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Old 20th September 2009, 06:29 PM   #1
MannyE is offline MannyE  United States
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Default 703A tube source?

Anyone know a source for these? I need two for an amplifier project.
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Old 20th September 2009, 07:16 PM   #2
gianis is offline gianis  Greece
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Default 703a

http://www.tubedepot.com/nos-703a.html
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Old 20th September 2009, 09:07 PM   #3
316a is offline 316a  England
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Originally Posted by MannyE View Post
Anyone know a source for these? I need two for an amplifier project.
Don't bother ! These are a real P.I.T.A to use . If you find some which have been handled roughly , the filament can break in transit , incidentally the filament draws in excess of 4a . 50% of these that were in my stock had translucent rather than brown getters , a good proportion were also gassy . These do look pretty when fully functional and sound ok but I don't believe the 703a is anything special . The worst thing about the 703A is that the valves lose emission very quickly if running with a few mA or more . Avoid strain on the pins at all costs also !!!

316a
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Old 21st September 2009, 12:09 AM   #4
MannyE is offline MannyE  United States
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Originally Posted by 316a View Post
Don't bother ! These are a real P.I.T.A to use . If you find some which have been handled roughly , the filament can break in transit , incidentally the filament draws in excess of 4a . 50% of these that were in my stock had translucent rather than brown getters , a good proportion were also gassy . These do look pretty when fully functional and sound ok but I don't believe the 703a is anything special . The worst thing about the 703A is that the valves lose emission very quickly if running with a few mA or more . Avoid strain on the pins at all costs also !!!

316a
Thanks for the advice! Actually I was aware of the limitations, but I became intrigued with peter millet's "glowing hybrid amp" and decided to give a go to building one. I have the board he designed and most of the components needed, so now all I need is a pair of unmolested tubes.

He wrote that he wanted it to sound something like a 300b amp, and I am curious to find out if he pulled it off.
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Old 21st September 2009, 12:46 AM   #5
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Originally Posted by 316a View Post
The worst thing about the 703A is that the valves lose emission very quickly if running with a few mA or more
316a
I've seen two versions of 703A's - one has a getter, one does not.

The one with the getter I've had no issues running at low current for some time. The ones without - and that includes the WE variation, I forget the number - 358A? - need to be run with the plate glowing.

Pete
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Old 21st September 2009, 01:07 AM   #6
316a is offline 316a  England
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Quote:
Originally Posted by pmillett View Post
I've seen two versions of 703A's - one has a getter, one does not.

The one with the getter I've had no issues running at low current for some time. The ones without - and that includes the WE variation, I forget the number - 358A? - need to be run with the plate glowing.

Pete
Interesting that there is a non-gettered version but I guess it's going to be pretty useless 3C24 is a nice easy to use 'full cherry' type , British versions by EEV and Elliot take a lot of abuse before the anodes begin to glow though . I have some WE388A which have a triangular slab of carbon for an anode . These also appear to have the emission problem as the 703A which is a shame as these test very much like a type 10 . 316A is a good one , you can get good sounds at around 10mA and not too difficulkt to mount , again this type loses emission quickly if driven hard .

316a
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Old 5th October 2009, 07:12 AM   #7
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Hi

I just bought some 703A's off Radio Electronic Supply (which Peter kindly pointed me to) for my version of Peter's Glowing Amp.

Will post my results once I've built them...

Rgds.
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Old 15th November 2009, 02:33 PM   #8
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Good info on this thread. I have some WE 368A's without the getter and planned on using them as a driver for a bigger tube. With the low filament voltage AC heating doesn't sound like it should be a problem? For sockets I used some press in turret sockets from Mill Max in a teflon disc. Not exactly idiot proof but there are no small children around. To cover the pins coming out the top I plan on another small piece of teflon to fit over them.
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