1000w class A

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gswan said:
Most radio transmitter amplifiers are class C. That's how you get the high power, it's tuned to a very narrow band to be fed into an antenna.
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OK. Hard to find info, but looks like the Doherty amp of 1936 was maybe the first to incorporate class C into a combo system for AM use, with class C amps by themselves described as "do not maintain suitable fidelity for AM signals (but work fine for constant-carrier applications like FM
and on-off keying like morse code". (https://www.researchgate.net/publication/259583529_The_Basics_of_the_Doherty_Amplifier)

Possibly I'm misled by a lack of info.

"introduction date of amplifier classes" is a fruitless search.

RCA MI-12246 is a class B 250W audio amp from the 1940's, much heavier than I ever want to deal with, never mind the B+. There's a similar Altec, not certain of it's class, and an STC that's AB1. All enormous.


Tangent, this is a fun deep dive on amp history, in 4 parts:

http://lilienthalengineering.com/100-amplifiers-chapter-1/100-power-amplifiers-to-lift-your-hat
 
gswan said:
Most radio transmitter amplifiers are class C. That's how you get the high power, it's tuned to a very narrow band to be fed into an antenna.
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True, the RF amp sections can all be class C, but for AM an audio amplifier is required to modulate the plate voltage at some point. That audio amplifier must be at least 1/2 the power of the stage it is modulating, and will be class A or class B.
 
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With AM transmitters, the information is in the change of the amplitude of the HF signal. Until the advent of transmitters based on switching technology (class D etc.), there were two versions of AM transmitters, depending on where the modulation was performed. If AM modulation is performed at a low HF signal level, and the modulated signal is then amplified, that output amplifier must be linear, and cannot operate in class C.
If modulation is performed at the output stage, this stage can operate in class C, provided that the modulator amplifier must be linear. It should not be forgotten that only the modulation amplifier should have IIRC a power of approximately 50% of the output power, so for an output power of eg 1kW, a linear power amplifier of 500W should be used for modulation. This modulator amplifier actually modulates the DC power supply for the output stage. When electronic tubes were used for this job, often the same type of tube was used for the output stage and for the modulator, so in the datasheets you will find characteristics for both C and B or AB class operation.

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With FM transmitters, the information is in the frequency change, so class C output amplifiers can be used without any problems. Amplifiers in this class have a constant value of the amplitude of the HF signal output, often tightly limited.
 
I have a valve amp design handbook from years ago, might have been GEC? It had varying outputs from a few watts to 1200W!! That one I remember had V1505 tubes? Can't remember the plate voltage, but it was kVs!!! - I thought, "I'm pretty sure i'll NEVER build THAT ONE!!"

Let me see if I can find the book!!
 
oooh ....just looked at the V1505 on tubedata.org......3kV anode 345mm tall and 90mm dia. (That's about 14" tall by 3&1/2" in old money)!!!!
Do you want the book uploading if I find it??
 

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A bit off-topic, but last year I helped pull out an old tube-type 5KW FM transmitter and installed a new solid-state replacement. The savings in power was immediately noticeable in a couple of ways...The reduced power consumption of the transmitter itself and the reduced heat levels meant that the cooling needs were much reduced.
 
The easiest way to deliver 1000W to a load using a Class A amp, is to daisy chain a 1/2W Class A amp with a 999.5W class D amp [/bad_joke]
 
moamps said:
With AM transmitters, the information is in the change of the amplitude of the HF signal. Until the advent of transmitters based on switching technology (class D etc.), there were two versions of AM transmitters, depending on where the modulation was performed. If AM modulation is performed at a low HF signal level, and the modulated signal is then amplified, that output amplifier must be linear, and cannot operate in class C.
If modulation is performed at the output stage, this stage can operate in class C, provided that the modulator amplifier must be linear. It should not be forgotten that only the modulation amplifier should have IIRC a power of approximately 50% of the output power, so for an output power of eg 1kW, a linear power amplifier of 500W should be used for modulation. This modulator amplifier actually modulates the DC power supply for the output stage. When electronic tubes were used for this job, often the same type of tube was used for the output stage and for the modulator, so in the datasheets you will find characteristics for both C and B or AB class operation.

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With FM transmitters, the information is in the frequency change, so class C output amplifiers can be used without any problems. Amplifiers in this class have a constant value of the amplitude of the HF signal output, often tightly limited.
Click to expand...

The RF/MW world is a whole different beast, there are a lot more classes than audio, for example, Class C, E, J, F. And among them you have sub categories, like Continuous Class F, Class F Inverted, Continuous Class J, etc.... And then, you have the hybrid amplifiers such as Doherty and Chireix. If you really love amplifiers, the RF world has much more possibilities than audio.

Audio power amps nowadays are basically a "as good as it gets" kind of thing, there is always room for improvement, but efficiency of today's Class D amps is already near to the max, and distortion levels continue to diminish, and size shrinks. As for class B/AB amps, distortion is so low, that it is almost unmeasurable unless you have thousands of dollars worth of equipment, we are at a point of splitting hairs.

However, in the RF/MW world, the challenge is to design a power amp with high efficiency, working at extremely high frequencies with ridiculously insane bandwidths like 1GHz, thats the kind of stuff that grants you patents and IEEE fellowships.
 
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The Atma-Sphere front end is a cascode for high gain, and a resistor plate load.. My circuit is not cascode, but uses a triode as active load instead of a resistor, in the form of a differential SSRP. Additionally, the cathode followers have the cathode resistor replaced with a triode as a current source, similar to a White cathode follower. All power triodes have cathode degeneration resistors added, about 7 ohms. All front end tubes 5687. In more recent times I would use ECC99 in some of the locations, but they did not exist when I built mine.

I don't have a schematic handy, but can probably dig one up in the coming months... if you can be patient. The front is sensitive to adjustments, and several 10 turn pots are needed to properly balance the multiple elements of the differential circuit. If still of interest, send me an email and when I dig it up, I'll share it with you
<[email protected]>
Jennifer
 
I'd only really started this thread as a bit of a joke ,
But theres some interesting tube designs have come up .
The Circlotron concept I did hear of before alright but I never knew it was used for audio . Futtermann amplifier rings a bell , maybe its a reference in RDH4 or Wireless World not sure.
The Atma M60 ranges between 45 and 80 watts per channel depending on load ,4-16 ohms
300 watt power consumption . The manual makes it look like its available in kit form but the makers site doesnt mention it .
The hardwire layout, low component count and nothing special in terms of mains transformers makes a DIY attempt very possible , I'd settle for 12watts class A with 75w consumption ,
I hadnt knoticed the ECC99 nor the 5687 , they leave the 12BH7 looking like a prawn in a lobster tank .
 

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