Re: Feedback using parallel valves for summing



bill ramsay wrote:

On Fri, 09 Jun 2006 17:47:41 +0100, Pooh Bear
<rabbitsfriendsandrelations@xxxxxxxxxxx> wrote:



flipper wrote:

On Thu, 08 Jun 2006 18:30:32 GMT, "Ian Iveson"
<IanIveson.home@xxxxxxxxxxxxxxxx> wrote:

One thing I notice is that equal and opposite input signals result in an output
of double the frequency.

What you're seeing is the harmonic distortion of the two tubes that's
left after the primary signal has been nulled.

LMFAO ! Ian's not the brightest lad. His circuit produces no useful output. Hey !
Actually - it could be used as an intentional distortion generator. The audiohools
would love it.

Graham

Look smart arse, if people don't try things out, then they will
never find things out, so what if it does not work, in this game
it's trying out stuff that counts.

bill

You are actually quite right. Graham didn't get it.
Where you have an equal NFB voltage applied to a V1 conventional
SET input tube cathode and the anode, there is no difference voltage so no output
voltage either;
or at least very little, since the change of voltage between anode and cathode+grid
gives a change of Ia passing trough Ra, so some output is likely.
So what was there to laugh at?
The alternative being considered to using the the single input triode as a differential
device is to use 2 triodes with a
single RL but with input voltage of opposite phase as the NFB signal. If input = NFB
then you get no output
except a small amount of distortion that is a result of non +/- changes to gm for a
given equal input voltages.
But where the input voltage has slightly higher amplitude then an output voltage
sufficient to drive the amp to clipping is easily attainable. Any +ve Dn voltage
arriving at the NFB port is amplified by whatever gain is available and it can cancel
itself acording to the relevant NFB formulas.
Patrick Turner.

Methinks ARC use what they think is their own unique circuit which almost everyone
cannot understand and
then its easy for them to claim its *** hot.

Perhaps one of us could get a better outcome with less tubes but we just won't ever be
famous for it.

Its really difficult to be unique and different in 2006 about anything.

All the ways of connecting triodes have already been tried by someone else somewhere
sometime.


Patrick Turner

.