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Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!

195.99.125.202

Posted by Thorsten on April 17, 2000 at 08:26:27

In Reply to: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!! posted by Dave VH on April 15, 2000 at 14:38:09:

Hi there,

First to say that I'll be adressing also a bit of the tailend of the whole previous, now archived discussion here.

All the time my MAIN argument was that compared on a level playing Field DHT's like the 300B are preferrable sonically to Triode connected Penthodes. And I feel the margin is not small.

That said, the design of the Amplifier has as much to do with the sound as the Valves used. I could think of a few 300B SE Amplifiers that make certain Ultralinear Push-Pull EL34 Amplifiers (like the Quicksilver) positively sound great.

So, only because an Amplifer has a DHT does not mean it's great and only because the output Device is a triode wired Penthode doesn't mean it's bad. This is not about the sound of a specific Amp but about how far we can stretch things.

Now to the criticism of my comparison. I feel first of all that it is not really valid.

If we observe the characteristic Data of an EL34 in Pseudo Triode Mode and a 300B, the Anode Impedances are quite close, as will be operating voltages and currents (try a EL34 at 350V and 60mA, it will sound quite decent). So identical Output Transformers can be used with no real sonic impact.

Secondly, valves where not "just plugged in", you cannot do that anyway. Sufficient care was taken on such items as the Cathode Bias resistors and the Heater Voltages, as well as an Increased +B for a similar operating point for the 300B despite the higher Bias Voltage. As said, an Output Transformer that works well for Triode Wired EL34's works well also for a 300B.

A Driver Circuit geared to driving PSE 300B's (in my case 6CG7; RC coupled to 5687; RC coupled to 300B or EL34) will actually have a much easier time driving the EL34 Grid with it's lower Capacitance and lower Gridleakage, so an EL34 Outputstage actually makes the Driver Circuit work less hard, so IF the sound is similar, the EL34 should sound better.

The outcome from this Experiment was quite conclusive. There is no comparison (on a level playing field) when EL34 (or indeed KT88 - they where tried too) is pitted against 300B. While it is perhaps not fair to extrapolate from the results of KT88 and EL34 to that of all triode wired penthodes, for the Question "Triode wired KT-88 or EL34 vs. 300B?" it is a quite conclusive answer.

I would also like to add that the EL34 equipped version is an exceptional Amplifier, which makes most of the Amplifiers I have had in my hands sound rather less than good. It's only that the 300B again is almost as much better....

So, I have no problems with people liking Amp's useing triode wired penthodes as output's.... I don't even have problems with people saying these are good amplifiers. No problem at all. I don't even have problems with people saying they like a specific Amp using triode wired penthodes better than a specific amp using DHT's.

I'm interrested only in pointing out that if you try to get the MAX out of a given Budget I feel that using 300B's over EL34 or KT88 as output Devices will at only a slightly higher cost go MUCH FURTHER, sonically speaking.

Later Thorsten

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