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In Reply to: RE: 2a3 and 6B4G amps and tubes - favourites? posted by andy evans on October 13, 2021 at 00:55:47
Tough to answer Andy.
It depends on operating points. Some folks say the 2A3 types are slightly more linear and better sounding than 300Bs. Run the curves with different loads and you will quickly find it is easier to build low distortion, 3.5W 300B amp than 2A3 amp. And there are plenty of flavours of each to satisfy... perhaps more flavours of the 300B. That said, I run 2A3 at non-classical operating points and like them.
I'm moving on to the PX4. Then the EML 1605. Too many quality tubes out there to limit one's self to 2A3 and 300B types.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Follow Ups:
The usual 250v, 60mA, -45v sounds great to my ears. Do you run the tubes hotter?
There's quite a variety of monoplates, some looking like 300b plates. Hard to know how hot to run them. They don't give curves and operating points for the different sub-types. Just the usual curves on Franks.
I'm using 6C4C. May be possible to run them hotter but there's only anecdotal references. They sound great at book OP.
Book operating points in tube manuals were designed for antique radio sets and industrial applications.
Not always the best data sets for high fidelity audio reproduction.
DT667
I've said this before - you can't speak of operating point without including the load impedance.
For example, the book operating point is 250v/60mA/2500 ohms and has very similar distortion, damping factor, and power performance to 300v/50mA/4000 ohms. Swap the load impedances and they are suddenly very different.
I like a higher voltage relative to current: a higher rp operating point. 50mA/300V or 42mA/250V with 4k2 loads. I've wanted to try 60mA or even 50mA/350V for the 300B or higher dissipation 2A3 with a 5k+ load, but am moving on to something else with lower distortion.That is just my limited experience and preference and I totally get people liking something different.
Lots to try and learn.
Edit: in line with Paul's post above, I've included the load impedance for the various stated operating points.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Edits: 10/13/21 10/13/21
Most forms of distortions that are meaningful
musically, occur when a power supply lags in
timing the power that a tube is drawing on musical peaks,
and then adds insult to injury while it tries to
recharge its filter capacitors WAY TOO SLOWLY.., interfering
with musical flow all the way.
Most tubes, if run conservatively, are very forgiving
as to voltages-- as long as you stay clear of max. limits
as published for the tube BRAND and BATCH that you're using.
Current-wise, tubes stay very linear as far as reproducing
music goes-- less so if you're obsessing over published measurement
recommendations instead of listening. Amps that are called
upon to run at maximum power levels will stress vacuum tubes
unless they're run at quite a bit less than published
current recommendations. This will apply to all small
amps with less than 10 watts of output power with most
speaker loads and SPL's normally wanted in the listening room.
It is very smart to experiment with these values as long
as both voltages and plate currents are very conservative.
Experiment with speaker loading, and output transformer
primary impedances. You're in for some big surprises.
-Dennis-
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