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Tube testing/testers for Stax amps


Earspeakers

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Staxen amps (at least the Mafia versions) use either el34 or 6S4 (with the Megatron including some 12's ...)

 

I sold my tube tester years ago after getting out of SET's and such. What do you all think about testing these tubes? Is there a simple test rig, perhaps even 'in circuit' we can use to test the tubes without having to deal with a full blown tester?

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Nope.  In fact the uTracer goes much further.  You can even put a load line on a set of measured curves and it calculates the distortion.  All the usual characteristics, u,gm,ra etc are measured for a chosen bias point.

 

I've just sent him a mail asking him to set one aside for me.  The Euro rate is really good for me just now so it is even more of a bargain.

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I got one a few months ago. It's fantastic for tracing curves, and the spice modeling works quite well if you want to try playing with weird tubes. It does a great job with pentodes and tetrodes, too.

One point of caution: the uTracer 3 is limited to 300V, and the 3+ to 400V. I haven't tried tracing an EL34 yet, but it might require an external filament supply. I haven't managed to trace anything at an instantaneous current greater than 200mA without tripping the circuit protection either, but that's probably user error. It will probably happen with an EL34 at higher grid bias voltages.

If you're using it strictly for stax amps, you might be better off with something else. gm will vary according to your bias, and the EL34 at BH bias is right at the edge of the tracer's capabilities. The quick test options aren't especially reliable, and the software is still a bit buggy, too. It's an extremely powerful platform, but not especially straightforward.

That said, I've been using it a lot for pentodes and it's been outstanding. For starters, I found out that most of mine suck, and that the ones I tested are startlingly out of spec.

One last thing- I would advise building it with some extra protection on the HV supplies. I accidentally reverse biased the screen supply when testing an inverted triode, and still need to repair it.

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One point of caution: the uTracer 3 is limited to 300V, and the 3+ to 400V. I haven't tried tracing an EL34 yet, but it might require an external filament supply. 

 

BH bias is right at the edge of the tracer's capabilities

 

I was just wondering about this. What operating point are KGST 6C4's and Megatron and BHSE EL34's at? 

Edited by Earspeakers
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The 6S4a is the Kgst runs at 340V. maybe someone else know about the bhse.

 

But if you get that tube tester which looks really nice, you should probably go for the 3+ version.

 

Definitely, but it's the only one for sale at any rate (I keep writing 6S4A wrong for some reason)

 

I'm on the list for the next run, he's drained the world supply of 450V/100uF caps apparently ...

Edited by Earspeakers
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