[HBR] HBR-11/2000. Comments?

[Walt Hutchens]

Dan said:
> The 12AX7 has been used as a modulator in zero bias, so it would be a good  
> candidate for AF output.  It reportedly gave about 7 watts  output.  
> Personally, I like a single 6AQ5, 6V6 or 7C5 with some  negative feedback like the Drake 
> 2B.  I don't like the class B pumping on  the B+ supply!

The 12AX7 in class B might make sense in a few applications 
where a whole lot of power is required -- a mobile modulator for 
example.  Like Dan, I don't want to challenge a receiver power 
supply with pulses that can go to a sizable chunk of an amp for 
even a few watts of output.   

The folks who want to use hi-fi speakers need to get over a watt to 
drive them; probably several watts would be better.    But for a 3-5" 
'communications' speaker, a fraction of a watt is plenty for same-
room listening.   The R8040A project uses half of a 12AU7 as an 
audio output stage driving a 3" speaker; it has plenty of loudness.   
The GC-HBR will be a push-pull 12AU7 with a 2x3" oval speaker.  
Both of those are class 'A,' so current drain is fairly constant.

Walt
KJ4KV