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Big Bad Bob Big Bad Bob is offline
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Default uTracer - tube curve tracer [kit]

On 09/01/16 13:57, Peter Wieck so wittily quipped:
On Thursday, September 1, 2016 at 3:25:19 AM UTC-4, Big Bad Bob wrote:


I've been kicking around the idea of making one of these that had ZERO
patch cables, and could efficiently deliver up to 0.5A for the plate (at
certain voltages), and at the same time, enough current for the heater
power. Some edge conditions for KT-series power tubes can conduct some
serious current (up to 1/2 an amp), and the heaters can suck up 12W or
so. If the power tube can't deliver it's max current at the correct
plate voltage, it's essentially "going bad".

anyway, that's somethi

but yeah, this particular curve tester goes up to 200ma which probably
covers most tng that an emissions-only tester wouldn't be able
to test for.ubes.


That would be labor-intensive as you would have to have the sorts of selector-switches that conventional tube-testers use to cover all the base options.


electronically, yes. but here's the beauty of it: design ONE such
switch, replicate it 12 times [for compactrons, need 12].

the patch bay on the uTracer does exactly that (from the schematics and
other indirect info on the web site). I would want to eliminate the
patch bay.

Additionally, if you control voltages to the pins, you can run the tube
through a series of tests, such as interelectrode shorts [both cold and
warm], open heater, etc.. You could do 'megger' style testing [i.e.
high voltage microamper conductivity testing] to detect partial shorting
at particular voltages, or perhaps detect gas contamination, based on
tube specs.

I envision the project as having 5 or 6 simultaneous source voltages to
put on a pin (plus "no connect). So 3 bits to assign it, per 'circuit'.
repeat that circuit 12 times, one for each pin, then connect 12 wires
to a 'bus' (basically) that wires up all of the sockets. Some
labor-intensiveness making that, of course, but I'd expect that with
switches or even patch plugs.

the 5 or 6 simultaneous voltages would include ground, heater (which
should be adjustable to either a positive or negative DC value, with a
possible high frequency injection to detect cathode signal from the
heater circuit), 'ground through a current measurement' (for cathode
current, etc.), B+ voltage, G1 voltage, G2 voltage, and possibly a 3rd
grid voltage for testing pentagrid converters. (all of those would be
software adjustable via PWM or similar, and would have scalable current
measurements built in).

all of them could be switched using IGBTs, MOSFETs, and or bipolar
transistors. So the idea would be to build a single circuit capable of
assigning 'one of these' voltages, with a digitally regulated "power
bus" supplying them.

anyway I built THIS already [which intentionally provides up to 400V for
tube circuits as well as +/- 0-12V which works well for a heater supply].

http://mrp3.com/sftpowersupply.html

I've used it to experiment with the idea of digitally regulating
voltages for tube amplifiers, mostly so you can vary their
characteristics - like maybe building ONE amplifier that can vary all of
the operating parameters. You might want to similate a tube rectifier,
or a solid state power supply, to get different sound characteristics.
One reason to use a tube rectifier is the voltage drop at max power -
when you play a guitar through an overloaded amp with a tube rectifier,
you get a kind of 'attack/decay' effect up front when you hit the
strings, due to power supply voltage dropping considerably from the 'no
power' to 'max power' transient. a digital power supply could simulate
this with full control over the decay time and amount of droppage.

anyway, I've been kicking ALL of these things around for a while, long
enough that I'd almost be happy just to see SOMEONE do it as I lack even
a REMOTE chance of being able to fund any of this kind of engineering,
but it has a nice geek factor and so I'd like to see it done.