Earspeakers Posted March 14, 2015 Report Posted March 14, 2015 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?
Craig Sawyers Posted March 14, 2015 Report Posted March 14, 2015 On my list of must-buys is this http://dos4ever.com/uTracer3/uTracer3.htmlat Euro 210 (about equivalent to USD) as a kit. Now I have more valve (tube) testers than I know what to do with, but none of them have the capability of the uTracer.
Earspeakers Posted March 14, 2015 Author Report Posted March 14, 2015 Brilliant, just what I was looking for. I didn't want to buy an old smelly tube tester again, the tracer is perfect. Hm, is there anything that a regular tester will measure that the tracer doesn't?
Craig Sawyers Posted March 14, 2015 Report Posted March 14, 2015 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.
chinsettawong Posted March 14, 2015 Report Posted March 14, 2015 That tube tracer looks like a good buy. It's so very tempting.
PretentiousFood Posted March 14, 2015 Report Posted March 14, 2015 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.
Earspeakers Posted March 14, 2015 Author Report Posted March 14, 2015 (edited) 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 March 14, 2015 by Earspeakers
insanity Posted March 15, 2015 Report Posted March 15, 2015 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.
Earspeakers Posted March 15, 2015 Author Report Posted March 15, 2015 (edited) 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 March 15, 2015 by Earspeakers
spritzer Posted March 15, 2015 Report Posted March 15, 2015 Not counting the few thousand units in stock at Mouser?
Earspeakers Posted March 15, 2015 Author Report Posted March 15, 2015 Not counting the few thousand units in stock at Mouser? Dunno the specifics. Do you know the operating point of the BHSE & Megatron EL34s, 400VDC or below?
insanity Posted March 15, 2015 Report Posted March 15, 2015 Another option for a tube tester would be this one: http://www.ebay.com/itm/VACUUM-TUBE-TESTER-LCD-DISPLAY-LAMPEMETRE-ULTRA-COMPACT-/251165653561?pt=FR_Image_son_Autres&hash=item3a7aa3ba39 Has less functions, is cheaper, but tests up to 450V.
kevin gilmore Posted March 15, 2015 Report Posted March 15, 2015 kgst, kgbh,kgbhse,kgdt and T2 all use constant current plate supplys as well as the srx revisited. So the tube tester would need to be modified because the resulting curves would be very diffent.
Craig Sawyers Posted March 16, 2015 Report Posted March 16, 2015 (edited) Well no - all you do is set a near horizontal load line at some high value corresponding to the effective resistance of the constant current source, and plot characteristics along that line. Edited March 16, 2015 by Craig Sawyers
Earspeakers Posted March 16, 2015 Author Report Posted March 16, 2015 I had it described to me as fixing the operating point due to the high effective impedance. A resistor lets the tube slop it's operating point around, but a CCS nails it to a point on the chart, which is probably why they sound so good.
Earspeakers Posted March 18, 2015 Author Report Posted March 18, 2015 Actually here's the best reference for Active Loads The active load is the red line, compared to the blue which is the usual resistive load. The curve spacing is much more even on the active.
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