"Pill" questions...

[BOOTY MONSTER]

That was going to be my next question, if you under drive the amp (at or below the rated input of the transistors)...other than a loss of "achievable" power, would a class C amp still splatter (given a clean input)?

it wouldnt be a splatter box but im suprised that freecell didnt point out that class c amps are not even designed for am operation let alone ssb . heres a link thats not extremely tehcnical that tells the proper use for different amp bias classes . http://www.smeter.net/amplifiers/classes.php .

 

[freecell]

like i haven't pointed that out enough times in the past. here it is one more time. class c amplifiers were and are designed for FM, CW, FSK & PM applications, not for AM/SSB. if you bother to study the differences between those modes you'll understand what distinguishes AM/SSB from the rest of them.

5W into a 2290 = 80+W out. 2sc2290.pdf

 

[steved]

Then a class A, AB, or B is what I'm looking for! That was simple enough...

 

[freecell]

you want an AB1 amplifier with the ability to migrate to AB2 with increased drive.

 

[glenn spruille]

So...

A 4-pill box with 1446 transistors should be driven at 28 watts (4 units at 7 input watts)? I assume that is an RMS input?

Steve so 28 is pep correct?

 

[Shockwave]

you want an AB1 amplifier with the ability to migrate to AB2 with increased drive.

Since the discussion relates to transistors, neither class AB1 or AB2 are a possibility without having a grid element inside a tube.

 

[unit_399]

Since the discussion relates to transistors, neither class AB1 or AB2 are a possibility without having a grid element inside a tube.

Absolutely correct. Class AB for solid state amps.

- 399

BTW ... Even though he could be a first class PITA, I miss FREECELL's input here.

 

[Shadetree Mechanic]

your more right then wrong in your way of thinking there Steve :glare: they are what they are , especially the 2 driving 4 :thumbdown: Do they work ? Yes , are they clean ? No , are they over kill ? Yes , again , with what you already learned , what might be the DK and pep from any given radio into a 2 x 4 ? I've seen many an X-force type amp in for repair with those configurations :thumbdown: 2 x 2290s driving 4 x 2879s , How in the hell could you safely drive something like that cleanly or safely enough to not over drive it ? I read somewhere , that anything under a 3/4 watt DK from radio in AM and then the audio from the radio would then suffer , (not saying it wouldn't work) just that the audio would suffer. The old amp section of this Forum (that they decided to leave out) used to have some pretty good threads on this issue and explained it fairly well.

The old amp section that they left out? I wonder if we can get it on the way back machine?

 

[Shockwave]

Steve so 28 is pep correct?

Here is a better question. In a push-pull, 2 transistor RF amplifier being driven with 4 watts, does each transistor see 2 watts of drive or does each transistor alternately get the full 4 watts of drive, one at a time? They are driven through a center tapped, broadband transformer, not a splitter. When one side of the input transformers secondary is swinging positive, that transistor is conducting while the other side of the center tap is swinging negative, pushing that transistor deep into cutoff. Drive power is not divided between transistors until a splitter is used.

Only one transistor at a time is ever contributing to the output power at any given time in a push-pull pair. Both transistors are not driven simultaneously due to the phase inversion through the input transformer. One transistor is always off (other than bias) while the other is on. One 2SC2879 can support a sustained collector current approaching 25 amps. No one will ever show a push-pull pair drawing close to 50 amps. Guaranteed!

 

[nomadradio]

The law of thermodynamics still applies. The input power to two push-pull transistors is split 50-50, minus circuit losses in the passive components.

73

 

[Shadetree Mechanic]

Each transistor in a push pull pair gets the full input power. But for only half the time. So they each average half power.

 

[kopcicle]

The three laws of thermodynamics still applies

FIFY

" 1) you can't win
2) you will loose
3) you have to play" *


* ~ not so anonymous, CR

To my mind it's instantaneous junction temperature that's the killer followed by inability to radiate heat into "heat soaked" sink.
TANSTAAFL

 

[nomadradio]

Actually I think you have the order of rules 2 and 3 reversed.

Still my favorite version of that idea.

73

 

[kopcicle]

rules 2 and 3 reversed

yup, edited for accuracy

 

[Shockwave]

Each transistor in a push pull pair gets the full input power. But for only half the time. So they each average half power.

That is how I understand it too. Since one of the two transistors will always be reverse biased when its drive swings negative, that transistor is essentially an open at that instant in time and consumes no drive power. The work load is split between the two parts but can never make more than the full output of one because only one works at a time.