Its been a while since I designed anything and especially anything that worked first time, so I'm here to pick your brains.
My niece has recently moved on from hard drugs to diy audio. Yes really. So to keep her on track, I'm introducing her to thermionics and I figured a headphone amp is a good entry (and re-entry) project.
We need to get to 1v RMS and between 50 and 100mW to drive the usual crap digitally focussed headphones kids use these days. Typically 28 - 32 ohm nominal.
Source is likely to be mp3 device of some sort.
I have a stack of PCF80 triode/pentode bottles - aroundf 40 of them. I figure I can possibly get a headphone amp out of a pair of them. They go to 10mA/14mA and around 1.5W anode dissipation.
Low budget, I'm looking to use line transformers for opts, and a wall wart feeding a back to front small isolating step down transformer to supply B+ with isolation.
Audiophile is NOT the aim here. Learning is. With that in mind comment on the aim and the following topology proposals.
My niece has recently moved on from hard drugs to diy audio. Yes really. So to keep her on track, I'm introducing her to thermionics and I figured a headphone amp is a good entry (and re-entry) project.
We need to get to 1v RMS and between 50 and 100mW to drive the usual crap digitally focussed headphones kids use these days. Typically 28 - 32 ohm nominal.
Source is likely to be mp3 device of some sort.
I have a stack of PCF80 triode/pentode bottles - aroundf 40 of them. I figure I can possibly get a headphone amp out of a pair of them. They go to 10mA/14mA and around 1.5W anode dissipation.
Low budget, I'm looking to use line transformers for opts, and a wall wart feeding a back to front small isolating step down transformer to supply B+ with isolation.
Audiophile is NOT the aim here. Learning is. With that in mind comment on the aim and the following topology proposals.
Attachments
here are the specs of the pentode in triode mode, if it helps (data from Tom Schlangen).
µ: 44,5 ; gm: 5,2mA/V ; rp: 8,6K
found the curves on my hdd, couldn't find them on the web anymore.
µ: 44,5 ; gm: 5,2mA/V ; rp: 8,6K
found the curves on my hdd, couldn't find them on the web anymore.
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Sorry, a line matching transformer will need to be parafeed. As such only type 2 will work. I would attempt to run the pentode as a pentode to maximize the triodes modest mu of just 20.
Shoog
Shoog
Hmm that triode section looks a bit weak. Maybye use a cheap vertical deflection tube.😛
Do you happen to have some Pl36 tubes laying around ? Or perhaps PL84 500/504 or those are all capable of operating on a fairly low B+ due to the low Ri
The Pl output could then serve as a trioded cathode folower that is AC coupled to the headphones. Your PCF80 could then serve front-end.
For good data on the PL36 try the E235L datasheet, its the same tube but no plate cap😛
Do you happen to have some Pl36 tubes laying around ? Or perhaps PL84 500/504 or those are all capable of operating on a fairly low B+ due to the low Ri
The Pl output could then serve as a trioded cathode folower that is AC coupled to the headphones. Your PCF80 could then serve front-end.
For good data on the PL36 try the E235L datasheet, its the same tube but no plate cap😛
What kind of ratio does your line transformer have ?
Even using an ideal ccs and a 10k load, the triode doesn't make a very nice power tube. Sims best at about 90v/14ma.
What seems to kinda work in sims is using a µ-follower with the pentode on top. Triode at 5ma, pentode at 12ma.
Even using an ideal ccs and a 10k load, the triode doesn't make a very nice power tube. Sims best at about 90v/14ma.
What seems to kinda work in sims is using a µ-follower with the pentode on top. Triode at 5ma, pentode at 12ma.
thanks all - Ben, yes thats where I was leaning toward. Thanks for the triode curves too - I miss having access to Tom's work so easily.
Don't need a lot out of it remember, and the matching is just fiddling with the impedance ratios of the opt which has a pretty good range of options.
Alternatively, there is a local guy who can wind me some cheapish opts at a ratio I select, making options other than parafeed possible.
Don't need a lot out of it remember, and the matching is just fiddling with the impedance ratios of the opt which has a pretty good range of options.
Alternatively, there is a local guy who can wind me some cheapish opts at a ratio I select, making options other than parafeed possible.
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