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#1
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PrimaLuna adaptive auto bias board
Anyone have a schematic?
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#2
Posted to rec.audio.tubes
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PrimaLuna adaptive auto bias board
On Aug 7, 1:21*am, Bret L wrote:
Anyone have a schematic? I typed in the heading of your post to Google and found lots of hits but no schematic, but then I only tried for 5 minutes. Maybe you will find the schematic is something Prima Luna wish to keep secret to stop anyone here, there, or any damn where from copying what must be a "trade secret". But I did see pictures of the auto adjust board and it is crammed with a much more complex circuit than the whole of the audio amp circuit and it has transistors and a multi-pin chip of goodness knows what kind. Unfortunately, I cannot condone the use of such gee whiz complex solid state junk included in any tube amp, although it is becoming more common as makers try to add in crap that really does not belong, or is terribly fragile, like the Prima L board or is needed if you wish to use an i-pod or computer digital signal feed. The design of biasing methods in many tube amps is the one thing that is most commonly treated with utter contempt by many makers including top brands like ARC, and its almost as though the designer wishes the owner to get all muddled up up and get the biasing wrong and then have have the amp fail and so the owner buys another. Or else the designer wishes the person adjusting bias risk his life measuring voltages across a hard to get to resistor in the anode circuits which are at +500Vdc. Or else the designer uses utter crap quality pots, etc, etc, etc. In the vast majority of tube amps there is no attempt to include a circuit which detects excessive Idc in any one or more output tubes and then turn off the amp automatically so smoke and a blown OPT is avoided. Servo circuits which adjust grid bias voltage to keep the Idc constant are rather useless like tits on a bull when a tube decides to become a bit gassy and conduct huge currents for awhile until melt down and a short circuit occurs. And the Idc varies hugely in class AB amps so adjusting grid bias voltage for constant Ik in AB op is utterly pointless, so whatever a maker tries in any attempt for intelligent bias voltage control/ adjustment it MUST allow Idc in tubes to increase with AB operation and the condition of fixed bias MUST be maintained where the amount of class AB much exceeds the first few pure class A watts, which is usually the case in most tube amps made now to get high output power for sales reasons. There are some simple ways to monitor bias condition and protect an amp at my website. NO opamps are ever used. Patrick Turner. |
#3
Posted to rec.audio.tubes
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PrimaLuna adaptive auto bias board
On Aug 7, 6:07*am, Patrick Turner wrote:
On Aug 7, 1:21*am, Bret L wrote: Anyone have a schematic? I typed in the heading of your post to Google and found lots of hits but no schematic, but then I only tried for 5 minutes. Maybe you will find the schematic is something Prima Luna wish to keep secret to stop anyone here, there, or any damn where from copying what must be a "trade secret". But I did see pictures of the auto adjust board and it is crammed with a much more complex circuit than the whole of the audio amp circuit and it has transistors and a multi-pin chip of goodness knows what kind. Unfortunately, I cannot condone the use of such gee whiz complex solid state junk included in any tube amp, although it is becoming more common as makers try to add in crap that really does not belong, or is terribly fragile, like the Prima L board or is needed if you wish to use an i-pod or computer digital signal feed. The design of biasing methods in many tube amps is the one thing that is most commonly treated with utter contempt by many makers including top brands like ARC, and its almost as though the designer wishes the owner to get all muddled up up and get the biasing wrong and then have have the amp fail and so the owner buys another. Or else the designer wishes the person adjusting bias risk his life measuring voltages across a hard to get to resistor in the anode circuits which are at +500Vdc. Or else the designer uses utter crap quality pots, etc, etc, etc. In the vast majority of tube amps there is no attempt to include a circuit which detects excessive Idc in any one or more output tubes and then turn off the amp automatically so smoke and a blown OPT is avoided. Servo circuits which adjust grid bias voltage to keep the Idc constant are rather useless like tits on a bull when a tube decides to become a bit gassy and conduct huge currents for awhile until melt down and a short circuit occurs. And the Idc varies hugely in class AB amps so adjusting grid bias voltage for constant Ik in AB op is utterly pointless, so whatever a maker tries in any attempt for intelligent bias voltage control/ adjustment it MUST allow Idc in tubes to increase with AB operation and the condition of fixed bias MUST be maintained where the amount of class AB much exceeds the first few pure class A watts, which is usually the case in most tube amps made now to get high output power for sales reasons. There are some simple ways to monitor bias condition and protect an amp at my website. NO opamps are ever used. Patrick Turner. Good design uses a resistor specifically intended to burn up in a high current condition in the cathode circuit. With transmitting tubes a light bulb is sometimes used. |
#4
Posted to rec.audio.tubes
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PrimaLuna adaptive auto bias board
On Aug 7, 11:57*pm, Bret L wrote:
On Aug 7, 6:07*am, Patrick Turner wrote: On Aug 7, 1:21*am, Bret L wrote: Anyone have a schematic? I typed in the heading of your post to Google and found lots of hits but no schematic, but then I only tried for 5 minutes. Maybe you will find the schematic is something Prima Luna wish to keep secret to stop anyone here, there, or any damn where from copying what must be a "trade secret". But I did see pictures of the auto adjust board and it is crammed with a much more complex circuit than the whole of the audio amp circuit and it has transistors and a multi-pin chip of goodness knows what kind. Unfortunately, I cannot condone the use of such gee whiz complex solid state junk included in any tube amp, although it is becoming more common as makers try to add in crap that really does not belong, or is terribly fragile, like the Prima L board or is needed if you wish to use an i-pod or computer digital signal feed. The design of biasing methods in many tube amps is the one thing that is most commonly treated with utter contempt by many makers including top brands like ARC, and its almost as though the designer wishes the owner to get all muddled up up and get the biasing wrong and then have have the amp fail and so the owner buys another. Or else the designer wishes the person adjusting bias risk his life measuring voltages across a hard to get to resistor in the anode circuits which are at +500Vdc. Or else the designer uses utter crap quality pots, etc, etc, etc. In the vast majority of tube amps there is no attempt to include a circuit which detects excessive Idc in any one or more output tubes and then turn off the amp automatically so smoke and a blown OPT is avoided. Servo circuits which adjust grid bias voltage to keep the Idc constant are rather useless like tits on a bull when a tube decides to become a bit gassy and conduct huge currents for awhile until melt down and a short circuit occurs. And the Idc varies hugely in class AB amps so adjusting grid bias voltage for constant Ik in AB op is utterly pointless, so whatever a maker tries in any attempt for intelligent bias voltage control/ adjustment it MUST allow Idc in tubes to increase with AB operation and the condition of fixed bias MUST be maintained where the amount of class AB much exceeds the first few pure class A watts, which is usually the case in most tube amps made now to get high output power for sales reasons. There are some simple ways to monitor bias condition and protect an amp at my website. NO opamps are ever used. Patrick Turner. *Good design uses a resistor specifically intended to burn up in a high current condition in the cathode circuit. With transmitting tubes a light bulb is sometimes used.- Hide quoted text - - Show quoted text - Yes, indeed the sacrificial resistor is one solution to protection rather than have fuses which may be difficult to obtain, eg, typically 200mA rated which offer some protection against catastrophic faults. But owners of hi-fi systems do not want to have to change a fuse where they will often choose the wrong value, say 2 amps instead of 0.2 amps. Nor do any of them ever want to pay a tech to solder in a replacement resistor. So the most convivial and civilised solution for the average hi-fi amp owner is active protection where nothing ever fuses, but the amp is turned off from the mains when the Ik rises above say 150mA for longer than 4 seconds. Simply turning off the amp and then back on again resets the amp. Such a scheme offers protection against turningup the volume with a shorted speaker cable, or when obe tube of a PP pair has an open heater winding leaving just one OP tube to struggle on as a very badly set up single ended tube which soon begins to conduct too much Idc. Quite a few of my customers have much appreciated the protection measures I offer in all my amps - no huge bills for OPT or PT. There are more ways than one to achieve protection. I like to limit inrush current needed to charge up big values of B+ filter caps by use of a resistor in series with mains and once B+ has risen to 3/4 of full working value the R is shunted by a relay. One will find that the mains fuse value can be much smaller then if no such timed inrush circuit is present. Thus the mains fuse will more likely blow if say one OP tube of say a total of 4 conducts 300mA in addition to the other 3 conducting 50mA each. But tubes can conduct 100mA for awhile until they lose all bias control and become saturated. The excessive Ia needs to be monitored, hence my use of applying ONE average value of bias to say 2 output tubes and then having a balance pot to trim dc current equaity plus a BJT long tail pair to make to LEDs glow equally when the Ik iof the two OP tubes is equal. For protection I have a 5VA auxilliary power trans giving +/- 12V rails for operating all the protect & delay & LTP circuits. One other simpler way is to monitor Ik and have an SCR which latches on with excessive Ik and pulls the B+ to ground through a rugged 220R which will overload the B+ rail causing the mains fuse to blow. This is the notorious Crow Bar solution, and the circuits can be operated by a +12V rail generated off the filament voltages. The mains fuse can easily be accessed and replaced. Usually there is no room to put an incandescent light bulb in series with a cathode to ground, and then it needs to be a high voltage rated type; it is a primitive non-solution, and ppl cannot buy old fashioned light bulbs in Oz now because they have been deemed to be greenhouse incorrect and the only globes are now compact flurescent types. Patrick Turner. |
#5
Posted to rec.audio.tubes
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PrimaLuna adaptive auto bias board
On Aug 8, 3:31*am, Patrick Turner wrote:
On Aug 7, 11:57*pm, Bret L wrote: On Aug 7, 6:07*am, Patrick Turner wrote: On Aug 7, 1:21*am, Bret L wrote: Anyone have a schematic? I typed in the heading of your post to Google and found lots of hits but no schematic, but then I only tried for 5 minutes. Maybe you will find the schematic is something Prima Luna wish to keep secret to stop anyone here, there, or any damn where from copying what must be a "trade secret". But I did see pictures of the auto adjust board and it is crammed with a much more complex circuit than the whole of the audio amp circuit and it has transistors and a multi-pin chip of goodness knows what kind. Unfortunately, I cannot condone the use of such gee whiz complex solid state junk included in any tube amp, although it is becoming more common as makers try to add in crap that really does not belong, or is terribly fragile, like the Prima L board or is needed if you wish to use an i-pod or computer digital signal feed. The design of biasing methods in many tube amps is the one thing that is most commonly treated with utter contempt by many makers including top brands like ARC, and its almost as though the designer wishes the owner to get all muddled up up and get the biasing wrong and then have have the amp fail and so the owner buys another. Or else the designer wishes the person adjusting bias risk his life measuring voltages across a hard to get to resistor in the anode circuits which are at +500Vdc. Or else the designer uses utter crap quality pots, etc, etc, etc. In the vast majority of tube amps there is no attempt to include a circuit which detects excessive Idc in any one or more output tubes and then turn off the amp automatically so smoke and a blown OPT is avoided. Servo circuits which adjust grid bias voltage to keep the Idc constant are rather useless like tits on a bull when a tube decides to become a bit gassy and conduct huge currents for awhile until melt down and a short circuit occurs. And the Idc varies hugely in class AB amps so adjusting grid bias voltage for constant Ik in AB op is utterly pointless, so whatever a maker tries in any attempt for intelligent bias voltage control/ adjustment it MUST allow Idc in tubes to increase with AB operation and the condition of fixed bias MUST be maintained where the amount of class AB much exceeds the first few pure class A watts, which is usually the case in most tube amps made now to get high output power for sales reasons. There are some simple ways to monitor bias condition and protect an amp at my website. NO opamps are ever used. Patrick Turner. *Good design uses a resistor specifically intended to burn up in a high current condition in the cathode circuit. With transmitting tubes a light bulb is sometimes used.- Hide quoted text - - Show quoted text - Yes, indeed the sacrificial resistor is one solution to protection rather than have fuses which may be difficult to obtain, eg, typically 200mA rated which offer some protection against catastrophic faults. But owners of hi-fi systems do not want to have to change a fuse where they will often choose the wrong value, say 2 amps instead of 0.2 amps. Nor do any of them ever want to pay a tech to solder in a replacement resistor. So the most convivial and civilised solution for the average hi-fi amp owner is active protection where nothing ever fuses, but the amp is turned off from the mains when the Ik rises above say 150mA for longer than 4 seconds. Simply turning off the amp and then back on again resets the amp. Such a scheme offers protection against turningup the volume with a shorted speaker cable, or when obe tube of a PP pair has an open heater winding leaving just one OP tube to struggle on as a very badly set up single ended tube which soon begins to conduct too much Idc. Quite a few of my customers have much appreciated the protection measures I offer in all my amps - no huge bills for OPT or PT. I dislike circuits that are only to defend from idiots. I think people who can not solder and read a schematic should be told to their face they have no business owning tube amplifiers. |
#6
Posted to rec.audio.tubes
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PrimaLuna adaptive auto bias board
Usually there is no room to put an incandescent light bulb in series with a cathode to ground, and then it needs to be a high voltage rated type; it is a primitive non-solution, and ppl cannot buy old fashioned light bulbs in Oz now because they have been deemed to be greenhouse incorrect and the only globes are now compact flurescent types. Surely you can buy the small panel lamps and automotive bulbs? We are not talking 100 watt house bulbs but small stuff. I won't allow CF in my house due to the mercury. There will always be some niche source like Avgas for tetraethyl lead. |
#7
Posted to rec.audio.tubes
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PrimaLuna adaptive auto bias board
On Aug 9, 10:12*am, Bret L wrote:
Usually there is no room to put an incandescent light bulb in series with a cathode to ground, and then it needs to be a high voltage rated type; it is a primitive non-solution, and ppl cannot buy old fashioned light bulbs in Oz now because they have been deemed to be greenhouse incorrect and the only globes are now compact flurescent types. *Surely you can buy the small panel lamps and automotive bulbs? We are not talking 100 watt house bulbs but small stuff. I won't allow CF in my house due to the mercury. There will always be some niche source like Avgas for tetraethyl lead. I agree, not all incandescent lamps will be phased soon but eventually they will all be gone because there are alternatives like LED lights etc.... An auto lamp is OK with 12V across it and this causes its resistance to rise but it is a non linear resistance, and not suitable for any part in an audio amp unless maybe for a primitive compressor operating at low voltages with speakers. In a cathode circuit a tube could easily blow the 12V lamp. Patrick Turner. |
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