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Not sure where you get this. Byrith has a good discussion on the 'balance' of the two configurations. Those who used the concertina, like early Dynaco, all switched to the LTP for their later stuff.
Some of those that switched to LTP actually made more dist and needs more complex circutry. Comfortina is inherently symmetric as same current is drawn across plate and cathode resistors.
Got some examples of this?
Have you read Byrith's paper? I think it's on the Lundahl site as well as other places.
I can recommend Tubelab's SPP amp. I've built some el84 pp amplifiers before I built it, usually with ecc83 as input tube, but I was never completely satisfied with the sound, but Tubelab's with ecc81 input tube was absolutely great. Used Hammond "iron". Built it point to point, didn't use pcb. Easy amplifier to build...
So far, so true. But the source impedances of both outputs differ significantly, resulting in different high frequency rolloffs, hence harmonic distortions. In common with the rather limited signal swings and the non existing CMMR (= high hum susceptibility), I'd regard the Concertina a poor PI, just resulting from tube saving demands.
Best regards!
The loading is limited to the grid resistors of the power tubes as long as not overdriving ( getting grid current). Thus for hifi
this unequal impedances are not a problem.
Maybe the greatest advantage with concertina : no adjustment is needed, perfect where no advanced instruments are available. Tube changes does not affect balance.
Driving a overdriven guitar amp is where concertina will have sideeffects.
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Provided the power tubes are not overdriven, the source impedances will be identical (and very low) and the high frequency rolloffs will be identical. Distortion in the concertina is extremely low. It's a near-flawless PI provided it remains equally loaded.
Since the anode and cathode resistors are in series, whatever electrical thing happens at one, happens at the other.
We're talking hifi, so we stay away from grid current.
Furthermore, this thread is about driving pentodes, which have low Miller. I wouldn't expect HF problems driving those.
For driving triodes you probably need a stronger driver.
We're talking hifi, so we stay away from grid current.
Furthermore, this thread is about driving pentodes, which have low Miller. I wouldn't expect HF problems driving those.
For driving triodes you probably need a stronger driver.
When load impedances of both outputs are equal, output impedances of both outputs are equal.
I suppose the main downside of EL500/PL500 types is the socket, B9D, which is not so commonplace.
That was an interesting schematic with an ECF80!
This socket is called Magnoval and was common in Germany and many European countries from about 1965 on. Not so in Sweden? The PL500 was among the first tubes that featured it.
Thanks, MerlinB, for this very interesting read!
Best regards!
Thanks, MerlinB, for this very interesting read!
Best regards!
This is the quote from Byrith's document at ( https://www.lundahltransformers.com/wp-content/uploads/datasheets/amplifier_30wpp.pdf )
Merlin, I take it you are the Valve Wizard himself 😲
I need to take a very close look at your spells ...
but in the meantime, do you think your analysis would hold for a Cathodyne used to bootstrap the load on the i/p valve?
http://www.r-type.org/articles/art-296.htm
I remember a load of correspondence in WW denigrating this circuit which is hinted at by Bailey
http://www.r-type.org/articles/art-097.htm
Yes. That is clear.
This same discussion about the cathodyne took place some 10 years ago.