• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

703A tube source?

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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
 
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.
 
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
 
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
 
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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