Indeed, a strange choice for output tube. With very low amplification factor, it will need a driver capable of 100+ VRMS at low distortion to realize its output capability.
A higher impedance implies a lighter load (lower mass) thereby a higher amplification factor and higher distortion.
The main problems of the amplification of the audio signal - setting a limit of what is achievable regardless of device technique
1) Exponential physical relationships
2) Inverse relationship between power and bandwidth
3) Depletion of mass
The very best of tube amps in history used capacitor coupling in dozens.
This aint bad per se, maybe you used the wrong coupling caps or false values.
The earlier way of amp building by using interstage transformers have its own technical problems, and direct coupling isn't always possible.
Its a continously repeated fairy tale that capacitor coupling is bad *** design.
This is perpetuation of trolling.
What you should do is to take some time to study and measure what's in your statement that is measurable, learn from that, then come back.
Could you please give a few examples of the very best tube amps in history?
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In Nature everything occurs at the expense of something else, we trade electrical properties for other electrical properties. Enthusiastically submitting what is being gained without recognizing what is being lost is naive self-deception. There is a price to pay for the efficiency of the push-pull pentode amplifier.
Capacitors are less harmful than magnetic components. Good quality output transformers are rare and expensive.
Capacitors are less harmful than magnetic components. Good quality output transformers are rare and expensive.
Fascinating read, esp. for including european stuff along US. Most are transformer-coupled. Only Klangfilm used capacitors all the way through. Interestingly, later WE, while using capacitors in upstream stages, still kept transformer coupling to the power stage.
I disagree. Capacitors have drawbacks too as dielectrics have hysteresis and lag like magnetics.
A parafeed solution for SE is inferior because the magnetic circuit is less linear and it's zero-crossing all the time. To reduce this unwanted behaviour exotic and more linear core materials are necessary but the rather big cap is still there leaving a seriously reactive load at low frequency despite frequency response and other less important aspects. That is the rather high price to pay for smaller size and/or high inductance. Not worth IME unless economy is important so exotic materials are out.....
Good quality output transformers are not rare at all. They are not cheap but that is also because it's a small market.
Highly reactive load at low frequency offered by LC coupling almost invariably results in higher distortion despite the inductance is higher respect to a proper and gapped SE transformer....try it out! Those cases where it can be equal or better it starts to be expensive too and having 2 components to do the job of one is still questionable.
If parafeed as never become a popular solution, not even when the quality of caps improved dramatically, there is a good reason....
If parafeed as never become a popular solution, not even when the quality of caps improved dramatically, there is a good reason....
Sowter makes good parafeed transformers with 30% Mumetal core but they are not cheap at $250 each!
SINGLE ENDED OUTPUT TRANSFORMERS
And a good cap still needs to be added. Is it worth? No, IMHO.
SINGLE ENDED OUTPUT TRANSFORMERS
And a good cap still needs to be added. Is it worth? No, IMHO.
I see it nearly the same way, but to engineer and produce a exceptional good quality (and I don't write here about Sowter, love their transformers but thei are middle class when it comes to sound output quality) is extremely difficult. It has to deal with many goals that couldn't be maximized all, so there have to find out compromises. And thats the reason, why there is only very few of those transformers are in the top notch class, many are in the middle class and thousands are in a low quality reproduction class.
The parafeed transformers instead can be optimised for handling only the music signal while the anode choke has to handle the full anode current and the signal transformer sees only the AC signal, not the DC load. That is a significant step forward for optimizing and stretching out the borders of transformer design data and leads towards, smaller, more perfect signal transformers for a much lower price in fact.
In the end, it couldn't be made such a statement as: parafeed is always more worse than direct anode load transformers. In most cases, with good designed circuits, parafeed will catch up with direct loaded transformers, and when it comes to price they often are the technical better and cheaper solution.
What this parefeed design idea keeps it in the shadow of all direct transformer loaded tube design is the fact that it needs more components, is therefore more difficult to calculate, not as famous as direct coupled designs and can not catch up to the low prices of low quality, direct coupled output transformers that many people deal with, especially when it comes to the asian El Cheapo transformers. But those people, who design with them and going the cheap and easy way, never experience a good engineered parafeed system. Like everyone in DIY else, they claim to have build world class, because its their own build and their own effort and they are proud of it. World class its nearly in none of those cases, its just their own middle class or low class design which could often be beated by parafeed, but never gave the chance to proofe this to be true.
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They are not the same at all. The supply does not form a second order filter like the output cap does. Reactive load at low frequency no good.
And 3mF is a big cap anyway. It is in the same class for losses as the 100 mF. Anything above the 1mF limit is usually lower quality than smaller values....
I disagree. I have top notch output transformers, not necessarily expensive because I can design them have have them made. If one cannot do that just buys good transformers that are not rare at all.
The good thing about output transformers is also that do not lose too much value over time. Everything else does.
And capacitors are as bad as magnetics. It's just that their drawbacks are ignored. They have hysteresis and losses.
Last but not least the plate inductor is in parallel and also leaving his footprint. CCS has drawbacks too.
I repeat that if parafeed would offer a more convenient solution it would have already become the standard at least in more commercial sectors of tube world. But it hasn't.....
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