Guys,
I see number of SE KT88 amplifiers on the market advertising 15W outputs power.
Any ideas how do they do it ? How do they get 15 watts out of single KT88/6550 tube ? I think, they use tube in pentode mode.
I have breadboarded a simple KT88 amp using 2.5k OT and I only get about 6...8 watts before onset of clipping. Supply voltage is 400vdc and I used fixed bias.
Any comments ?
Thanks
Sergey
I see number of SE KT88 amplifiers on the market advertising 15W outputs power.
Any ideas how do they do it ? How do they get 15 watts out of single KT88/6550 tube ? I think, they use tube in pentode mode.
I have breadboarded a simple KT88 amp using 2.5k OT and I only get about 6...8 watts before onset of clipping. Supply voltage is 400vdc and I used fixed bias.
Any comments ?
Thanks
Sergey
SE Amp CAD gives 8.6Wrms / 17.2W peak with a 6550 using your parameters and 80mA bias when driven almost to grid zero. Distorion is 8%
Info.+
Very tough to get KT88 15 watts in triode mode. Must be tetrode operation. Depending on the brand, distortion varies widely.
As Brett mentioned and per your conditions, in tetrode mode, distortion is high. 2.5k OPT is way too low for low distortion operation.
Svetlana, EH, and Sovtek give the lowest distortions, with JJs, MOJOs twice the distortion. In my opinion, Svetlana and EH give the best sonics.
Hope this helps.
Very tough to get KT88 15 watts in triode mode. Must be tetrode operation. Depending on the brand, distortion varies widely.
As Brett mentioned and per your conditions, in tetrode mode, distortion is high. 2.5k OPT is way too low for low distortion operation.
Svetlana, EH, and Sovtek give the lowest distortions, with JJs, MOJOs twice the distortion. In my opinion, Svetlana and EH give the best sonics.
Hope this helps.
Re: Info.+
That was triode. So I think manufacturers are using the 'peak' number to sell to customers. I only spec in RMS, and define clipping as 1%.
Positron said:
That was triode. So I think manufacturers are using the 'peak' number to sell to customers. I only spec in RMS, and define clipping as 1%.
Brett,
What's the difference between RMS and PEAK power ?
And how would you measure PEAK power ?
Thanks
What's the difference between RMS and PEAK power ?
And how would you measure PEAK power ?
Thanks
Thanks.
Thanks Brett. I have seen peak or music, instead of RMS, used before.
It wouldn't surprise me to see 8% with a 2.5k tranny, in triode mode, maybe more or less, depending on the brand tube used. Personally, I have never worked with that low tranny with that tube.
Take care and thanks Brett.
Thanks Brett. I have seen peak or music, instead of RMS, used before.
It wouldn't surprise me to see 8% with a 2.5k tranny, in triode mode, maybe more or less, depending on the brand tube used. Personally, I have never worked with that low tranny with that tube.
Take care and thanks Brett.
That old chestnut...
Hi,
As mentioned in previous threads, there is actually no such thing as "RMS power"; There's "Power". The same stuff that heats up a kettle. There is no need to check whether your kettle is "RMS" 😉
"RMS power" was just a term that equipment manufacturers thought up to differentiate real power from ficticious (peak) power measurements.
I know a little about how they go about calculating "Peak power", but I can't for the life of me see how it could be higher than the real power for class A.
Imaginitive power ratings in class A can only depend on the distortion figure referenced.
With DC coupling it is possible to move into class A2. Just under 40% is possible there, but it is device dependent, and getting good results is a non-trivial task.
Cheers,
Hi,
As mentioned in previous threads, there is actually no such thing as "RMS power"; There's "Power". The same stuff that heats up a kettle. There is no need to check whether your kettle is "RMS" 😉
"RMS power" was just a term that equipment manufacturers thought up to differentiate real power from ficticious (peak) power measurements.
I know a little about how they go about calculating "Peak power", but I can't for the life of me see how it could be higher than the real power for class A.
Imaginitive power ratings in class A can only depend on the distortion figure referenced.
That is for class A1 operation, and is typical of what can be achieved with RC coupling.
With DC coupling it is possible to move into class A2. Just under 40% is possible there, but it is device dependent, and getting good results is a non-trivial task.
Cheers,
Peak power is simply the mathematical power given or drawn at the peak voltage of an AC signal. RMS power is power measured at volts RMS, instead of volts peak. RMS is the useful, or "REAL" voltage and is calculated by multiplying .707 to the peak voltage. Rarely, however, is voltage measured peak, but normally RMS. Power is not by designation to be expressed as "watts RMS," it really means, "watts calculated at volts RMS," since volts are supposed to measure at either RMS or PEAK.
Also, note that DC voltages don't exist in either RMS or PEAK, they are simple volts DC.
The full scope of the matter is somewhat complicated, however, I hope I have cleared the air as to what watts RMS and watts PEAK really mean.
Also, note that DC voltages don't exist in either RMS or PEAK, they are simple volts DC.
The full scope of the matter is somewhat complicated, however, I hope I have cleared the air as to what watts RMS and watts PEAK really mean.
Original-flavor 6L6, as Pentode, was rated about 10 watts output in SE.
I have on my bench a 1938 PA amplifier that runs the 6L6 a little past the design-center specs and delivers 9 watts despite transformer losses (which are substantial in a SE transformer with good bass response).
FWIW: original 6L6 working somewhat under-rating as SE-Triode claimed something like 1.4W. I bet it could do more, but not a huge amount more inside the original 360V plate rating. (6L6GC with higher plate voltage rating could do a lot better, if you can wind a primary to high impedance.)
As a 6550 is roughly twice the size of an original 6L6, I would expect well over 10 watts if you got it powered and loaded right. For gitar-amp duty, where tube-life and low-THD are not the main selling factors, 15 watts should be easy even with an inexpensive (lossy) output transformer.
As Triode, I'd think 15W from 6550 is awful high. I bet I could demo it with a great transformer and either high THD (15%, tolerable on gitar) or heavy feedback. But the poor tube would go soft and die in hours. (Some cheap 6550 might arc and explode at turn-on at the voltage and current needed to hit 15W SET, and the screen grid would not last long.)
WTH: 6L6GC is so cheap, you can afford two, and easily beat 15W SE Pentode loafing. While the 6550 is a big hunk of power in one bottle, on today's market the 6L6GC is a better watt/buck buy and you have a much wider selection. And 6L6GC are in-stock locally on Saturday when your Friday night gig eats your tubes.
> using 2.5k OT
That is sure too low for 6L6 Triode; probably a bit low for 6550 working 400V because the plate dissipation limits the idle current. Try 5K load. If you don't mind maybe-killing tubes, take the plate voltage higher, though you may already be at the screen-grid (or Triode plate) voltage rating (too lazy to look it up for you).
Don't fret too much about the actual power number. If 10 watts is not enough, then you probably want 40 to 100 watts to make you say WOW!. From 10 to 15 watts is just "hmmm...". Changes in how it clips when the power is goosed will affect the "sound" more than any little 50% change in power.
I have on my bench a 1938 PA amplifier that runs the 6L6 a little past the design-center specs and delivers 9 watts despite transformer losses (which are substantial in a SE transformer with good bass response).
FWIW: original 6L6 working somewhat under-rating as SE-Triode claimed something like 1.4W. I bet it could do more, but not a huge amount more inside the original 360V plate rating. (6L6GC with higher plate voltage rating could do a lot better, if you can wind a primary to high impedance.)
As a 6550 is roughly twice the size of an original 6L6, I would expect well over 10 watts if you got it powered and loaded right. For gitar-amp duty, where tube-life and low-THD are not the main selling factors, 15 watts should be easy even with an inexpensive (lossy) output transformer.
As Triode, I'd think 15W from 6550 is awful high. I bet I could demo it with a great transformer and either high THD (15%, tolerable on gitar) or heavy feedback. But the poor tube would go soft and die in hours. (Some cheap 6550 might arc and explode at turn-on at the voltage and current needed to hit 15W SET, and the screen grid would not last long.)
WTH: 6L6GC is so cheap, you can afford two, and easily beat 15W SE Pentode loafing. While the 6550 is a big hunk of power in one bottle, on today's market the 6L6GC is a better watt/buck buy and you have a much wider selection. And 6L6GC are in-stock locally on Saturday when your Friday night gig eats your tubes.
> using 2.5k OT
That is sure too low for 6L6 Triode; probably a bit low for 6550 working 400V because the plate dissipation limits the idle current. Try 5K load. If you don't mind maybe-killing tubes, take the plate voltage higher, though you may already be at the screen-grid (or Triode plate) voltage rating (too lazy to look it up for you).
Don't fret too much about the actual power number. If 10 watts is not enough, then you probably want 40 to 100 watts to make you say WOW!. From 10 to 15 watts is just "hmmm...". Changes in how it clips when the power is goosed will affect the "sound" more than any little 50% change in power.
Some day I'm going to have to take a 6L6 in class A2 and get 30W SE out of it. 😉
Clearly, only intermittent use
Tim
Clearly, only intermittent use
Tim
Well, I do not build tube amps.
My father did however.
He claimed his one-channel 6L6G push-pull Class AB produced 24Watts and when I was much younger, I used it as the amp for our drive-in show. Knowing my father it was built to mil-specs. So it could take some beating....
It had a phono in with a RIAA correction based on the 707opamp, and three din-inputs, switchable with neon indicators, bass and treble control. Tube rectifier and a soft-start. Even two meters, but I do not know which parameter you could read from them. I'll ask him. 😉
But the amp is still working occasionaly and I'm fourty now ... 🙂
Jos
My father did however.
He claimed his one-channel 6L6G push-pull Class AB produced 24Watts and when I was much younger, I used it as the amp for our drive-in show. Knowing my father it was built to mil-specs. So it could take some beating....
It had a phono in with a RIAA correction based on the 707opamp, and three din-inputs, switchable with neon indicators, bass and treble control. Tube rectifier and a soft-start. Even two meters, but I do not know which parameter you could read from them. I'll ask him. 😉
But the amp is still working occasionaly and I'm fourty now ... 🙂
Jos
Hi,
Most of the powers we've been passing round are for triode mode. I have to admit that I've forgotten how to calculate the max power in tetrode/pentode mode😱 I'm sure though, that it must have been AB tetrode/pentode.
Cheers,
Most of the powers we've been passing round are for triode mode. I have to admit that I've forgotten how to calculate the max power in tetrode/pentode mode😱 I'm sure though, that it must have been AB tetrode/pentode.
Cheers,
Hi,
Want a X-mass tree?
Run the heaters at 12V too...not that it's going to live for long, but it'll be fun.
Cheers,😉
Want a X-mass tree?
Run the heaters at 12V too...not that it's going to live for long, but it'll be fun.
Cheers,😉
Hey, 30W output, 33% efficiency (typical class A pentode), that's 90W supply so plate dissipation is only 60W, twice the published rating. Ran for a minute tops, the plate shouldn't get too hot. 😎
If screen is ran relatively low (which will also keep it from toaster-oven-ing) you might even be able to run zero bias, making for an easier load for the driver. 🙂
Tim
If screen is ran relatively low (which will also keep it from toaster-oven-ing) you might even be able to run zero bias, making for an easier load for the driver. 🙂
Tim
Hi,
Look at it this way, if triggered on July 11th the amp would display all the national colours and auto-finish with Jimmy Hendricks's Star Spangled Banner...so?
What's the problem???
Bye,😉
Look at it this way, if triggered on July 11th the amp would display all the national colours and auto-finish with Jimmy Hendricks's Star Spangled Banner...so?
What's the problem???
Bye,😉
KT88 SE Circuits
Hi. Interesting thread for me as I have a pair of 88s and was looking to build a single ended stereo amp of about 10W per channel.
I'm not too worried about distortion at higher powers but a reasonably clean 5 to 6 Watts would be great.
I had considered the Pye Mozart HF20 circuit (EL34s and cathode F/B because the quoted performance figures were impressive. Lack of finances and rarity of output transformers with the cathode bias primary winding has probably ruled that option out.
I'm currently running a 3.5W SE power amp using ECC83/SV83 through 2 pairs of stacked Quad 57 electrostatics and the sound it exceptionally good. A wee bit more power would be beneficial.
Does anyone have direct experience of designs using KT88s in SE mode, either tetrode or triode operation? Can you recommend one? I have built my usual aluminium and wood enclosure (this amp will be my 8th scratch built project)and need to settle on a design before construction continues.
I'd happily settle for 3W SE in triode mode as that design topology differs from pentode SE that I am currently using/
Cheers
Best
Andy
Hi. Interesting thread for me as I have a pair of 88s and was looking to build a single ended stereo amp of about 10W per channel.
I'm not too worried about distortion at higher powers but a reasonably clean 5 to 6 Watts would be great.
I had considered the Pye Mozart HF20 circuit (EL34s and cathode F/B because the quoted performance figures were impressive. Lack of finances and rarity of output transformers with the cathode bias primary winding has probably ruled that option out.
I'm currently running a 3.5W SE power amp using ECC83/SV83 through 2 pairs of stacked Quad 57 electrostatics and the sound it exceptionally good. A wee bit more power would be beneficial.
Does anyone have direct experience of designs using KT88s in SE mode, either tetrode or triode operation? Can you recommend one? I have built my usual aluminium and wood enclosure (this amp will be my 8th scratch built project)and need to settle on a design before construction continues.
I'd happily settle for 3W SE in triode mode as that design topology differs from pentode SE that I am currently using/
Cheers
Best
Andy