I guess because of market trends. Many tube amplifier fans, especially SET fans, prefer a passive speaker, probably a fullrange one
This is very valuable information to me. So, there may be little to no value in pushing a SE output tube to 90-100% dissipation, especially if not using an output transformer specifically designed for the current, if I read that correctly.
Please define driving impedence. I'm trying to keep my terms straight in my head as I learn.
Last edited:
https://www.diyaudio.com/community/...s-lets-think-big-see-big.312699/#post-5195240
It's not just an autoformer, the windings are transmission lines with varying line impedance, varying from Zin to Zout. The final step in optimization is to use a tapering width strip of metal with each winding as one turn. so that each winding is bifilar with the previous winding, and bifilar with the next winding. But the previous and next turns are NOT bifilar with each other. The whole assembly has magnetic cores over it to increase inductance for low frequencies.
It's not just an autoformer, the windings are transmission lines with varying line impedance, varying from Zin to Zout. The final step in optimization is to use a tapering width strip of metal with each winding as one turn. so that each winding is bifilar with the previous winding, and bifilar with the next winding. But the previous and next turns are NOT bifilar with each other. The whole assembly has magnetic cores over it to increase inductance for low frequencies.
Last edited:
50AE,
Passive versus Active speaker systems?
Bi-wired versus non bi-wired speakers?
There are popular commercial loudspeaker systems that do not have bi-wired capable input connectors.
There are commercial output transformers, both push pull and single ended that have a very adequate, or excellent frequency response
(of course, they are mid-priced to very expensive).
"Cheap is Not Good, Good is Not Cheap", Frank Reps, Gordon Rankin's Baby Ongaku design, Sound Practices Magazine
There are those who have lots of money to spend on their audio playback systems . . . $$$
There are those who prefer not to modify, nor not have someone else modify, their favorite loudspeakers, to make them bi-wireable.
That is a fair percentage of the audio playback systems market.
And then there were, and are, those who have plenty of money, to pay someone else to make them an audio system, or a component of an audio system that meets their desires.
Saul Marantz was a good example.
SET fans have used many types and topologies of loudspeakers. The same goes for push pull fans.
Passive versus Active speaker systems?
I am sure there may be a model, or models, but I am un-aware of a loudspeaker system that uses any vacuum tube amplifier inside the loudspeaker cabinet.
(Exception: guitar amplifiers; but this is the Tubes / Valves threads [Hi Fi / Stereo], it is Not the Instruments and Amps threads).
If you want a complete amplifier-speaker self contained system, there are the Flat Plate solid state amplifiers, with the heat sink facing the air outside of the loudspeaker cabinet.
Practical, whether it sounds good, or does not sound good to some listeners.
Passive versus Active speaker systems?
Bi-wired versus non bi-wired speakers?
There are popular commercial loudspeaker systems that do not have bi-wired capable input connectors.
There are commercial output transformers, both push pull and single ended that have a very adequate, or excellent frequency response
(of course, they are mid-priced to very expensive).
"Cheap is Not Good, Good is Not Cheap", Frank Reps, Gordon Rankin's Baby Ongaku design, Sound Practices Magazine
There are those who have lots of money to spend on their audio playback systems . . . $$$
There are those who prefer not to modify, nor not have someone else modify, their favorite loudspeakers, to make them bi-wireable.
That is a fair percentage of the audio playback systems market.
And then there were, and are, those who have plenty of money, to pay someone else to make them an audio system, or a component of an audio system that meets their desires.
Saul Marantz was a good example.
SET fans have used many types and topologies of loudspeakers. The same goes for push pull fans.
Passive versus Active speaker systems?
I am sure there may be a model, or models, but I am un-aware of a loudspeaker system that uses any vacuum tube amplifier inside the loudspeaker cabinet.
(Exception: guitar amplifiers; but this is the Tubes / Valves threads [Hi Fi / Stereo], it is Not the Instruments and Amps threads).
If you want a complete amplifier-speaker self contained system, there are the Flat Plate solid state amplifiers, with the heat sink facing the air outside of the loudspeaker cabinet.
Practical, whether it sounds good, or does not sound good to some listeners.
Last edited:
This is another way of describing the R in your initial question, discussed through post #13. To be (hopefully) clearer, low frequency response of an OPT is modeled as a series resistor R and shunt inductor L, a simple single pole (6dB/oct) high pass filter. The series resistor R is imagined as a parallel of the output valve(s)' contribution and the reflected load's contribution. The L is the OPT's primary or "magnetizing" inductance.
Both the R and the L vary with signal level, and the L varies in other complicated ways, but the model itself is very good. It's only the reality of iron cored inductors that gives us any complications. But the RL model is always good. Does that make any sense?
All good fortune,
Chris
Last edited:
Sometimes learners like me need to be refocused on the point. 😉
Yes, it makes sense. I haven't fully digested it yet, but it makes sense, and I do understand RL. Thanks.
Last edited:
Transformers for tube audio is a complex mix of physics.but there are no shortcuts.you want good sound, open to interpretation, one gets what you pay for. There are transformer manufactures who have been doing audio for years and the ones who are still manufacturing are doing somethin
Right. As the experts say its as much about science as it is about art. Good sound soothes the soul.
Still on the topic of low frequency extremes, primary inductance varies because the iron core's inductance varies linearly with its permeability, a measure of how well the core concentrates magnetic field compared to air. And permeability, in turn, varies on a curve called the B/H curve which plots analogs of field strength vs. electrical current. The slope of this curve is
permeability.
Sorry, I can't figure out how to post this right. This curve is duplicated in reverse and upside down for current in the other direction. Push-pull amplifiers have DC currents balanced against each other at idle, so idle at the lower bottom corner. This is a static curve, ignoring hysteresis, which is a difference between the actual path with current increasing and current decreasing.
But anyway, for the gruesome details of low frequency modeling you'll want to explore the B/H curve. Note two things about the mu (permeabilty) curve above: first is that it falls above a knee in the B curve, called saturation. And second that it also falls at very low levels; there is a flat spot through zero crossing. The burble through zero crossing is significant for push-pull amplifiers, because that's where it operates at idle and small signal. But a single ended amplifier idles up on the high slope leading edge of the B curve, and swings at large signal from down towards zero crossing to up near saturation. When 50AE talks about idling current, this is the limitation that he's addressing. Idling too far up the B curve gets you too close to the saturation end of the curve.
All good fortune,
Chris
But anyway, for the gruesome details of low frequency modeling you'll want to explore the B/H curve. Note two things about the mu (permeabilty) curve above: first is that it falls above a knee in the B curve, called saturation. And second that it also falls at very low levels; there is a flat spot through zero crossing. The burble through zero crossing is significant for push-pull amplifiers, because that's where it operates at idle and small signal. But a single ended amplifier idles up on the high slope leading edge of the B curve, and swings at large signal from down towards zero crossing to up near saturation. When 50AE talks about idling current, this is the limitation that he's addressing. Idling too far up the B curve gets you too close to the saturation end of the curve.
All good fortune,
Chris
I needed to know that. Without overcomplicating it, how in general do we choose a starting point for the idling current of a SE amplifier given that we have to pay attention to the transformer not just the tube? How do we get in the ball park? For purposes of further simplifying discussion, let's stick with ordinary SE transformers with M6/Z11 EI laminated cores. Just a basic core for now, no specialty materials or designs. If you want an example to use, as I mentioned the SE amplifier is pentode, global negative feedback from the 8 Ohm output (I want to move it to the 4 Ohm) with EL34 output tubes.
Last edited:
Only at low frequencies do we need to worry about primary inductance, and primary inductance is only really hard to get for single ended amplifiers, and that's only because the B/H curve must be flattened (rotated clockwise) deliberately with an air gap, and that's only to reduce the core's contribution to permeabilty, and that's only desired to soften the bend of the knee approaching saturation. It's all about the B/H curve at low frequencies.
A side note, because primary inductance is harder to get for single ended amplifiers, and pentodes require more of it for the same response (see your RDH4 chart above), pentodes are not an ideal choice.
All good fortune,
Chris
A side note, because primary inductance is harder to get for single ended amplifiers, and pentodes require more of it for the same response (see your RDH4 chart above), pentodes are not an ideal choice.
All good fortune,
Chris
Given all of that, to bring it all together, how about a real-world example that I can relate to one of my current projects?
Here is a Hammond SE output transformer that might make a good example: https://www.hammfg.com/files/parts/pdf/1630SEA.pdf
Here is a Hammond SE output transformer that might make a good example: https://www.hammfg.com/files/parts/pdf/1630SEA.pdf
Never Get Old,
I am attaching a discussion of the Hammond 1635SEA.
I hope that helps you understand some more about the tube and output transformer interaction.
I am attaching a discussion of the Hammond 1635SEA.
I hope that helps you understand some more about the tube and output transformer interaction.
@6A3sUMMER that attachment is perfect. For me, seeing an actual example makes all of the theory come together in my head. I can't thank you enough. 🏆
There are a couple of points on the short summary on page 54 that need correcting,
The difference in calculated & measured unloaded Z is more probably caused by iron core losses in parallel with the primary inductance.
With pentode driving the primary, with proper secondary loading the OPT spec of 3500 Oms would be used in the calculation. 👍
The difference in calculated & measured unloaded Z is more probably caused by iron core losses in parallel with the primary inductance.
With pentode driving the primary, with proper secondary loading the OPT spec of 3500 Oms would be used in the calculation. 👍
In general, how do we approach this problem? In other words, how do we pick a realistic, ballpark value to start with?
I still use the information in my text books of >60 yrs ago.
Amps were never my day job, just a hobby. 60 yrs a P.Eng this coming Jan 23rd,
Think I will listen to Benny Goodman & The Rolling Stones on Vinyl,
And demolish a couple glasses of red wine. 👍
Practically and generally, we would choose an existing manufactured product based on reputation. An expert like 50AE will study and experiment for years, but we won't be able to do that. The builder's judgement of maximum idling current should be respected just as much as his/her judgement about choices and details of winding, air gaps, layering, etc.
All good fortune,
Chris
All good fortune,
Chris
Some off-the-shelf models don't specify, especially low budget choices or ones from (gasp) China. So that's why I asked how to approach it in general.