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Old 25th Jul 2020, 9:45 pm   #1
chompy1
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Default Testing Valve TV's and Radios for Insulation leakage

Hi All,

I haven't been on here for quite some time, so I thought it was time to make a return .

Can valve TV's and valve radios be PAT tested?

Thanks, Paul
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Old 26th Jul 2020, 2:25 am   #2
G8UWM-MildMartin
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Default Re: Testing Valve TV's and Radios for Insulation leakage

Yes, but...
Class I (earthed) radios can generally be tested successfully by a non-specialist test person.
A few very late models, particularly German ones, were marked as double insulated and again can be tested by a non-specialist.
The remainder are Class 0 and a can of worms that has been discussed a few times.
Most test people are unfamiliar with this type of equipment and will summarily fail it on inspection. Others may be persuaded that it is to remain in service and test it for insulation resistance or for touch current.

A question for Lucien Nunes?
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Old 26th Jul 2020, 8:23 pm   #3
MotorBikeLes
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Default Re: Testing Valve TV's and Radios for Insulation leakage

This is an interesting question. About 30 years ago, I sold a Grundig CTV to a chap for his mother who was in a local care home. A week later he came back to me saying they had PAT tested it and it failed. I asked him to bring it back to me and I would test it. I knew what the (UK) test requirements were at that time, and sure enough it was just outside. Everything in the TV was correct, so I contacted Grundig Technical who confirmed it would meet the German standards, and therefore, being part of the EU, must be acceptable over here. He gave me details of the relevant German spec against which I tested it, and issued a signed certificate to that effect.
The set was duly installed and used by the old lady.
Les.
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Old 26th Jul 2020, 9:50 pm   #4
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Default Re: Testing Valve TV's and Radios for Insulation leakage

We had exactly the same issue with a Grundig CUC220 or similar in exactly the same situation, as I recall the problem was the value of the resistor across the isolation barrier (4M7) ie. across the chopper transformer primary to secondary in our case, the Firebrigade whom at the time was responsible for said pat test would not listen to reason, we ended up swapping the set out for a Fergy TX100 with the same resistor across the isolation barrier valued at 10M.
I never did get a valid reason why the Grundig should have failed anyway ? as it was well above the minimum resistance anyway, I guess they just "didn't like" the readings!!!
We got accused of sending out substandard equipment, to which I replied "would you be prepared to stand up in court to that assertion?" they never did though.
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Last edited by Red to black; 26th Jul 2020 at 10:04 pm.
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Old 26th Jul 2020, 10:16 pm   #5
chompy1
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Default Re: Testing Valve TV's and Radios for Insulation leakage

Thanks for your replies guys ........... an interesting read .

Do the valves need to be warm/hot for a PAT test to be carried out successfully?

Can sets which are not earthed be PAT tested?
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Old 26th Jul 2020, 11:34 pm   #6
Lucien Nunes
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Default Re: Testing Valve TV's and Radios for Insulation leakage

PAT, or as we should call it 'ISITEE' - In-Service Inspection and Testing of Electrical Equipment - is as much (or more) about inspection as testing. Many common defects are plainly visible as they are the result of use and abuse, which typically wears out the external bits more than the internal. Plugging an appliance into a test instrument and seeing some numbers come up is just a final stage, to catch the relatively small percentage of faults that are not apparent to the naked eye. With this in mind, we could perhaps re-phrase the original question as:

'Can we inspect a valve TV or radio and make an informed decision about whether it is safe to use?'

With a vintage appliance not built to current or recent standards, that consideration is going to be as much about the design as the present condition, and this is where the can of worms is opened as G8UWM describes. But I sense from the OP that the question pertains more to the act of plugging the appliance into a test instrument and seeing the numbers, rather than conducting a risk assessment within a safe system of work (e.g. for compliance with EAW '89)

In a nutshell, yes. Any electrical appliance can be tested with most test instruments, noting that not all instruments can carry out all the same tests. In order:

Earth continuity for Class I equipment: If there's an earth wire, you can certainly test its continuity. Insight might be needed as to where to expect it to be connected and where it actually needs to be connected.

Insulation resistance: For Class I you might want to go easy on the old transformer insulation and test at 250V, but in truth it should hold up 500V although the pass threshold might need to be relaxed a little. If there's a Rifa about to go pop, let it go pop. For Class II, it had better pass or it is potentially unsafe. Class 0? Erm, that should have failed the visual, so how can it be here on the tester now? But yes, pragmatically, press the button and if it's over 7 megs, it's OK as far as Class 0 goes.

Differential leakage, touch leakage: Again, it should pass and if it does not, it's potentially unsafe. The COP suggests only doing either IR or leakage, I do both, and at normal voltage not a substitute (reduced voltage) leakage test. Of course, some product knowledge is useful for deciding where to test for touch leakage, especially on marginal stuff like AC/DC record players.

In summary, some or all electrical tests can often be applied and most vintage equipment should pass; if it does not pass, it may be significantly dangerous. But, and it is a big but, the electrical test is only one of a number of boxes to tick, of which the safety of the design is probably the most crucial for pre-1970s equipment. Due to lack of specific knowledge and experience, many test operatives will not be able to make an informed judgement on this; even experts will tend to disagree among themselves.

Context is important here; can you give some background to the original question?
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Last edited by Lucien Nunes; 26th Jul 2020 at 11:40 pm.
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Old 30th Jul 2020, 9:21 am   #7
chompy1
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Default Re: Testing Valve TV's and Radios for Insulation leakage

Thanks for your reply guys, much appreciated. A friend of mine is interested in purchasing one of my valve radios and I want to make sure the set is safe for long term use before I sell it.
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Old 30th Jul 2020, 5:26 pm   #8
Welsh Anorak
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Default Re: Testing Valve TV's and Radios for Insulation leakage

Slightly OT, but this TV with a current PAT came in for repair from a hotel bedroom. Maybe the numbers were good, but...
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Old 30th Jul 2020, 5:35 pm   #9
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Default Re: Testing Valve TV's and Radios for Insulation leakage

Classic threaded through something for neatness. oops.
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Old 30th Jul 2020, 5:41 pm   #10
Dennis M
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Default Re: Testing Valve TV's and Radios for Insulation leakage

Quote:
Originally Posted by Welsh Anorak View Post
Slightly OT, but this TV with a current PAT came in for repair from a hotel bedroom. Maybe the numbers were good, but...
If you think that is bad I found twisted and sellotaped single insulated wires on a bedside lamp in a holiday let.
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Old 30th Jul 2020, 5:47 pm   #11
OldTechFan96
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Default Re: Testing Valve TV's and Radios for Insulation leakage

Also slightly OT:

I have a photograph somewhere of an ivory MK plug from the 1950's with a PAT sticker on it.

It's nice to see old plugs still in service. Although I thought unsleeved pins were an automatic fail?
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Old 31st Jul 2020, 9:32 pm   #12
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Default Re: Testing Valve TV's and Radios for Insulation leakage

Quote:
Originally Posted by Dennis M View Post
Quote:
Originally Posted by Welsh Anorak View Post
Slightly OT, but this TV with a current PAT came in for repair from a hotel bedroom. Maybe the numbers were good, but...
If you think that is bad I found twisted and sellotaped single insulated wires on a bedside lamp in a holiday let.
I've seen similar, but with insulation tape and in mini trunking, couldn't remove the TV as it was an owners van, wasn't happy when I was back in the van at a later date and the failed stickers had been removed . Got fixed properly in the end.

Also some people should not be allowed to wire mains plugs!
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