[Amps] AB1, AB2, Audio and RF amps

skipp isaham nospam4me@juno.com
Sun, 1 Dec 2002 19:51:21 -0800


Way too much turkey over the holiday...
- 
Hi groovy guys and gals...
- 
Re:  AB1, AB2, Audio and Radio Frequency Amplifiers. 
-
For the topic example, know there are two different 
conventional layouts for grid driven AB1 operation, one 
for audio, the other for RF. 
-
Classic guitar amplifier AB1 circuits are often push 
pull layouts with phase inverters and high impedance 
"grid circuits" (relative to RF amplifiers).  Depending on 
the method of bias, often a negative potential is 
applied through the grid resistors which can be 100K 
or more. 
-
We overdrive the tube guitar amplifier, it becomes 
"AB2 as best possible", within the confines of the 
circuit and its mix of contributing factors. 
-
You might assume AB2 to be the consumption of 
drive power (grid current) , which is possible through 
AC circuits.   It does happen in audio circuits. 
- 
Some of us pay big money for the end result 
through Celestian Speakers.  
- 
AB1 designed RF amplifiers often have a much lower 
input (swamped) impedance, care and feeding issues 
abound because the transition to AB2 operation is most 
often unwanted.  We do not see push pull RF 
amplifiers much anymore. 
- 
For the most part, both audio and radio frequency 
AB1 amplifiers are AC coupled unless someone 
is paying big money for true DC operation. 
- 
My Krell 50watt output  dc coupled stereo audio 
amplifier makes a nice room heater... outputs 
about 500+ watts of heat anytime the switch is 
up.  DC coupled amplifiers are not always "cool". 
-
cheers
skipp
-
-
>> >> So an AB1 amp can be AB2 if it is over driven, and 
>> >> an AB2 amp can be an
>> >> AB1 amp if it under driven?
>> >
>> >Nonsense.
>> >
>> **  please explain
>
>You can build an audio amp or modulator that is capacitively coupled
>to the grids of the output tube and there is nothing you can do to drive
>it into AB2 (grid current). 
: How is DC grid bias applied to the grids?
>You have to DC couple it or use a transformer to
>drive it into grid current.
>Either the circuit supports AB2 or it doesn't.
>> >>
>> >> How would you design an AB1 amp that can not be over driven?
>> >>
>> >> -  Rich...,


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