Problems with valve radio

I have a Bush radio presented to my Grandfather in 1956. He used it daily, but it hasn't been used for at least 20 years, probably nearer 40, and today, it is silent. The dial is illuminated and all the valves are glowing, but nothing from the speaker, not even crackling when dials (on/off volume, tone, tuning and waveband) are rotated. Tried an external speaker, still silent.
Any thoughts? Can a valve fail but still glow? The extent of my knowledge is don't poke around because of high voltages!
--
Graeme

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On 31/08/2018 16:29, Graeme wrote:

Loss of HV at a guess...rectifier tubes can fail, resistors fail, caps fail etc, etc
There are plenty of Youtube videos with good information on servicing valve appliances.
Best advice really, is that if you are not confident around modest voltages (150-300v) then find someone who is :)
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Yes indeed. One fairly safe thing to do is to carefully remove each valve from its holder. There could be screening cans and spring retainers, then a squirt of contact cleaner in the holes and a wipe over of the pins. Do them one at a time, and wiggle them as they go in. When all done try it. Probably be a waste of time, but you might at least have some life indications from that. As I said before though, if the ht fuse has gone then its probably really a job for a competent engineer. Brian
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On 31/08/2018 17:43, Brian Gaff wrote:

Don't spray with contact cleaner! Some valve bases were made out of poor quality paxolin/tuffnel and the contact cleaner can cause the HT to track across with a possible fire. This was very apparent on some "vintage" Ferguson Radiograms with the valve bases and waveband selection switch. I remeber them well from my apprenticeship days.
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On Fri, 31 Aug 2018 17:43:07 +0100, "Brian Gaff"

If you do try removing the valves, grip them by their bases if they have them, rather than by the glass envelope, as the glue holding the envelope to the base gets brittle with the heat and over time, and you may find yourself holding the envelope with a bundle of broken wires sticking out of the bottom, and the base still firmly in its socket. DAMHIKT.
--

Chris

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In the early 60s I fixed our old wartime Ministry of Supply radio by replacing the diode, which had failed, and there was a lead from a tetrode that had come adrift from somewhere so I soldered it to the HT line. It worked well enough after that.
The diode going o/c would be enough to mean nothing at all from the speaker.
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On 31/08/2018 16:29, Graeme wrote:

Yes. Although the length of time it will glow for if the vacuum inside the envelope has deteriorated is severely limited. Usually it is old HT capacitors that tend to give up the ghost first - sometimes by dripping flaming wax onto the floor so don't leave it unattended!
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Regards,
Martin Brown
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Or exploding electrolytic leaving foul smelling bits of debris everywhere for months. I did this with an uncased tv once, my mother was not pleased. Brian
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On Fri, 31 Aug 2018 17:46:42 +0100, "Brian Gaff"

For a really spectacular effect have the Selenium rectifier in some old sets fail. The smell stays until you sell the house which you usually have to do after about 6 months when you realise the aroma is never going to fade.
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On 31/08/18 22:32, Peter Parry wrote:

I dunno. I think I finally discovered the last piece of cat urine soaked hpouse te day before yereday - the MDF riser for the bottom stair tread.
Now replaced with a car body filler frontage in case.
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Most likely power supply related. Usually there is a huge hum, but if the capacitors shorted out then maybe the ht fuse has gone. For something like this, if you really do want it to work, be prepared to let a specialist have it for at least a couple of months and a big bill. The trick with old gear is to use them at least once every few months. I have done this with a Rogers amp and its still working from 1965. Brian
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wrote:

At that age most of the capacitors, both paper and electrolytic will have dried out and failed. Without replacing these any other fault finding is futile. "Recapping" (replacing all the wax paper and electrolytic capacitors) is fairly straightforward if you have soldering skills and modern replacement components are cheap and physically a lot smaller than the old ones so there is usually space to fit them in. There is no guarantee that this will cure the problem but it usually does.
If you don't have moderate skill with a soldering iron and working on old radios you may have to go hunting an aged wireless repairer, there are still a few about.
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On Fri, 31 Aug 2018 16:29:57 +0100, Graeme wrote:

Yes. What do you mean by "glow"? A redish glow from deep inside the metal work inside the valve or a dim purple/blueish glow around the metal work?
The redish glow is the heater, required to release electrons from the cathode. The blueish glow has various sources and isn't generaly a problem but does indicate that the HT is present. Not having ablueish glow doesn't mean there is no HT.
As others have said, inspect the thing looking for obviously burnt/failed parts. Reseat the valves, no contact cleaner. The getta on the inside of the glass envelope (probably at the top) of each valve should be silvery and can be quite a dark silvery. If it's white air has got in and the valve is useless.
--
Cheers
Dave.
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Yes, but it isnt that common a failure mode.

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On Friday, 31 August 2018 16:30:08 UTC+1, Graeme wrote:

I'd start by checking the HT supply. But as others have said most of: HT is 100s of volts. You need basic comptence to play with it There will be capacitor failures that need fixing to avoid further damage Many old valve sets were transformerless live chassis sets, again you need to understand the issues with that.
Valves are usually replaceable or repairable. More likely to be faulty elsewhere.
NT
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snipped-for-privacy@gmail.com scribeth thus

If you feel confident looking at a few hundreds volts than suggest with a decent multimeter if you have one look at all the numbers on the valves and Google them until you find one entitled "rectifier" then have a look at the base diagram and ignore the heater pins but look for the anode should be two off (maybe one in some designs) and the cathode that should have around 200 or more volts DC on it. Negative lead or "- "lead to the chassis metalwork!
If it doesn't switch to AC volts then check the anodes and see if there around the same or more on them. Then report back here!
WARNING only attempt these measurements if you are sure you can do them and feel confident to do so and best bet keep ONE hand in your pocket that prevents an across the chest electric shock!
BUT ONLY IF YOU FEEL COMPETENT TO DO SO!!!
--
Tony Sayer


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snipped-for-privacy@gmail.com wrote on 31/08/2018 :

..and some used resistance wire in the mains lead in place of a dropper.
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On Saturday, 1 September 2018 17:19:45 UTC+1, Harry Bloomfield wrote:

curtain burners are rare though. They were all miniatures.
NT
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On 01/09/2018 17:19, Harry Bloomfield wrote:

More recently that method has been used so the girlies can use their originally US made hair straighteners on 240V, with consequent overheating when they are used with the lead wound up.
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Max Demian

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On Fri, 31 Aug 2018 12:18:56 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

When I was a lad, I was given a transformerless radio. The chassis was connected to the mains live, rather than to the neutral. Whether it was meant to be like that or just that someone had wired the plug the wrong way round, I can't remember, but I discovered it the painful way when trying to set up an earth wire to the chassis!
--

Chris

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