Well, Jan's off to the festival I think, so we'll have to wait for him but there's lots of stuff on specific threads back there in time. I dug up that post from this search with Wavebourn as author. If you remove that restriction you'll get lots from him, smoking-amp, Michael Koster, et. al.
sser2,
You said: "Here is another no-feedback pentode amplifier, from the times when people were ditching their 2A3s for 6L6s."
I am not convinced.
Your attached article of the metal 6L6, and Kenyon transformers is when very few people had more than an AM / Shortwave radio,
And most did not have a Hi Fi.
At that time, not very many people threw out their stuff to get new stuff.
Now, many decades later, we belong to a throw away society.
Just my opinions.
You said: "Here is another no-feedback pentode amplifier, from the times when people were ditching their 2A3s for 6L6s."
I am not convinced.
Your attached article of the metal 6L6, and Kenyon transformers is when very few people had more than an AM / Shortwave radio,
And most did not have a Hi Fi.
At that time, not very many people threw out their stuff to get new stuff.
Now, many decades later, we belong to a throw away society.
Just my opinions.
All done many years ago but for different reasons, Any common AA5 receiver had something like a 35L6
pentode output with unbypassed cathode bias resister. So it looked like a good current source. Didn't matter much,
the speakers & cabinet were junk for the mass market. But still a good kitchen radio.
Kinda like Henry Ford's Model 'T' car.
Back in the day I hot rodded a couple for use with external speakers. Big improvements are easy to get.😀
All you had to do to “improve” one was get the bass resonant frequency between 60 and 80Hz. Bigger speaker 😀. Higher, and it sounds “boxy” like a kitchen radio. Lower, and it misses the range where the energy peaks in the kick drum and electric bass. Get it right, and it makes a one watt amp ”sound” like 20 with pop/rock music of the era.
We tend to dismiss everything before "Hi-Fi" as low fidelity. But such view is overly dismissive and condescending. The quest for sound quality began with the beginning of sound reproduction. There were giant leaps comparable to FM and LP: Victor's process, WE' s electric recording and condenser microphone, Rice and Kellog dynamic speaker, RCA's superheterodyne, Ferranti audio transformers. The process was continuous, there is no borderline between "before Hi-Fi" and "after Hi-Fi".
6L6 may be regarded as one of these leaps. In comparison with 2A3, it provided more power with less distortion. It was a step forward from existing pentodes like Type 47.
Hi-Fi set arbitrary parameters of sound quality, 20-20,000 bandwidth and 0.1% THD. Neither of these parameters truly reflects quality of sound reproduction.
I don't agree with the wholesale dismissal of everything before Hi-Fi. 78 rpm conveys the spirit of live music very well with quality sound reproduction, despite its technical imperfections.
Are you trying to imply that 20-20,000 bandwidth and 0.1% THD means lower quality of sound reproduction than, for example, 150-9,000 bandwith and 7% THD?! Or maybe equal sound quality?! Do bandwith and THD have any impact on qualilty of sound reproduction, according to you? What is the minimum acceptable bandwith and maximum acceptable THD to be called quality reproduction? Or maybe some other mistical property somehow magicaly overpowers any defficiencies in bandwith and THD?
I have asked you before, but you didn't give any answer - why do you think that current drive with tube amplifier with minimum 0.8% of third harmonic distortion plus supposedly zero THD from current drived speaker (total of 0.8% third harmonic) will have better sound quality than ordinary solid state, negative feedback amp with 0.001% THD voltage driving good quality speaker with 0.2% third harmonic distortion (total of 0.201% third harmonic distortion)? Is audio signal with 0.8% third harmonic distortion equal, better or worse in sound quality compared to 0.201% distortion?
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I just wonder, is air really lineaarly compressing? If so, then why is there in small closed boxes such a thing as distortion do to air compression?
air compression is still rather linear. the potential issue with small boxes is that the effective volume gets modulated by the driver cone motion. The effective spring stiffness of the air is inverse to the volume so volume modulation results in stiffness modulation. However, the cone area Sd factors in as Sd squared. in most cases the Sd modulation using conventional half rolls is the biggest source of stiffness modulation. Sd modulation is further exacerbated by the high pressure. Purifi’s neutral surrounds are effectively taking the Sd modualtion down.
a further aspect is that the stiffness modualtion is not causing wide band intermodulation. Stiffness affects mainly the bass but is not modulating the higher frequencies where the cone is mass controlled. Sd modulation is OTOH modulating reproduction of all frequencies.
The box air stiffness modulation is not only a factor for sealed boxes but also in reflex and PR/ABR.
cheers
Lars/Purifi