"John Byrns" wrote in message
...
In article , "Alex"
wrote:
"flipper" wrote in message
...
Funny you should mention it because I'm playing around with some dry
battery tubes and considered doing just that: screen feedback. I ended
up not including the pentode preamp in the loop, though.
Basically a toy at this stage but kinda cute, I think anyway.
http://flipperhome.dyndns.org/Batman.htm
Nice crcuit. I would remove (short out) redundant R11 (and reduce R10 to
maintain the overall gain). This would reduce AF voltage on the first
pentode 1N5GT plate.
Eliminating R11 appeals to my urge to minimize the parts count, but
beyond that what is the advantage reducing the AF voltage on the first
pentode 1N5GT plate? Is that the best thing to do, perhaps it would be
better to reduce the AF current on the first pentode 1N5GT plate?
Reducing AF voltage on the pentode plate will reduce AF current (and THD) as
well, because of reducing of AF current flowing through R8...
However, R11 decouples C9 + 1N5GT plate capacitance + wiring capacitance
from the grid of V1AA, thus helping stability. Thus, you are right, R11 may
be beneficial, and I am retracting my advice. Let R11 be there.
Another thing which is not "right" are C7 and C8, compensating OPT leakage
inductance. Instead of these caps, series RC circuits should be used, while
R and C are empirically adsjusted (as taught by our GURU and MASTER Mr
Partick Turner) for the best reproduction of a square wave. (For a start,
use R abou half of the optimum load Rpp). Zobel-like RCs will help
stability. I have been putting such Zobels in amps since the MASTER brought
it to my attention. With very good results. Stability (phase) margin never
hurts.
Regards,
Alex