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BRSHiFi 12th April 2011 04:24 PM

KT120 Tube
I am curious how the KT120 tube sounds. I want to try making an amplifier with a pair. Here is a link to the curves. I am having trouble judging which graph is the ultra linear, as they are not labeled. The first one looks like it maybe a triode connected. The third could be the UL graph.

A KT90 is another option, the datasheet does not have UL curves either.

tinitus 12th April 2011 05:05 PM

EL156/KT88/6550/KT90 then KT120 Single Ended Amplifier D.I.Y

BRSHiFi 12th April 2011 05:11 PM

I mean a push pull ultra linear.

tinitus 12th April 2011 05:23 PM

I think it holds a link to Dynaco forum discussing new ST120 using KT120
its pushpull

rock4016 12th April 2011 07:48 PM

These are PP class A UL.
KT120 Oddblocks • DIY Audio Projects Forum

tinitus 18th April 2011 04:07 AM

here's another 'player'

Roehren - Nach- und Neubauten - KT120 (TUNG-SOL) von BTB

waltube 18th April 2011 02:21 PM

Just finished a p-p amps with the use of EL34 or KT120.
Good results, mainly in tetrode connection.
With 440 Vdc and 100 mA of bias for each KT120 (45 w anode dissipation) we got 50 wrms on 8 ohm and, until 25 w, it is in class A.
The distortion is very good; the phase splitter uses the ECC99.
With a particular out. trafo (3 ohm on secondary and 3200 a-a to primary) we measured about 72 w on 4 ohm (as mentioned, we got 50 w on 8 ohm).
I am preparing an article on an Italian magazine; in case I can send details.



smoking-amp 18th April 2011 03:50 PM

Those KT120 plate curves given in the Rohren-Nach-.... link sure aren't very reassuring. Worst I've ever seen.

revintage 18th April 2011 04:53 PM

Canīt make the Reply tools work for some reason.

These curves arenīt impressing either:

smoking-amp 18th April 2011 05:13 PM

Are all these jaggie kinks maybe an artifact of the curve tracers used? Lack of density of sampled points, or some psuedo random digital selection of the measurement points to avoid over heating the tube. So adjacent points are taken at different internal temps of the tube?

Could be some HF oscillation issue in the tube/tracer jig. I use stopper resistors and/or ferrite beads on the tracer pin leads (g1, g2 and plate) to avoid that.

Or maybe there is some hysteresis issue with this tube when traced with increasing plate voltage versus decreasing plate voltage. I have seen this hysteresis issue around the knees on some pentodes on my TEK tracer. But the kinks in all of the KT120 curves seem to be everywhere.

Another issue I see sometimes is decreasing emission or gm during a curve trace that seems to gradually collapse the higher current curves after I throw the tracer switch. Reversible and repeatable after letting the tube cool down again. Not sure if its due to emission dropping or some grid heating up.

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