By that, most commercial (and most DIY?) KT88 based tube amps usually have 2 tubes per channel (or more). Is there something that makes using a single tube per channel undesirable?
I know from a marketing point of view, it is easier to sell a ~75 watt per channel amp (which two tubes per channel give you), but is there something about the tube, design that makes it idea to use with a minimum of 2 tubes per channel? This is opposed to other tubes that are mostly or always used as singles per channel.
Looking online I think there are some random single KT88/channel amps, but seems to be rare and maybe DIY only.
I know from a marketing point of view, it is easier to sell a ~75 watt per channel amp (which two tubes per channel give you), but is there something about the tube, design that makes it idea to use with a minimum of 2 tubes per channel? This is opposed to other tubes that are mostly or always used as singles per channel.
Looking online I think there are some random single KT88/channel amps, but seems to be rare and maybe DIY only.
Single-ended power amps make sense only for very small power. So a single 6V6 (4W) may make sense. A single-ended 6550/KT88 (13W) is heavier and more expensive and higher THD than a push-pull 6V6 amp.
Many tube amps, maybe most, are push-pull designs requiring at least 2 tubes per channel. One for each half of the waveform. The KT-88 being a fairly high power tube is a popular choice.
You can use just one in a single ended tube amp, these tend to be low power and have pretty specific design goals. A KT-88 would work fine but but is probably not the most obvious choice...John
You can use just one in a single ended tube amp, these tend to be low power and have pretty specific design goals. A KT-88 would work fine but but is probably not the most obvious choice...John
Thanks!
So a case of 'just because you can does not mean you should' - no technical limitation, just not a good solution.
So a case of 'just because you can does not mean you should' - no technical limitation, just not a good solution.
Parallel tubes in a properly designed, and properly implemented amplifier can be a good thing.
Either Bad design, Or Bad implementation, or Both = Bad.
All designs have made some kind of tradeoff or other.
"All Generalizations Have Exceptions"
Either Bad design, Or Bad implementation, or Both = Bad.
All designs have made some kind of tradeoff or other.
"All Generalizations Have Exceptions"
He's asking about "commercial". While there are parallel commercial amps, he also mentions "75W/channel", which is clearly more than two SE KT88.
I read the question as about the commercial advantage of Push-Pull over any other connection. Since 1939, past around 10W output, push-pull is cheaper than SE. At 17W PP can be about half the price (my SE 6550 17W was sure more expensive than an over-volted P-P DeLuxe of 15W-20W).
… and multiple output tubes are prettier than singles. Like now so many modern zippy looking automobiles have fake 'extra exhaust pipes'. You can always tell 'cuz the real pipes are black on the inside, and the fakes are often still silvery.
For many, looks are important.
For many of us, 10 watts of really good SE, combined with excellent mid-to-high efficiency speakers and as much attention given to the listening space as to all the fancy electronics, well … that's the best balance.
So sez an OLD goat.
⋅-=≡ GoatGuy ✓ ≡=-⋅
For many, looks are important.
For many of us, 10 watts of really good SE, combined with excellent mid-to-high efficiency speakers and as much attention given to the listening space as to all the fancy electronics, well … that's the best balance.
So sez an OLD goat.
⋅-=≡ GoatGuy ✓ ≡=-⋅
Do you want efficiency?
Then purchase a Class D solid state amplifier.
I like single ended tube amps.
I like push pull tube amps.
I have never purchased a class D amplifier.
Just my opinions, and just my practice.
Then purchase a Class D solid state amplifier.
I like single ended tube amps.
I like push pull tube amps.
I have never purchased a class D amplifier.
Just my opinions, and just my practice.
Actually, a great solution if you want SET sound with some extra power (vs. something like EL34 or 6L6GC). Plenty of people build the Tubelab Simple SE and stick KT-88s in it, for example. A perfectly reasonable thing to do.
There are a lot of folks out there who much prefer the sound of single-ended amps vs. push-pull - regardless of what tubes they are running.
The efficiency argument makes me chuckle. Yes, my 25 WPC push-pull amp is twice as "efficient", technically, as my 7 WPC SET amp, however, the P-P amp is running 4 power tubes at 24 watts dissipation and pulling a around 200 watts from the wall, whereas my SET is running 2 power tubes at about 22 watts dissipation and pulling well under 100 watts from the wall. Since I never use much more than 5 or 6 watts of amplifier power, the SET is by far the better choice, and it sounds better.
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Often one characteristic difference between Single Ended and Push Pull amplifiers is that, an SE amp has dominant 2nd harmonic distortion, and a PP amp has dominant 3rd harmonic distortion.
A way to get adjustable dominant 2nd harmonic distortion from an otherwise good push pull amplifier, is to:
Remove any global negative feedback around the stage that is modified below:
Now, you can Un-balance either the phase splitter gains, or the driver gains.
Using a perfectly balanced cathode coupled phase splitter (one that has equal plate load resistors, and that has a true current source in the cathode circuit), the adjustment is to parallel one of the plate load resistors with a resistance that gives the amplifier the desired amount of dominant 2nd harmonic distortion.
Of course that is why I suggested to eliminate the global negative feedback around that stage, it would have corrected and reduced the 2nd harmonic distortion.
So lets compare an SE amplifier that does not have global negative feedback, with a PP amplifier that does not have global negative feedback:
At that point, two other major differences between the SE and PP amp is the following:
1. The SE amplifier has Un-equal damping factors of the positive going signal, versus the negative going signal.
But the PP amplifier has Equal damping factors of both the positive going signal, and the negative going signal.
2. The output transformers are different.
Primary Inductance that the tubes have to drive
Hysteresis curves that do Not cross zero, versus hysteresis curves that Do cross zero (single ended, versus push pull, respectively).
SE, with an Air Gap to reduce the effect of DC current times turns (amp x turns product).
PP, with no Air Gap, and either perfectly balanced DC currents from the push and pull plates, or Not perfectly balanced DC currents from the push and pull plates.
. . . And other factors, of the particular transformers; factors which most all output transformers have:
Leakage Inductance
Distributed Capacitance.
DCR of primary, DCR of secondary.
Laminations, amount, etc.
Insertion Loss.
(to name a few factors).
Note:
In order to run many kinds of amplifiers with no global negative feedback, that usually changes other factors of the amplifier, including output tubes and tube operating modes.
Triode output tubes; Triode wired Pentode; Triode wired Beam Power; Triode wired Beam Tetrode;
Ultra Linear Pentode; Ultra Linear Beam Power; and Ultra linear Beam Tetrode.
(Some use the name Beam Power, and some use the name Beam Tetrode. That is 2 names for the same tube type).
A way to get adjustable dominant 2nd harmonic distortion from an otherwise good push pull amplifier, is to:
Remove any global negative feedback around the stage that is modified below:
Now, you can Un-balance either the phase splitter gains, or the driver gains.
Using a perfectly balanced cathode coupled phase splitter (one that has equal plate load resistors, and that has a true current source in the cathode circuit), the adjustment is to parallel one of the plate load resistors with a resistance that gives the amplifier the desired amount of dominant 2nd harmonic distortion.
Of course that is why I suggested to eliminate the global negative feedback around that stage, it would have corrected and reduced the 2nd harmonic distortion.
So lets compare an SE amplifier that does not have global negative feedback, with a PP amplifier that does not have global negative feedback:
At that point, two other major differences between the SE and PP amp is the following:
1. The SE amplifier has Un-equal damping factors of the positive going signal, versus the negative going signal.
But the PP amplifier has Equal damping factors of both the positive going signal, and the negative going signal.
2. The output transformers are different.
Primary Inductance that the tubes have to drive
Hysteresis curves that do Not cross zero, versus hysteresis curves that Do cross zero (single ended, versus push pull, respectively).
SE, with an Air Gap to reduce the effect of DC current times turns (amp x turns product).
PP, with no Air Gap, and either perfectly balanced DC currents from the push and pull plates, or Not perfectly balanced DC currents from the push and pull plates.
. . . And other factors, of the particular transformers; factors which most all output transformers have:
Leakage Inductance
Distributed Capacitance.
DCR of primary, DCR of secondary.
Laminations, amount, etc.
Insertion Loss.
(to name a few factors).
Note:
In order to run many kinds of amplifiers with no global negative feedback, that usually changes other factors of the amplifier, including output tubes and tube operating modes.
Triode output tubes; Triode wired Pentode; Triode wired Beam Power; Triode wired Beam Tetrode;
Ultra Linear Pentode; Ultra Linear Beam Power; and Ultra linear Beam Tetrode.
(Some use the name Beam Power, and some use the name Beam Tetrode. That is 2 names for the same tube type).
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I have always thought that the KT88 would make a great substitution for the F2a in building a clone of the famous Shindo Cortese single ended amplifier. If I ever get the time...
There is nothing to chuckle about. It's just engineering. A 6 watt PP would be a better choice on efficiency grounds, subjective elements aside.
A 10 Watt class D amplifier should use less than 15 Watts from the power mains.
A single KT88 filament uses 10.08 watts, and we did not even power the B+ yet.
I like tube amplifiers even if they are not as efficient as Class D, whether the tubes are run in SE or PP.
A single KT88 filament uses 10.08 watts, and we did not even power the B+ yet.
I like tube amplifiers even if they are not as efficient as Class D, whether the tubes are run in SE or PP.
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There is room in my house for any/all of the above. I prefer my tube amps so far, but I must say my TPA3118D2 "Wiener" is a great sounding amp. The efficiency is great for the summer when it is 42 Celsius outside and 32 Celsius inside my house. The fact that an amp smaller than a Kleenex box with a 40VA 24V transformer can easily provide more audio watts than my huge, hot SET amp (which cost me 8X as much to build) isn't lost on me. But I still prefer the sound of the tube amp.
I'll be starting a JLH 1969 Class A amp build soon. Who knows, maybe I'll like the sound of it better than my tube amps. I'm not married to any amplifier - I can build as many as I want and I plan on doing so.
I'll be starting a JLH 1969 Class A amp build soon. Who knows, maybe I'll like the sound of it better than my tube amps. I'm not married to any amplifier - I can build as many as I want and I plan on doing so.
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As I said in an earlier post, no class D amplifiers for me.
I like to use a portable battery powered AM radio throughout the house.
Some stations I listen to are weak; but even the strong stations suffer:
All the devices I have in the house meet EMI regulations.
In the interest of power efficiency, all the "Wall Wart" transformer/rectifier/cap filter power supplies, were replaced by switcher supply wall warts.
The same thing goes for many products that have internal power supplies.
The old transformers and linear supplies are becoming a thing of the past: Expensive, heavy to ship, etc.
Switcher supplies:
Microwave display and clock ; stove digital display and clock; digital clock radio;
CD and DVD players; Digital TV; cell phone charger, PC; LED light bulbs; Landline RF phone and message recorder; and more devices that I can not even think of now.
EMI means Electro Magnetic Interference.
Devices all pass EMI regulations.
But, they all interfere to one degree or another.
EMC means Electro Magnetic Compatibility.
But a battery powered AM radio is Not compatible with any of the above devices.
I am not adding another device that has a switcher, computer chip, digital circuit, or other interfering source, such as a Class D amplifier to my house.
I like to use a portable battery powered AM radio throughout the house.
Some stations I listen to are weak; but even the strong stations suffer:
All the devices I have in the house meet EMI regulations.
In the interest of power efficiency, all the "Wall Wart" transformer/rectifier/cap filter power supplies, were replaced by switcher supply wall warts.
The same thing goes for many products that have internal power supplies.
The old transformers and linear supplies are becoming a thing of the past: Expensive, heavy to ship, etc.
Switcher supplies:
Microwave display and clock ; stove digital display and clock; digital clock radio;
CD and DVD players; Digital TV; cell phone charger, PC; LED light bulbs; Landline RF phone and message recorder; and more devices that I can not even think of now.
EMI means Electro Magnetic Interference.
Devices all pass EMI regulations.
But, they all interfere to one degree or another.
EMC means Electro Magnetic Compatibility.
But a battery powered AM radio is Not compatible with any of the above devices.
I am not adding another device that has a switcher, computer chip, digital circuit, or other interfering source, such as a Class D amplifier to my house.
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