Hi Peter.
The oscons brought about the balance I was looking for (more bass and lower midrange) in my preamp, with much more clarity than I had previously experienced with other electrolytics, but I was also not 100% satisfied with the sound at first, feeling that there was a slight loss of "air", but do bear in mind that they require a LOT of running in. They are sounding better and better in my system and the "magic" is returning. My wife keeps commenting on how wonderful the music sounds and that is always my best barometer. However, if you have sufficient lower frequencies without them, they may not be necessary in your system.
Regards,
William.
The oscons brought about the balance I was looking for (more bass and lower midrange) in my preamp, with much more clarity than I had previously experienced with other electrolytics, but I was also not 100% satisfied with the sound at first, feeling that there was a slight loss of "air", but do bear in mind that they require a LOT of running in. They are sounding better and better in my system and the "magic" is returning. My wife keeps commenting on how wonderful the music sounds and that is always my best barometer. However, if you have sufficient lower frequencies without them, they may not be necessary in your system.
Regards,
William.
Thing about the comparison is the tubes are completely different, a choke for a 1P1L is going to be much much smaller than one for the #26. On paper the 4P1L just looks supperior with its 1.5k Rp vs 5k Rp.
Of course the wildcard is that extra screen and microphonics.
My guess is one could find an excellent condition #26 that sounds better than a poor condition 4P1L and vice-versa. So the question often comes down to which tube can I obtain in good quality. Lately is seems all the #26's have been culled, with the broken microphonic ones being the ones for sale, not sure what the supply of 41PL's looks like.
Ri (i=internal) is the same, maybe you haven´t heard of it
? Ra is also another accepted shortform.
For lowest distortion the 4P1L needs to be driven at about 20mA, so that rules out a choke suitable for 26. I was thinking on testing the 4P1L loaded with a CCS or gyrator instead.....
If it helps at all, I am running circa 25mA through mine with plain resistor plate loading and led biasing (5 red led's. Started with 6 but needed more current so shorted one out). Cant give exact plate voltage off hand - it is somewhere between 160 and 180v. You do need plenty of current or they sound thin, but use too much and they sound a bit heavy. They are plenty cool at this OP. I can hold the glass in my fingers without burning myself. "Just cruisin'"
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Ri (i=internal) is the same, maybe you haven´t heard of it
I thought "i" always referred to current. Never too old to learn.
Having successfully completed the 26 preamp, now I'm looking to complete the belated 4P1L on a very low budget. So will go for a gyrator loaded stage and filament bias. Have a filament supply of 18V and HT supply of 170V on my current preamp, so will force my design to use this.
Will aim to get to 20mA and around 100V of anode voltage as the quiescent point. With a 15 ohm / 3W filament resistor can get to that point based on my simulation. Also the attached circuit performs as with a 150H choke loaded one.
I take I need to build this up to see how it performs and how microphonic ends up!
Any suggestions?
Will aim to get to 20mA and around 100V of anode voltage as the quiescent point. With a 15 ohm / 3W filament resistor can get to that point based on my simulation. Also the attached circuit performs as with a 150H choke loaded one.
I take I need to build this up to see how it performs and how microphonic ends up!
Any suggestions?
Attachments
My suggestion is to build and check for microphonics. I am hundred percent sure that everything else will be exceptionally perfect, but I can tell nothing about microphonics: I never used 4P1L tubes n preamps. I personally, however, would parallel filaments, to squeeze the last drop of non-linearity from it, for expence of current.
Just for laughs I measured the distortion on a few #26 and 4P1L (with a IXCP10M90S load). Guess which had the lower distortion.
I did Take some measures time ago and 4P1L was much better than 26! Is really linear in triode mode
Anatoly, I chose this gyrator as current is higher than 10mA. Although I will etch next weekend your version for my 45 SE driver...
With a bit of time will build this...stay tuned, hopefully before Christmas!
Cheers,
Ale
Why both filaments in parallel will increase linearity?
In that case will be a bit more power dissipated by the filament regulators, so won't be a big issue...
Thanks
I did Take some measures time ago and 4P1L was much better than 26! Is really linear in triode mode
Yes, same as my tests. Will it sound better than the 26? That I don't know.
What happens when you connect in parallel many little triodes that are identical to each other, but have slightly different bias voltages?
Well, that is precisely what I want to find out. I now have a 26 preamp which as it stands it will be really hard to beat as it sounds superb, so will be able to do a proper listening comparison...
Didn't think it that way
yes two triodes in parallel will have lower distortion albeit not sure the impact of slightly different bias?
Perhaps you could think of each point on the filament as representing a phantom triode running at a slightly different OP due to the voltage gradient across the filament. (This is what Wavebourn hinted at in an earlier post)
If you operate the filaments in series the active area of the filament represents a much larger voltage gradient and with some types this may also concentrate the emission in one region of the filament if the gradient across the filament is appreciable compared to the grid bias. My suspicion is that indeed the linearity with the filaments operating at 2V in parallel might be better than the 4V option in series.
In AC filament the point of peak emission travels across the filament length with the progression of each cycle - this has minor implications for filament life since DC operation does not exhibit this trait. (The hum with AC operation in a line stage application would probably be unacceptable.)
If you operate the filaments in series the active area of the filament represents a much larger voltage gradient and with some types this may also concentrate the emission in one region of the filament if the gradient across the filament is appreciable compared to the grid bias. My suspicion is that indeed the linearity with the filaments operating at 2V in parallel might be better than the 4V option in series.
In AC filament the point of peak emission travels across the filament length with the progression of each cycle - this has minor implications for filament life since DC operation does not exhibit this trait. (The hum with AC operation in a line stage application would probably be unacceptable.)