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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 5th Sep 2010, 1:20 pm   #1
SuperHert
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Default UCH81 failed?

I have a radio with a UCH81, the valve has gone white. But not the getter flash, the actual glass has changed colour (see attached picture, it's not definitely not the light). The tube is still mostly transparent but you can clearly see the glass has changed colour. The radio this was fitted to has a problem were it can receive no signal yet it has a phonograph input which works fine (bar some hum). I have ordered a replacement valve but I don't want to ruin that one. I have tested all the transformers on the radio and there are no faults. Other than capacitors and this valve, I can't see anything wrong. Basically is this a fault with valve? Was it caused by the radio? I don't remember the valve being this colour when I bought the set last month. The heater still works but without a valve tester I have no idea what condition it is in.

Thanks, David.
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Old 5th Sep 2010, 1:35 pm   #2
paulsherwin
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Default Re: UCH81 failed?

It looks as if the valve has lost its vacuum. This is sometimes caused by mechanical damage but sometimes there's no obvious explanation. You can safely fit a replacement valve.
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Old 5th Sep 2010, 3:15 pm   #3
geofy
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Post Re: UCH81 failed?

Quote:
Originally Posted by SuperHert View Post
The heater still works but without a valve tester I have no idea what condition it is in.

Thanks, David.
Wouldn't the heater burn out if the vacuum was lost, unless it has a very small leakage to air?
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Old 5th Sep 2010, 4:28 pm   #4
paulsherwin
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Default Re: UCH81 failed?

I've had valves which have lost vacuum and the heater still seems to be OK. I've no idea how long it would last being run in this condition though.
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Old 5th Sep 2010, 8:46 pm   #5
SuperHert
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Default Re: UCH81 failed?

The thing that threw me was that the getter is still silver and is not turning white or falling off; which is contrary to what every other guide said. Thanks for your replies, hopefully the set will be working once the new valve and capacitors arrive.
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