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Old 27th Oct 2008, 11:18 am   #1
'LIVEWIRE?'
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Default Fitting Thermal Overload Trips to Vintage Radios

I KNOW there is a thread on here somewhere dealing with this topic, but I cannot find it. Basically what type, and temperature rating resettable trip should be fitted in series with the mains supply to Radios such as Bush VHF41, 61, etc., and other similar equipment. I was thinking of fitting a bimetallic self-resetting type rated at (say)60 deg. C, mounted above, and as close to, the mains transformer as practical. Any advice/suggestions welcome
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Old 27th Oct 2008, 11:43 am   #2
Nickthedentist
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Default Re: Fitting Thermal Overload Trips to Vintage Radios

Your mind's not playing tricks, Panrock and I were contributors. I have also mentioned using them in my Hacker Mayflower which had obviously caught fire at some point in its life. Sorry, I've not managed to track down the thread(s) yet either.

I use the little black, non-resettable, wire-ended ones made by "Cliff", in the lowest temperature rating I can buy, and bond them to the transformer with Superglue or Araldite.

Nick.
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Old 27th Oct 2008, 1:28 pm   #3
julie_m
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Default Re: Fitting Thermal Overload Trips to Vintage Radios

Don't forget to douse a non-resettable thermal fuse with plenty of freezer spray while soldering it in! Otherwise, you will kill it!

Maplin don't sell the type Nick mentioned; only metal bodied, wire-ended ones. See here.
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Old 27th Oct 2008, 8:02 pm   #4
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Default Re: Fitting Thermal Overload Trips to Vintage Radios

Thanks, Nick and AJS, for the advice, which I will bear in mind. Maybe CPC stock the 'Cliff' trips-must check their website, although, as stated in my post#1 above I was thinking of using self-resetting overload trips, if possible. (I can see the pros & cons for both types)
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Old 27th Oct 2008, 9:28 pm   #5
Leon Crampin
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Default Re: Fitting Thermal Overload Trips to Vintage Radios

I have to say that in many years of dealing with Bush radios, especially the VHFxx series, I've never ever seen a mains transformer failure. Some of them have obviously run pretty hot in the past due to faulty coupling capacitors and smoothing elecrolytics - but they always survive.

Why waste your time? On a properly restored set, I can't see any reason why a mains transformer should ever fail, except perhaps in the event of the two anodes shorting together in a full-wave valve rectifier. I've never seen this happen.

I just fit a 1A HRC BS 1362 fuse in the mains plug. (A VHF64 needs a 3A fuse though).

Leon.

Last edited by Leon Crampin; 27th Oct 2008 at 9:29 pm. Reason: Remembered why my last 1A fuse blew.
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Old 27th Oct 2008, 11:15 pm   #6
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Default Re: Fitting Thermal Overload Trips to Vintage Radios

I would tend to agree with Leon. I have encountered quite a few sets now(must be a few hundred in total over the years) and have had very few mains transformer failiures. I suspect they were over rated slightly.
The only one that actually happened when "I was there" was a KB CR20 when the 6X5 rectifier went direct short heater to cathode. Result, smoke and a most distinctive smell!
(That set has only one heater circuit.)
They might get a bit warm but don't forget most are bolted to a large metal chassis!
If it means you sleep soundly, fit a thermal fuse. It won't do any harm.
Sets here usually have a 2 or 3 amp fuse fited in the mains plug.

Mike, you could always fit a "torpedo" in-line fuse holder with your desired value of cartridge fuse(0.5 amp antisurge??)
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Old 28th Oct 2008, 10:55 am   #7
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Default Re: Fitting Thermal Overload Trips to Vintage Radios

Leon & Tim,
I must admit I hadn't even thought about fitting Overload trips to vintage radios until I saw an earlier thread about it on this forum. Like you, Tim, I have only ever had one failure, which also happened when I was there-this on an HMV11xx. Perhaps fitting an in-line fuse and/or a 1A plug fuse would be simpler!
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