it went off"
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Old 10th Oct 2015, 8:42 am   #18
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Back in the 1970s a mate of mine was fixing a dual standard set and the filter capacitor was in two bits.
The fault was that it went pop with a puff of smoke and then came back on again.
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Old 10th Oct 2015, 9:27 am   #19
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

Quote:
Having looked at the link that Mike C helpfully posted, there seems to be a lot going on inside the TV itself. Any idea which one of the capacitors in this picture I should be cutting?
If you scroll down the page linked to by Mikey66 you'll see a drawing and picture clearly identifying the filter capacitor.
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Old 10th Oct 2015, 10:52 am   #20
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Default Re: Reviving a Rediffusion Mk1 - variable transformer to 'warm it up'?

..... and if you search on the page for C901, that will take you straight to it.

Watch out for Lockfit transistors on the colour decoder board ..... they may be becoming unreliable by now, but can be substituted by equivalents in TO92 packages.
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