PL84 triode

TV-Roehre-PL84-Telefunken-m--Raute-ID1497-1497

The PL84 pentode is very well known out there. I’m not going to write about it as there is plenty of information about the use of this pentode in push-pull amps, etc as well as comparisons with the EL84, EL86 and Russian equivalents such as 6P14P, 6P15P and 6P43P. I recommend you to check Klau’s work here.

I have a nice set of Telefunken PL84 which I may be using in triode mode as part of a Spud project I’ve been working on the design for some time. I’m interested in triode-strapped curves but also will be looking at tracing the Schade-feedback curves when I get the time to do so.

I quickly found a sample valve that was close to the pentode specs at 90%. Good enough for my purpose so I proceed to trace the triode curves quickly in uTracer.

I should have traced the curves beyond 200V, but the 6 curves traced are good enough to generate an accurate triode model. A different story is developing a pentode/tetrode model as you may be aware of.

PL84-triode

The triode model can be easily generated:

PL84triodemodelThe spice Pl84-triode-spice model is very accurate.  The only disadvantage of this valve is the maximum 250V anode voltage which limits the available output power in a push-pull design compared to other similar valves like 6P14P, etc.

With a 5K Zaa transformer you can get 7W in class A1 with a distortion a bit higher compared to 6P15P but not that much:

PL84 PP Zaa=5K A1 7W

An extra 1.5W can be obtained if we use a 3K transformer instead:

PL84 Zaa=3K A1 8.5W

Author: Ale Moglia

"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp)

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