Thanks to Marcus Gedanitz for his measurements. Röhrenkennlinien
Here's a EL34 at 60V
Here's a EL34 at 60V
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I'll second that. Once upon a time I used to use a 3300uf cap for a 6SN7 preamp. It would play for 2 minutes before it noticibly sounded bad. When I got bored enough to measure it I found it had dropped to 12V... It was designed for 375V!
Klaus has some various curves traced out on his site including a few low voltage ones. You'd be surprised how amazing a 6P43P looks at only 40V.
Russian Tube Tester Files - Instrumental Curves and more
Klaus has some various curves traced out on his site including a few low voltage ones. You'd be surprised how amazing a 6P43P looks at only 40V.
Russian Tube Tester Files - Instrumental Curves and more
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This is a nice thread. I hope that more members will share their measurements on vac.tubes running at low supply voltages. Because I have build a stereo headphone amplifier
running on 40V supply with an EL84 single stage for each channel and am not quite happy with its performance, I am re-designing it for use at 80V supply.
Here the measured characteristics for that supply range.
running on 40V supply with an EL84 single stage for each channel and am not quite happy with its performance, I am re-designing it for use at 80V supply.
Here the measured characteristics for that supply range.
EL86 is maybe much better for low supply voltage, because it is a "high current"-type pentode.
I have also done some tests with low voltage preamplifiers.
Here is one 6SN7 with 12 V + Ub. The tube is driven with positive Ug1 and with some grid current. It requires low impedance signal source, but nowadays all are such.
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That is only possible when the cathode heating is active
and there is NO anode voltage available for a long time.
But I must confess that I vaguely heard of this
phenomenon when I was getting my education in electronics (and that is a long,long time ago).
Will do a "search" on the internet though...
Really...?
120V dc is only safe until it manages to pass enough current through the wrong part of you... After that you probably won't care anyway.
There is a reason that the Low Voltage Directive stipulates safety requirements for AC voltages above 50 and DC voltages above 75.
I am not saying you shouldn't build it. Just that you should not assume that 120V dc is safe. It is only safe if you make it so.
Cathode poisoning comes from ion bombardment (IIRC?) and so will be worse at higher anode voltages and lower heater voltages.
Cathode interface comes from having a hot cathode and no cathode current, so it does not depend on anode voltage except to the extent that you need some anode voltage to get some anode current.
The usual problem with low voltage is distortion. Some people prefer this, which is why the internet is full of cheap Chinese 'tube buffers'.
Cathode interface comes from having a hot cathode and no cathode current, so it does not depend on anode voltage except to the extent that you need some anode voltage to get some anode current.
The usual problem with low voltage is distortion. Some people prefer this, which is why the internet is full of cheap Chinese 'tube buffers'.
The 6P43P looks good at 40V. Bottom of the page: Tube Tester Files - EL82, EL84, EL86 Soviet Clones
He says it looks like a 4P1L.
My small experience of running ECC88's at low voltage (50V) was that after a while they started to draw significant grid current because the bias was so low in order to get adequate current though them. This is a real problem if the grid is tied to a valuable pot which will be destroyed in fairly short order.
Cannot say for certain if this is a universal situation - but worth considering.
Its really not that difficult to generate a reasonable B+ cheaply that I never repeated the experiment.
Shoog
Cannot say for certain if this is a universal situation - but worth considering.
Its really not that difficult to generate a reasonable B+ cheaply that I never repeated the experiment.
Shoog
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