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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Hi all.
It appears that I need to fix three valve radios.
One F5G40A sort of works but only one channel of the record player. Radio is dead as a brick, so I suspect a bad EB91 double diode valve. The getter looks "fuzzy" so I suspect it is gassy.
Only other thing it could be is the switch, but this is a pain to get to. I have the service manual here, cost all of £1.99
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Nah wrote ...
Very rarely will vacuum tubes be at fault, most likely the 50 year old capacitors.
There was a substantial international industry in manufacturing replacement valves, which only started to fade out when thermionic technology gave way to semiconductors in the 1970s.
Great job lots of replacement TV valves are constantly being offered on ebay to this day, such was the scale of the industry needed to support a technology that often failed. ALL thermionic valves suffer from reduced emission as they age, a frequent cause of poor performance in old electronic appliances.
Senile electrolytics certainly should be inspected, but unless there is a strong indication of a particular fault, fault finding should be done in a systematic manner, by measurement, rather than by moving from one guess to the next.
Registered Member #3567
Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260
I think you misunderstoond me. When these things were NEW the tubes were at most fault. The electrolytes were brand new and mostly ok. However, as this thing has been sitting for 40 years, the tubes stay as good as ever, while the caps get moisture and start to die. Do you not agree?
I have restored many radios, and only a handful of them have had faults from bad tubes.
I have always replaced all papers and electrolytes, as they are only a ticking time bomb that will blow up in your face. (it has happened to me many times) Mica and ceramic, are ok, and I only replace them if there is a reason.
To end, yes, shotgunning random parts is NOT a good idea, but these parts are not random, they are known to fail, badly. If you don't have a tube tester, use a multimeter to at least check if the tube's filliments are good.
will provide all the datasheets you need.
Thanks!
Paul
To sum it all EVEN more, order replacement caps for the ele. and paper caps from a place like mouser or something. Electrolytes will be in a metal can, or a cardbord tube, and paper caps will be covered in wax. A model number would help us to find a schematic.
Registered Member #1886
Joined: Sun Dec 28 2008, 02:55AM
Location:
Posts: 73
I've restored a few old tube radios I found and I agree with replacing all the paper/electrolytic caps. Probably 95% of the time any problems you have are caused by rotten caps. Even if it IS a tube problem I'd still recommend replacing all the caps. It's not a matter of IF they fail, but WHEN. When they do fail they can blow up or do worse things like short internally and then ruin your tubes/burn up your power transformer/make selenium rectifiers burn.
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WTB:- Valves
