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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 12th Dec 2022, 7:23 pm   #1
Radio_Doctor
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Default HMV 800 Fuse

I am fortunate to have recently acquired this. Been well restored sympathetically.

It worked perfectly for a few weeks but didn’t switch on yesterday. I think I might have left it on the last time I used it but can’t be certain.

Initial investigation shows the F2 heat coil fuse is OC. I’ve never seen one of these before.

Can I ask please:
1) Any idea where to acquire a new equivalent?
2) How much exploration do I need to do before plugging it in again?

As ever any advice appreciated, Kneale
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Old 13th Dec 2022, 5:10 am   #2
Catkins
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Default Re: HMV 800 Fuse

These heat coils are used on pre-war HMV/Marconi televisions. I have never seen them on a pre-war HMV/Marconi radio. Its presence on a radiogram here may be due to higher wattage or the fact it is a high end "luxury" product like their televisions. As such you may get more responses if the post is moved to the television subsection.

To answer your questions ...

I do not know of any suppliers of these heat coils. In the common case where the heat coil is missing, or open-circuit I have replaced it with a modern glass fuse of the equivalent rating.

As to why it is has failed, that is a fairly unknowable question. In my experience these heat coils are fragile and have often failed due to old age before I got the set. In fact I've never had one fail on me, because I've never had one working!

So it could have failed simply due to old age. But, you shouldn't rely on that, and you should assume something may have caused it to fail.

In this case I would first check the resistance between the HT line and earth, normally it should be at least 15 Kohms, and anything less indicates a potential short has developed.

Going on from there largely depends on whether the smoothing/reservoir electrolytics have been replaced. If they have not, they're the first suspect. If they have been replaced, the next culprits will be decoupling capacitors in the HT line, and whether they've been replaced.

If the above has been replaced, and the resistance checks look OK, I would replace with a modern replacement and see what happens. It is likely it will just work, and it is no point speculating further without knowing the above.
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Old 14th Dec 2022, 12:03 pm   #3
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Default Re: HMV 800 Fuse

I'm not entirely sure, but didn't the Post Office use heat coils at one point in time?
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Old 14th Dec 2022, 1:38 pm   #4
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Default Re: HMV 800 Fuse

They did indeed use them to protect some telephone lines at the exchange.

Let's not drag this thread off topic by discussing this though.
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