tube watts louder than transistor watts ???

[Captain Kilowatt]

You missed the pep power with modulation. The 270 watts of carrier you are talking about is just the unmodulated carrier. Throw some modulation into the mix and watch your tubes start to take on an unhealthy glow.

I think if you have 3000vdc @ 150ma for 450 watts of input, even at 60% efficiency and a 270 watt carrier, that leaves 180 watts for the plate to dissipate ...... or did I miss something very important

 

[W5LZ]

That 60% efficiency is the whole amplifier. The plate still has to dissipate all that goes through that amplifier. The 'efficiency' doesn't refer to the plate's ability to dissipate power.
- 'Doc

(and just for grins, I think that 60% is a bit optimistic.)

 

[GnG8d]

You missed the pep power with modulation. The 270 watts of carrier you are talking about is just the unmodulated carrier. Throw some modulation into the mix and watch your tubes start to take on an unhealthy glow.

I just followed the example using carrier power. But 270 watts modulated to 1080 watts doesn't seem out of the question to me, given a duty cycle of 15-25% for the human voice.

 

[GnG8d]

That 60% efficiency is the whole amplifier. The plate still has to dissipate all that goes through that amplifier. The 'efficiency' doesn't refer to the plate's ability to dissipate power.
- 'Doc

(and just for grins, I think that 60% is a bit optimistic.)

I'm not following. You can look at efficiency at the vac line in, or the efficiency of the vdc present at the tube plate. Ameritron claims 70% efficiency and I have to assume that's at the tube plate, because the vac line in has a lot of lost power like meter lights, cooling fan, heat from caps/resistors, cathode/heater etc.. So you see, the plate does not have to dissipate everything that goes through the amp from the vac line in, and actually doesn't have to dissipate everything presented to the plate directly.

Of the 450 watts used in the example, some will be dissipated by the plate, tune/load cap, feedline, antenna etc., and not all of it is dissipated at the plate.

.......... assuming that I'm not completely out to lunch

 

[Captain Kilowatt]

I just followed the example using carrier power. But 270 watts modulated to 1080 watts doesn't seem out of the question to me, given a duty cycle of 15-25% for the human voice.

Try it out and see for yourself. AM operation is hard on tubes and power supply components. Hams have know that since they started operating AM. The components do not get much of a rest between voice peaks because they are still generating a carrier. It's like trying to empty the sink with both taps turned on full blast.

 

[GnG8d]

Try it out and see for yourself.

I seriously doubt I buy a single 3-500z amplifier just to see if it'll do 1kw reliably on AM

 

[Captain Kilowatt]

I seriously doubt I buy a single 3-500z amplifier just to see if it'll do 1kw reliably on AM

No? Why not? Anyway you know what I meant. It's applicable to ANY tube amp.

 

[Shockwave]

For AM use with this amplifier, you can only run this amplifier to about 150 watts of carrier and talk for short periods of time without overdissapating the tube's plate.
Why: 3000 volts times .150 amp = 450 watts DC 'carrier' power. The tube's plate dissapation is not rated for much more than this.
When the modulated drive signal increases with speech, the average tube dissapation goes up greatly and begins to 'average shift' to higher plate temperatures as seen by the plate continuing to get brighter and brighter with key down time and no chance to cool.
This means you get 150 watts x 4 = 600 watts peak envolope power at the most, safely, using this amplifier in the AM mode, not the 1kw it is rated for in SSB.
The other part of all this is total conversion efficiency.
At 600 watts 'peak' output and assming 50% efficiency, the total 'peak power' DC input would be close to 1200 watts DC.
On SSB, at 1kw output, the DC power input is about 2000 watts on speech peaks.
To further back this up; at 240 volts ac line input, the line is fused at 10 amps. 240vac x 10 amps is 2400 watts or at 120 vac the fuseing is at 20 amps. Both are a 2400 watt rateing so there is some capacity to spare without blowing fuses on speech peaks at full drive limits.

I'm afraid your calculations would only be close if the amp was running around 0% efficiency. At 3000 volts and 150 ma, the tube could only be dissipating 450 watts if there was no output and all power was converted into heating the anode. With 450 watts DC input and 150 watts carrier you have about 300 watts wasted as dissipation under this condition and the average dissipation does not increase when modulated to 100%. The efficiency seems a little low here but that's because a chunk of the 150 ma is your DC bias before any RF is amplified.

AM doesn't draw anymore modulated current then SSB for the same PEP output. In fact if you look at the 150 ma carrier current and modulate it to 100%, the average input current remains steady. That's because the modulated current doubles on positive peaks and goes to zero on negative peaks. That means average current and dissipation does not change. AM is harder on the amp because the current never gets to drop to zero between words as it does on SSB. Not because higher current is consumed but because the duty cycle required for the AM carrier is higher then SSB without the constant carrier.

 

[Shockwave]

To answer the original question, loudness is determined on AM entirely by the difference between the carrier power and the peak modulated power. The larger the difference, the louder the audio. Too much change and you'll be distorted. It has nothing to do with the differences between tubes and transistors.

 

[GnG8d]

Anyway you know what I meant.

yup, I do

 

[Shadetree Mechanic]

Old thread bump. (It's what I do best)

Is it possible that tube amplifiers have better sounding distortion so they can appear to be louder with distortion while sounding good?

 

[Shockwave]

Old thread bump. (It's what I do best)

Is it possible that tube amplifiers have better sounding distortion so they can appear to be louder with distortion while sounding good?

If we are talking about an audio amplifier, I would say yes, it is possible. The preferred distortion of a tube AF amp is not as harsh as a solid state amp when overdriven into distortion.

However, in this case I think we are talking about a linear RF amplifier. You can have a tube modulator stage and feed slightly distorted audio into a tube RF amp and still make it sound more distorted, if that RF amp is clipping all the positive peaks and running the carrier into cutoff.

If you want to "sound" louder, add a compressor and if it's on AM, a negative peak limiter too. You might even be surprised by the results of just flipping the polarity on the two mic wires, if your voice is asymmetrical...

 

[Captain Kilowatt]

Old thread bump. (It's what I do best)

 

[Dmans]

The preferred distortion of a tube AF amp is not as harsh as a solid state amp when overdriven into distortion.

I agree with Shockwave's analysis.
I can attest to the fact that distortion in a tube AF amplifier (my example; a Fender 40 watt Tube Guitar amplifier) is not as harsh as distortion in a transistor amplifier (my example; a Peavey 75 watt Transistor Guitar Amplifier). Recorded demos confirm this with both amplifiers being ran "straight thru" with no effects in-line. The ears heard it immediately.
Therefore the Peavey was sold and I never looked back.

(Talk about de-railing a "Mummy" thread..............)

73
David

 

[Shadetree Mechanic]

If we are talking about an audio amplifier, I would say yes, it is possible. The preferred distortion of a tube AF amp is not as harsh as a solid state amp when overdriven into distortion.

However, in this case I think we are talking about a linear RF amplifier. You can have a tube modulator stage and feed slightly distorted audio into a tube RF amp and still make it sound more distorted, if that RF amp is clipping all the positive peaks and running the carrier into cutoff.

If you want to "sound" louder, add a compressor and if it's on AM, a negative peak limiter too. You might even be surprised by the results of just flipping the polarity on the two mic wires, if your voice is asymmetrical...

Yes, RF amp is what I meant. So boxcars on the scope sound the same with tubes or transistors. But there is a point where the scope starts to look bad but it still sounds good, would tubes allow more leeway at that point on the scope or is it still the same as transistors? I think tubes might be more forgiving but the amplifiers that I have to compare are on different radios because the drive levels are different so I am not sure.