UF41 Valve Failure Bush DAC90A

[bobhowe]

Hi tried out one of my Bush DAC90A to see what stations ( Or Lack OF Them ) None LW and 1 on MW Talk Sport thinking I might get better results on MW I tried out the Car radio and the same result only 1 when a got back in the house the DAC90A that I had left playing Talk Sport had gone quiet took the back of to have a look and the UF41 valve had gone down to air ( top of the valve had gone white ) . Took a UF41 out of another set and it works fine . Why has the UF41 gone down to air ? as it must have been ok when I switched the set on any suggestions ? kind regards Bob

[ppppenguin]

Valves occasionally go to air for no good reason. B8A types such as the UF41 can be damaged all too easily when extracting them from the spring grip found in some valveholders.

Recently I recovered the valves from a couple of Tektronix scopes that were only fit for scrap. (I know that's a horrible thing to do but these were truly beyond redemption) A number of valves, ordinary B9A and B7G types, had gone to air, possibly in part due to cold and damp storage.

[Geordie McBoyne]

Hi Bob,
gone down to air is common with all glass valves but it might be a good idea to take a look at the condition of the valveholder. It's possible you'll find a crack in the glass around one of the pins.

Geordie McBoyne.

[bobhowe]

Hi Jeffery thanks for reply the valve holders in set have not got the spring clips as some DAC90As don't know if it was perviously stored as you suggested before I got the set . Hi David what should I look at the valve holder for condition ? I could not see the if there was any cracks in the glass round the valve pins as it fell to bits when removed the valve . should I get a replacement valve with a metal skirt ? kind regards Bob

[boater sam]

DrStrangelove says its due to the cold and damp, he may well be correct.
I have had B8A valves where there is a crack in the button between 2 pins too.

[DrStrangelove]

DrStrangelove  says its due to the cold and damp, he may well be correct.
I have had B8A valves where there is a crack in the button between 2 pins too.

Er, that's merely what I've read elsewhere of course.

[Geordie McBoyne]

" should I get a replacement valve with a metal skirt ? kind regards Bob"
Hi Bob,
the metal skirt Mullard and Philips B8A base valves are now quite scarce and were made only for a few years after the introduction of the series in 1947.
The failure of your UF41 valve was a rare occurrence.
Mazda B8A base valves had a metal skirt. The 10F9 has different base connections.

From the Radiomuseum: https://www.radiomuseum.org/tubes/tube_uf41.html

The Mazda 10F9: https://www.radiomuseum.org/tubes/tube_10f9.html

Geordie McBoyne.

[bobhowe]

Hi David seen a nice metal skirt RT branded UF41 valve that should do the job kind regards Bob

[Mike Watterson]

I think the metal skirt only helps if there is a tight spring. I often take off the spring clip.

[Murphyv310]

Hi
I think you are getting paranoid that you'll have another failure Bob. These valves and other all glass valves go to air even in storage so no worse in or out of the radio. Remember the metal skirted versions will be older too and possibly no more reliable than a late one. I've had metal skirted ones go to air and perhaps there was a reason to go to all glass, one thing happened to me with the metal skirted version was that it was stuck fast with corrosion and the valve cracked right across the join and metal when I tried to remove it. Personally I don't think they are any better.