At first glance, it's AB UL with no NFB, so probaly not as good as the designs I mentioned earlier. Triode the KT's, and drop their B+ a bit to put them in class A and add say 10% cathode FB and you'd be close. However, the implementation of the design is at least as important as the design itself.kacernator said:
Look at the schematics of the 47 P-P or the Tabor on my web page. Both amps use DHPs - Directly Heated Pentodes. The amps use local feedback on the output stage and CCSs on both stages. Very nice sounding amps but not simple projects.
After the 47 was up and running I never looked back at SE again.
400V, 80mA/tube, fixed bias, about 7ka-a (not too fussy 5-8k) for nominal load, ie 8R or 4R speaker.kacernator said:I am sorry, but I am totaly lost in those tons of technical text.
Can you just give me the right primary impedance?Thank you.
The ECC99 fromt end previously shown may not have enough gain for many applications.
kacernator said:
I am sorry, but I am totaly lost in those tons of technical text.
Can you just give me the right primary impedance?
The 'right' load is a not a single number until you've described the rest of the details of the power stage. either way, to achieve class A, the power tubes need to stay 'on' the whole timie. Brett's operating point will allow a +/- 280 V swing( 3500R * 0,08Amps ). When operating in Class A, each tube works into half the a-a load.
Pick the operating point, and see where the load line goes. Pentodes will be able to swing a greater percentage of their B+ compared to triodes( w/o running into grid current ).
cheers,
Douglas
I dont know if anyone reads this thread these days but i agree with what you wrote... my personal experience has been that without the distortion( not massive ugly kind) the SE amps wud have sounded boring.in my own homebrew SE amp a simple addition of feedback ruined the otherwise different sound. My son too noticed it. he said the amp sound dull and boring when the NFB was added .i just couldnt see the merit of risking playing with 300V dc to make an amp that sounds like a clean chip amp. i havent built a push pull but i heard its much true to actual sound so i assumed it wud be kind of boring too... but everybody has their own choices..i simply like the SE tube amp for its different sound and tone/distortion etc. I bought Miniwatt N3 and it sound good... but there a huge HF roll off which makes it sound dull to my ears. My own homebrew SE tube amp sounds far more alive to my ears.other than that i wud go for any amp that renders the mids like real life and forward. My SE amp seemed to do that always. so much more fun for so less. AND.. i would love to have schematics of an PP tube amp thats sounds really LIVE.... personally speaking...my ideal would be a hybrid amp with the tone that u get in a SE tube amp...i just dont like the 300v dangerous dc and the super heavy transformers so much.
BR
Amit
50 SHADES of AMPLIFIER
For a NON boring P-P amplifier, build a class A P-P amplifier using big TV sweep tubes, using low B+ (low enough for the class A mode, and low enough for triode operation of the tubes).
On each P-P side, provide switches to configure the individual output tube as UL, triode, or shunt Fdbk "Schade" mode with an adjustable Fdbk pot.
On one P-P side provide a switch to disable the AC drive to the tube (leaving the tube as a DC biased current source effectively to balance the OT).
Then provide an (un-) balancing gain pot in one (or both) sides of the (2 tube) driver stage to unbalance or balance (continuous selection) the AC gain going to the output tube grids (for single pot, use the side with the AC drive disable switch).
You will need some grid bias pots and two cathode current sensing meters to DC balance the output stage in the different configurations possible. Or, better, use a cap bypassed CCS under each output tube cathode to automatically achieve DC balance. (leave in the cathode current meters, so auto balance can be seen to settle)
Recommend putting spark HV arrestor devices, or HV MOVs, across each P-P OT primary section (to CT) for protection of the OT during switching and no load conditions. (primary sides can reach 2X B+ normally, somewhere above that should be clamped)
Play with the options and dials for 50 shades of coloration. (no, not Hifi, except for a few combinations)
An adjustable, zero to low global N Fdbk pot could be interesting too.
A speaker disconnect switch should be used during switching of the option switches. To avoid pops.
Could provide multiple output tube sockets on each P-P side, wired for different (reasonable) tubes. Switch select the active tube by an enable/disable of the screen grid voltage (screen to cathode connected for off). Dissimilar tubes in P-P are allowed with the auto DC/CCS balance scheme, use a grid AC gain control (ie, driver balance controls) on each driver side then to allow for different tube gains.
..
For a NON boring P-P amplifier, build a class A P-P amplifier using big TV sweep tubes, using low B+ (low enough for the class A mode, and low enough for triode operation of the tubes).
On each P-P side, provide switches to configure the individual output tube as UL, triode, or shunt Fdbk "Schade" mode with an adjustable Fdbk pot.
On one P-P side provide a switch to disable the AC drive to the tube (leaving the tube as a DC biased current source effectively to balance the OT).
Then provide an (un-) balancing gain pot in one (or both) sides of the (2 tube) driver stage to unbalance or balance (continuous selection) the AC gain going to the output tube grids (for single pot, use the side with the AC drive disable switch).
You will need some grid bias pots and two cathode current sensing meters to DC balance the output stage in the different configurations possible. Or, better, use a cap bypassed CCS under each output tube cathode to automatically achieve DC balance. (leave in the cathode current meters, so auto balance can be seen to settle)
Recommend putting spark HV arrestor devices, or HV MOVs, across each P-P OT primary section (to CT) for protection of the OT during switching and no load conditions. (primary sides can reach 2X B+ normally, somewhere above that should be clamped)
Play with the options and dials for 50 shades of coloration. (no, not Hifi, except for a few combinations)
An adjustable, zero to low global N Fdbk pot could be interesting too.
A speaker disconnect switch should be used during switching of the option switches. To avoid pops.
Could provide multiple output tube sockets on each P-P side, wired for different (reasonable) tubes. Switch select the active tube by an enable/disable of the screen grid voltage (screen to cathode connected for off). Dissimilar tubes in P-P are allowed with the auto DC/CCS balance scheme, use a grid AC gain control (ie, driver balance controls) on each driver side then to allow for different tube gains.
..
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Top switch: (put power supply up top, and On-Off switch)
Bottom switches and dials: SE distortion modes (amplifier down bottom)
Maybe we should start a new thread. Let everyone design it.
Or, could just start with a shunt Fdbk "Schade" amplifier, like Pete's 50 Watt Monoblock, and add on the bells and whistles.
Provide sockets for 300B, 26HU5/26LW6, 6CB5/6DQ5, 21LG6/6HJ5
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Also butting in here long after everything has been well explained; perhaps something on the 'acceptability' of music that I have not seen here (if I recall correctly!):
It may be old hat that not all 'distortion' is sounding badly. E.g. adding everything to a piece of music (here I lean more to the light classics and such) converted to an octave higher and mixing a little bit into the original, will make much music sound 'warmer', 'more full', more pace, body .... recognise those terms? I can certainly imagine some music which will sound better that way.
Point: Everything an octave higher (i.e. second harmonic) can never be strident/false (speaking normal music terms!). Similarly I have read that 3rd harmonic 'distortion' (a 'soh' an octave and a fifth higher) does not produce a particularly pleasant tone combination, but also not immediately sounding strident. (I have read that some 5th harmonics addition can make wind and string instruments sound more 'crisp'.) Not going into the effect of still higher order odd harmonics (7th and 9th can generate listener fatigue and harsh sound even when added in very small quantities) for now; just to indicate that music sounding 'pleasant' for some might actually have benefitted from added distortion thataway.
[I recall reading an anplifier ad years ago stating: "Just the right amount of distortion has been added to make the music pure" .... (at least some back-handed honesty in that ad ....)]
Adding furthermore how differently music is 'interpreted' by different individuals' hearing*, and it becomes hard to categorise say amplifiers simply through impressions gained by hearing. It becomes quite clear why some people will prefer e.g. S.E.T. designs. In this respect there is then a distinct difference between high fidelity as per the dictionary's definition of 'closest to the original', and simply personal preference.
_______________________________________________________
*In the field of human hearing, consulting e.g. the work of Dr. Diana Deutsch et al will be an eye-opener regarding how easy it can be to 'bluff' the hearing faculty!
It may be old hat that not all 'distortion' is sounding badly. E.g. adding everything to a piece of music (here I lean more to the light classics and such) converted to an octave higher and mixing a little bit into the original, will make much music sound 'warmer', 'more full', more pace, body .... recognise those terms? I can certainly imagine some music which will sound better that way.
Point: Everything an octave higher (i.e. second harmonic) can never be strident/false (speaking normal music terms!). Similarly I have read that 3rd harmonic 'distortion' (a 'soh' an octave and a fifth higher) does not produce a particularly pleasant tone combination, but also not immediately sounding strident. (I have read that some 5th harmonics addition can make wind and string instruments sound more 'crisp'.) Not going into the effect of still higher order odd harmonics (7th and 9th can generate listener fatigue and harsh sound even when added in very small quantities) for now; just to indicate that music sounding 'pleasant' for some might actually have benefitted from added distortion thataway.
[I recall reading an anplifier ad years ago stating: "Just the right amount of distortion has been added to make the music pure" .... (at least some back-handed honesty in that ad ....)]
Adding furthermore how differently music is 'interpreted' by different individuals' hearing*, and it becomes hard to categorise say amplifiers simply through impressions gained by hearing. It becomes quite clear why some people will prefer e.g. S.E.T. designs. In this respect there is then a distinct difference between high fidelity as per the dictionary's definition of 'closest to the original', and simply personal preference.
_______________________________________________________
*In the field of human hearing, consulting e.g. the work of Dr. Diana Deutsch et al will be an eye-opener regarding how easy it can be to 'bluff' the hearing faculty!
Linear low µ DHT when works into OPT >10x RI, can handle the transformer itself. Without any FB, & with negligible high order distortions.
This is the problem of many people, chasing every mW (choosing lowest OPT- impedance and adding GFB), which is just stupid. Go transistor instead...
Phase distortion is real thing.(GFB)
Hmmm… sounds to me mostly like the dynamic bidirectional link between speaker-cone physics, amplifier output damping, total drive power and the electromagnetic 'mass' of output transformers is what people are hearing as "the sound".
Well, if you like it, go with it!
Its not like it matters.
You're only either arguing with yourself from a perfection-is-king basis,
Or you're arguing with fellow aficionados and geeks…
Which is always a questionably sane activity.
Flame wars.
Over damping, push-pull, linearity, feedback, monocrystalline copper, you name it.
All of THAT starts edging into the Snake Oil forum.
GoatGuy
Well, if you like it, go with it!
Its not like it matters.
You're only either arguing with yourself from a perfection-is-king basis,
Or you're arguing with fellow aficionados and geeks…
Which is always a questionably sane activity.
Flame wars.
Over damping, push-pull, linearity, feedback, monocrystalline copper, you name it.
All of THAT starts edging into the Snake Oil forum.
GoatGuy
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