...and this why comparison to an automotive gearbox is a poor analogy. It only translates well if the car is accelerating and decelerating all of the time, whereas a car doing a steady speed doesn't present any modulations to be transformed.
"We" understand how transformers work but the objective was to describe somehow to Mr Tubesaregreat, that an 8ohm speaker load IS a significant load to an output tube and that is because the turns ratio of the transformer windings multiplies up the load seen by the output tube twice. He can verify this for himself simply by entering "reflected load in transformer" or "reflected resistance in transformer" into Google and looking at the pictures.
The simple algebra should convince him that a transformer with a turns ratio of 20 will appear to transform his 8ohms at the secondary to present 3200ohms at the primary and this is where phrases like "it's 5k transformer" or "it's a 2.5k transformer" have their origin.
By all means drift around with analogies and doublespeak that need clarification or further explanation, but stick to basic physics if at all possible.
kind regards
Marek
"an 8ohm speaker load IS a significant load to an output tube"
Of course, you plot load lines (for the transformer + speaker) to design a tube amplifying stage, including the output stage.
We (or most of us) all know this.
https://wtfamps.com/load-line-calculations/
https://www.valvewizard.co.uk/pp.html
Of course, you plot load lines (for the transformer + speaker) to design a tube amplifying stage, including the output stage.
We (or most of us) all know this.
https://wtfamps.com/load-line-calculations/
https://www.valvewizard.co.uk/pp.html
That's what those gearboxes in cars are called-transmissions. They're basically mechanical versions of transformers, albeit without the mechanical equivalent of the isolation you'd get with an electrical one.
I agree, but also I think in the beginning of all that he was just ''trying'' to say that there is no normal anode load resistor with which a person could read across for a plate current/dissipation reading to ''match'' tubes with. Using the rated primary Z isn't going to get that since it's only good for signal loads. In a pinch you could use the primary DCR if one knows it.
Kay Piranha makes perfect sense, you are just trolling. What is the difference in a power tube and a preamp tube supposed to be? I have used 801s as preamp tubes, driver tubes in power amps and output tubes of power amps. I have used E55Ls in phonostages and in spud amps. There is no such thing as "preamp tube" and "power tube". There are triodes, tetrodes, pentodes, heptodes, .... with different dissipation ratings, mu, Ri, ...
In an output stage you could use an anode resistor as load and use a coupling capacitor to block dc into an ungapped matching transformer that then isn't bugged by dc. The "parafeed" arrangement.
This is not really true. AC is a change in voltage over time, and only this change in voltage can be passed by an electrical transformer. DC is not coupled to the secondary. A mechanical (gear-box) transformer (automotive "transmission", differential, etc.) can couple down to DC, but it obviously works differently. Same simple integral turns/gear teeth ratio though.
But neither (or other analogous systems like pneumatic, etc.) converts DC to AC.
All good fortune,
Chris
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Chris, the voltage swing and current direction in the output stage is similar to the output of a full wave rectifier before filtering. That is known by all as DC. If you were to put that varying full wave DC (single direction) through an output transformer you will get true AC (alternating polarity) on the secondary. The definition of DC is broader that just a fixed voltage and its current. Of course, a static DCV and its fixed current level will not cross to the secondary because it doesn't create a varying magnetic flux. However, explain the flat top and bottom of a square wave that gets passed to a secondary. That is DCV and DC, too. It only works well with feedback amps. Something to ponder.
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You're trying to redefine a well established term, but if you're happy, I'm happy for you.
All good fortune,
Chris
All good fortune,
Chris
But even if there was a physical anode resistor, you wouldn't measure anode current by measuring voltage drop across this resistor.
You'd have to hang the reference lead of the multimeter off the B+, potentially risky.
Everybody I know measures anode current by measuring across the cathode resistor which normally (but not always) referenced to ground.
If you try to measure temperature because there is no anode resistor, you're very confused.
Jan
Jan, no confusion, No power amp of 1930s designs and newer ever used an anode resistor on the power tube.
Tubesaregreat - if there is no confusion, are you happy that an 8ohm load sitting behind a transformer is equivalent to an anode load resistor of around 2500 to 5000 ohms as far as the power tube is concerned?
kind regards
Marek
kind regards
Marek
To build an output stage that isn't a cathode follower you need Rl. Rl can be generated by anything, a resistor where Rl is the same as the DCR of that resistor, a CCS, the reflected load impedance on the primary of a transformer, or whatever.
Post # 36. Parafeed has been mentioned. You just ignore examples that are contrary to your delusion.
Your hammering on the anode resistor also hides the fact that the temperature 'matching' is nonsensical.
Jan
No power tube using 250 to 500 volts would function beyond a few watts with a 2500 to 5K anode resistor