In article ,
Patrick Turner wrote:
[Snip]
So what happens when we use a 5k load on the same amp?
The same idle current flows, and the same range of Ia variation 0f +/-
45mA will define the
class A **current** swing, ( where the **current** wave THD 5% and
mainly all 2H ).
So the class A load on each tube = 1/2 x 5k = 2.5k, so the maximum class
A V swing at each anode
= 2,500ohms x 0.045A pk = 112.5Vpk = 225pk from anode to anode, or
159vrms across 5k,
giving 5 watts of class A.
But the load value allows for a much larger increase in Ia than the 50mA
of maximum decrease in Ia.
This also means that once the Ia travels below 10% of the idle value,
the gm of the tube cutting off
has diminished to such a low value the other tube turning on harder is
providing virtually all the Ichange x Vchange
across the available load, and is the only device coupled through only
1/2 the OPT primary
to the load, so the RL seen by this tube turning on hard has reduced to
1/2 its class A load,
or 1/4 of the nominal RL a-a, and in this case its 1.25k.
The load is the same as that for a class B amp.
Isn't 1.25k too low a load for getting maximum power from a KT88 in
triode mode, even in class B?
[Snip]
Anyway, the quad of 6550 while working in class A with a 10ohm load
connected
across the mis-labelled 0-4 ohm outlet do sound VERY well.
Those wanting a schematic of what have done may ask as I have a .gif
available.
Its much simpler than the original, and I won't beak ARC rules by
handing out free copies of their
abominable concoctious junk.
What is all this talk about ARC's anyone else's rules that would keep
you from handing out free copies of their abominable concoctious junk,
assuming you drew the schematic your self? You mentioned this same
issue in connection with the ManleyLabs amplifier you modified, my
understanding is that they only have protection for schematics they have
drawn, if you draw your own schematic of the same circuit, they have no
rights with regard to it. Any Lawyers out there care to comment?
[Snip]
The VT100 had a true horror for a PSU and after fitting a CLC B+ filter
and re-locating
earth paths, I finally got hum&noises to be less than 1mV with preamp
gain at max with
open cd input.
Is this on the 4 Ohm tap? If so it is only 66 dB below 1 Watt, or 69 dB
with an 8 Ohm speaker connected to the 4 Ohm tap, not an awe inspiring
result, but apparently typical for many tube amps. But maybe it's not
so bad with the preamp included, did you measure the hum&noises of the
VT100 alone?
Regards,
John Byrns
--
Surf my web pages at,
http://fmamradios.com/