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In Reply to: RE: Transformer Interaction - Fact or Fiction? posted by PakProtector on April 07, 2021 at 17:59:39
unlike the other guy I know who's played around with a lot of transformers. :)
I see a few patterns from these tests I posted above. (and have a few questions)
1- the lower impedance transformers seem to measure well
2- dynaco seemed to compromise other parameters in the names of pretty square waves
3- peerless seemed to have compromised square wave performance for other parameters
A quick glance at this would tell me I'd prefer my dynaco Z565 to my peerless S265. That is not the case from listening.
Is the square wave performance an important measurement in evaluating a transformer?
Why are lower impedance transformers not popular given that they seem to do well in both HF extension and square wave measurements? typical recommendations I see always are more primary impedance for less distortion and a small sacrifice in power output.
Follow Ups:
A lot depends on how and what you enjoy
listening to, and what are the speakers?
I have built and serviced many tube amps over the
years-- most of them push-pull.
I like to hear clean, fast, accurate, on-time dynamics.
I like detail also, but will not sacrifice the above to get it.
I have found (not all for the same reasons,
but as a generality that happened in MOST cases),
that I liked tubes run at low plate dissipation levels,
and that loaded heavily with a very low-DCR, lower impedance
primary of the output transformer.
Understand that I will not listen to Negative Feedback-- it
destroys musician intent.. I have never had my hands on a tube
amplifier that was not drastically improved (musically) by
getting rid of its FBK loops.
Basically, I like an amp that acts like great Solid-State,
but has the best "tube" qualities also... and I don't
mean overly smooth or slow in timing by this-- or "nicer"
to listen to, What I mean is better rendition of music..
a sense of true presense.
This taste of mine necessitates that I pay attention to
measurements and note the theories and measurements that
are out there, but it also means that I will break any
rule anytime I can get better performance and reliability
by doing so.
Your questioning the theory that light (high-DCR, high
primary impedance) loading of an output tube that is run
according to design-center values, while it will give the
best measurements, might NOT sound the best, is VERY well
taken.
In fact, by-the-rules kinds of amps never sounded
excellent to me, but a few did sound just OK.
This observation can be applied both to old tube
equipment, and also to the very latest.
To sum up: run a tube near the bottom 1/3 of its plate
power curves, but don't go TOO far with this-- find out,
instead, what you can get away with. If you get too close
to the bottoms of those curves, you will get much less
low-distortion power.
So, the question is how much power delivers the best sound
from the speaker that you are using? What are the effects on
THAT SPEAKER when you make the tube more linear by going
closer to design-center values. How MUCH BETTER will it
sound if you run at LESS plate dissipation and LOWER
impedance (heavier loading) on the tube?
What does your speaker NEED?
Question everything they tell you. They're not wrong.
They are usually right--- about something-- . BUT there
is a better-- much better-- world out there to be had.
You'll have to find those op. and loading points by trial--
and you should also find out if some brands of tubes agree
with what you're doing, and maybe others don't. It is VERY
difficult to know how a given tube will behave when operated
outside of it's approved design-center values.
But you can find that out-- "try look?". It's your call.
-Dennis-
Just keep in mind the test rig John Atwood used for this testing. I talked to him about this one year at The Mill, and we agreed that driving the secondary with a set source impedance( a SS amp and series resistance equal to that of the prescribed loading) with a resistive load across the primary would have yielded much better results. So for an example OPT, a 5k to speaker, putting 2.5k across each half of the primary, and with the 16R tap driven, a 16R series resistor to effectively set the driving impedance( counting the SS amp as zero output Z ) would be the preferred way to accomplish that.
The in-circuit performance would be quite difficult to 'apples to apples' given the radically different loads applied vis a vis the tube characteristics set by their plate and g2 supply. Since there is no way I'd set up a tube circuit the same for a 3.2k load as I would a 10k load, it would be best to use another test procedure. Either tune the tube voltages for the load, or get rid of the tubes entirely. The latter is certainly a lot easier... :) and delivers compare-able results between the various OPT's tested.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
thanks!
The audio and power transformers in the picture are oriented 90 degrees (laminations) to the power transformer and that is correct.
The OPT is 90 degrees from both choke and power. Power and choke are the same orientation. I pulled the choke cover plate to confirm.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
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