Example: +-15 supply SEclassA 1.7A bias with load 8ohm
@ idle;
idle current: 1.7A => idle power= 1.7A*(15+15)V =51W
@ (+/-)10V(peak) sine output;
I(peak) out= (+/-)10V/8ohm = (+/-)1.25A(peak) I(rms)out= 0.89A(rms)
power consumption = (15+15)V * 1.7A + 0.89A*15V -0.89A*15V =51W (the same with idle)
Note: 1.85Abias will only give 14W to 8 ohm
TO3 is not help, lets say it has 2.3celcius/watt and isolator+heatsink has 2celcius/watt. Total will be 4.3celcius/watt.
Operating at 1.85A/6 = 0.31A and 40V.
Dissipated power will be 0.31*40 =12Watts.
Say the ambient is 25celcius, Tj will be 25+12W*4.3 = 76.6celcius, and derating power will be around 55%
It is 11Watts allowed and handle 12Watts = 70%~90% probability blow.
@ idle;
idle current: 1.7A => idle power= 1.7A*(15+15)V =51W
@ (+/-)10V(peak) sine output;
I(peak) out= (+/-)10V/8ohm = (+/-)1.25A(peak) I(rms)out= 0.89A(rms)
power consumption = (15+15)V * 1.7A + 0.89A*15V -0.89A*15V =51W (the same with idle)
Note: 1.85Abias will only give 14W to 8 ohm
TO3 is not help, lets say it has 2.3celcius/watt and isolator+heatsink has 2celcius/watt. Total will be 4.3celcius/watt.
Operating at 1.85A/6 = 0.31A and 40V.
Dissipated power will be 0.31*40 =12Watts.
Say the ambient is 25celcius, Tj will be 25+12W*4.3 = 76.6celcius, and derating power will be around 55%
It is 11Watts allowed and handle 12Watts = 70%~90% probability blow.
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I will try to explain simply:
To convert AC voltage and AC current to a DC equivalent voltage and current, we usually consider the wave of the AC voltage and current to be a pure sine-wave. (File:Sine and Cosine.svg - Wikipedia, the free encyclopedia). Graphically this means to take the bottom wave, flip it from bottom to top. So at this point you will have 2 "bumps" side by side. Then you cut horizontally the top of both "bumps" to fill the trough (or bottom part) so at the end you see a flat line. The height of this line is the equivalent in DC.
When you use math to do the same thing, you take half of the full AC wave and you divide it by the square root of 2 ( √2 ) to get the equivalent in DC. The meaning of RMS is root mean square which refers you to what we just calculated.
Now regarding the power: With DC voltage and current you multiply the voltage by the current and you get the power in watts so: 1 Volt x 1 Amp = 1 Watt
For AC power you need to multiply 1 Volt RMS x 1 Amp RMS to = 1 Watt
If you stick to the theory 1 watt RMS does not exist because once you have "normalized" your AC Volts and Current and multiply them you have an equivalent in Watts...period.
What is used in the industry of audio is another matter!
I would refer you to this site for more reading on the subject!
Audio power - Wikipedia, the free encyclopedia
I hope I was not to boring
🙂Eric
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Hi Eric, you have many big heatsink, they could easily handle more than 300W for 70celcius design, and your transformer looks like hundreds watts rated, that still possible to reach 70W class-A.
Note again: loudspeaker with 8ohm nominal impedance may reach 32ohm and normally 10ohm or 12ohm.
Note again: loudspeaker with 8ohm nominal impedance may reach 32ohm and normally 10ohm or 12ohm.
Morning All.
I see we have all finally reached an accord, that's nice, the forum works.
A bit more info for Kingfisher.
Way, way back in the mists of time, even long before my time, there was this new thing electricity, which entrepreneurs discovered they could generate and sell to domestic users to run things like light bulbs, electric irons, heaters etc., you get the idea.
So you'd have a steam engine coupled to a dynamo and this machine could generate maybe 10 or 20 kilowatts at say 200 Volts DC (100 in the US) and wires would be strung up around the local community so houses were connected up.
Unfortunately the shortcomings very soon showed up, like the poor sod at the very end if the wire was lucky to get half the voltage that started out.
Back to the drawing board.
No prizes for seeing the obvious, DC was no good and everything had to be changed to run AC so that big transformers could be used to enable long distance transmission of power. ( you lose a lot less of 1A at 20,000 Volts than you do of 100A at 200 V down the same bit of wire).
But you couldn't just send 200V AC becouse everybody already had their bulbs and irons and the like so you needed to send the same in heating power which is Square root 2 x the original, 1.414 x 200 = 280ish volts.
This is RMS volts.
OK, back to amplifiers.
So we all hope everyone uses the same specs so we can compare like for like. Unfortunately this does not happen.
The Gold Standard is RMS Watts continuous, a sine wave, undistorted running continuously into a specified load, usually 8 Ohms.
An amplifier run like this puts a hefty load on it's power supply which will provide a reduced voltage (this is where good regulation comes in).
Under these conditions you can either take the peak signal or the RMS signal and the peak will be twice the RMS.
If a manufacturer want to cheat (and a lot do) he can make his amp look twice as good as the next guys by saying, oh yes this is a thirty watt amp, when really it's only 15 W RMS.
It gets worse.
Imagine an amp with a very poor power supply, which starts out at say 20 volts unloaded but when run with a continuous load drops to 10 volts. A short pulse fed in could put out a 10 volt peak pulse output. into 8 ohms this is 13 Watts peak. Running continuous it drops to 10 V supply which is 5 V peak or 3.1 W peak or 1.5 W RMS.
But hang on we have two channels so that's 26 Watts peak from what is really only a 1.5 Watt amp. This is charmingly called PMPO (peak music power output). The horrid noise boxes accompanying computers are often rated like this. We've all seen them, 150 Watts (pmpo) shouted at you when really you're lucky to get 8 watts RMS.
So It's important to specify all the parameters when quoting a figure. So many on this site forget to do this so we have things quoted like 10 Watts, but that could mean almost anything, is it RMS or peak or what?
Earlier there was a quote that went 1.85A peak so thats 3.7A p to p....?
Thats kinda nonsense really.
Here endeth the lesson as I now have writers cramp.
Regards to all
Henry
I see we have all finally reached an accord, that's nice, the forum works.
A bit more info for Kingfisher.
Way, way back in the mists of time, even long before my time, there was this new thing electricity, which entrepreneurs discovered they could generate and sell to domestic users to run things like light bulbs, electric irons, heaters etc., you get the idea.
So you'd have a steam engine coupled to a dynamo and this machine could generate maybe 10 or 20 kilowatts at say 200 Volts DC (100 in the US) and wires would be strung up around the local community so houses were connected up.
Unfortunately the shortcomings very soon showed up, like the poor sod at the very end if the wire was lucky to get half the voltage that started out.
Back to the drawing board.
No prizes for seeing the obvious, DC was no good and everything had to be changed to run AC so that big transformers could be used to enable long distance transmission of power. ( you lose a lot less of 1A at 20,000 Volts than you do of 100A at 200 V down the same bit of wire).
But you couldn't just send 200V AC becouse everybody already had their bulbs and irons and the like so you needed to send the same in heating power which is Square root 2 x the original, 1.414 x 200 = 280ish volts.
This is RMS volts.
OK, back to amplifiers.
So we all hope everyone uses the same specs so we can compare like for like. Unfortunately this does not happen.
The Gold Standard is RMS Watts continuous, a sine wave, undistorted running continuously into a specified load, usually 8 Ohms.
An amplifier run like this puts a hefty load on it's power supply which will provide a reduced voltage (this is where good regulation comes in).
Under these conditions you can either take the peak signal or the RMS signal and the peak will be twice the RMS.
If a manufacturer want to cheat (and a lot do) he can make his amp look twice as good as the next guys by saying, oh yes this is a thirty watt amp, when really it's only 15 W RMS.
It gets worse.
Imagine an amp with a very poor power supply, which starts out at say 20 volts unloaded but when run with a continuous load drops to 10 volts. A short pulse fed in could put out a 10 volt peak pulse output. into 8 ohms this is 13 Watts peak. Running continuous it drops to 10 V supply which is 5 V peak or 3.1 W peak or 1.5 W RMS.
But hang on we have two channels so that's 26 Watts peak from what is really only a 1.5 Watt amp. This is charmingly called PMPO (peak music power output). The horrid noise boxes accompanying computers are often rated like this. We've all seen them, 150 Watts (pmpo) shouted at you when really you're lucky to get 8 watts RMS.
So It's important to specify all the parameters when quoting a figure. So many on this site forget to do this so we have things quoted like 10 Watts, but that could mean almost anything, is it RMS or peak or what?
Earlier there was a quote that went 1.85A peak so thats 3.7A p to p....?
Thats kinda nonsense really.
Here endeth the lesson as I now have writers cramp.
Regards to all
Henry
well put !
I particularly like the history and why the AC voltage had to have the same heating effect as a DC supply. That is the most important part. 100Vac must have the same heating effect as 100Vdc.
If the AC is sinewave with zero harmonics then we know the peak to peak voltage of the sinewave, just as top explained. Then we can call our voltage 100Vrms 50/60Hz sinewave.
Personally I prefer not to use this term. I prefer Vac and part of the reason for doing that is most of my voltmeters cannot measure Vrms and most of the signals I measure or use, are not a zero distortion sinewave.
Thank you.
Fair point with the Vac, but we're getting into oscilloscope territory rather than meters.
Fair point with the Vac, but we're getting into oscilloscope territory rather than meters.
Thank you toprepairman and Andrew T for going through the calc's. when I originally went through what Andrew was calculating I used a different formula to see if we got the same results and some confusion when I plugged in a bad number (put in double the current which was the nonesense!) In redoing the compliance calc with the correct current value it came out to the estimated wattage that you have.
As most said there is a very heavy price in heat(power) to pay for Single End class A. It will be interesting to see the scope measurements on an 8 Ohm load..if and when the bias can be brought to the 4A range...guess that is the next step for Eric. Anyways it is cold in Canada right now so good time to try!!
As most said there is a very heavy price in heat(power) to pay for Single End class A. It will be interesting to see the scope measurements on an 8 Ohm load..if and when the bias can be brought to the 4A range...guess that is the next step for Eric. Anyways it is cold in Canada right now so good time to try!!
Hi toprepaiman, ac fake power are still strange for some people, the different of int(V*I)dt and int(V)dt*int(I)dt or Pwr(rms) and Vrms*Irms.
3 phase line transmission system is where AC is the winner in efficiency and cost. DC and AC choice is old problem solved when the inventors still alife, they has "little funny cold war" about that, and Nicola Tesla win the AC than Edison with DC. There also old problems like reactive power (fake power measured), and Y and delta load configuration at 3phase.
3 phase line transmission system is where AC is the winner in efficiency and cost. DC and AC choice is old problem solved when the inventors still alife, they has "little funny cold war" about that, and Nicola Tesla win the AC than Edison with DC. There also old problems like reactive power (fake power measured), and Y and delta load configuration at 3phase.
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Hey Arick, I just wanted to do a bit of comparison as to the whole wattage efficiency thing. My tube amp is rated 50W (yes that's RMS into 8 Ohm) using 2 EL-34's in push pull, class AB with an ultralinear configured output transformer. Running full out it consumes about 200W total power.
Does it get Hot? Absolutely
Is it efficient? Not very much
Would I trade it in for a nice little transistorized Class D amp at 1/10th the size and weight with amazing ''efficiency''? Over my dead body!!! Well I am sure you guessed that answer.
Let me know how the ''soft start'' tests go..can't wait to hear when the amp's running again!!
Does it get Hot? Absolutely
Is it efficient? Not very much
Would I trade it in for a nice little transistorized Class D amp at 1/10th the size and weight with amazing ''efficiency''? Over my dead body!!! Well I am sure you guessed that answer.
Let me know how the ''soft start'' tests go..can't wait to hear when the amp's running again!!
Sure about what? I was talking about the total power consumption of the whole amp..yeah when I rebuilt it a couple of year's ago I had to take a lot of measurements...
Yes (the tube amp) it's a mono amp, a bit old and a lot of turret board and point to point. But I guess this is moving off the thread topic... I think Arick is in the process of finishing up the soft start section and doing some additional circuit mods to protect the LMs at power on. From his posting a while back, the Mosfets seem to be fine.
So looking forward to his next post to see how it is running.
So looking forward to his next post to see how it is running.
That is true, it was not considerably less. The valve heaters, power supply series resistors etc eat up a lot of that power even when idling. Cold, on startup obviously even more power required from mains.
Back on that topic it brings up one of the issues Arick was having on the power up: there is a huge amount of inrush on the mains just to get those (big) PS filter caps fully charged.
He has problem with lm117, I don't know what actually his supply is, if it used +/-40 it then 80V in total and if it +/-35 it then 70V. both will kill those lm117. If his supply is 40 they probably killed by power derating. 6x lm117 is only 120Watts.
NB: Hi,Shanx, did your EL-34 shine bright like a bulb?
NB: Hi,Shanx, did your EL-34 shine bright like a bulb?
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Hi Ontoaba, looks like the design specifically calls for HV versions on the LMs. And even then they will instantly breakdown if over the limit..it seems a soft start circuit is ''a must'' to ensure the voltages stabilize properly to avoid killing the LMs.
Thankfully, the only elements of the EL34s that are glowing are the parts that are supposed to (!) BTW if you have any forums that look particularly interesting on valve amps or preamps please let me know about them..there are so many posts!!
Umm.. I don't have it, I have only tube for RF, where tube has high power compared to solid state, hot...😱 I have some friends selling tubes and repair them in Surabaya and now I stay in Kudus (300Km from them). And playing with solidstate. I am now going to emulate 50W SEclassA with 4pair TIP41/41 in classB.🙂
It is off topic😀 Lets wait Eric's for the result.
It is off topic😀 Lets wait Eric's for the result.
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