Well I finally got my act together and took a look at all your helpful
suggestions for my dynacord eminent to b able to overdrive nicely...

It seems that there were 2 things that really helped (although I'll have to
have another listen tomorrow when my ears are fresh - amazing how many
people forget that)

1) the output stage was re-rigged along Marshall lines so the draw per valve
is a fair bit lower.
2) The Bias DIODE was on it's way out and has been replaced with a 1n4007 -
my suspicions were raised when the bias was adjusted to -40V last week and
then the last bit left on the bias trim pots was needed for adjusting for a
different pair this week...

The capacitors were changed but that didn't resolve the problem - it was
simply too much conduction in the EL34's and a weakening bias supply.

As usual though, one problem is resolved and another appears... the B+
supply now drops by more than 60V in really heavy overdrive without sounding
like someone's just turned off the amp. It seems that these valves won't
play ball nicely with a supply of less than 360V where it bottoms out now.
Before this drooped to 290V and sounded BAD. The bias is also more
controlable and the supply has risen from 400V to 440V with the reduced EL34
current draw.

Here's the wierdo though.... on one side the Bias sags by up to 1V and the
other RISES by 8-9V!!!!! this is valve independant as I switched the valves
over and tried a different pair in the amp...

After all that, the negative feedback wasn't really at fault...

Thanks for the suggestions guys... any idea though what's up with the bias?

cb

PS. As I mentioned before, rec.audio.tubes beats alt.guitar.amps hands
down... I posted the same questions there and only received 1 suggestion
about raising the supply capacitances.... It's all electioneering there -
Keep up the good work guys!

"Chris Berry" wrote in message
...
Well I finally got my act together and took a look at all your helpful
suggestions for my dynacord eminent to b able to overdrive nicely...

It seems that there were 2 things that really helped (although I'll have
to
have another listen tomorrow when my ears are fresh - amazing how many
people forget that)

1) the output stage was re-rigged along Marshall lines so the draw per
valve
is a fair bit lower.
2) The Bias DIODE was on it's way out and has been replaced with a
1n4007 -
my suspicions were raised when the bias was adjusted to -40V last week and
then the last bit left on the bias trim pots was needed for adjusting for
a
different pair this week...

The capacitors were changed but that didn't resolve the problem - it was
simply too much conduction in the EL34's and a weakening bias supply.

As usual though, one problem is resolved and another appears... the B+
supply now drops by more than 60V in really heavy overdrive without
sounding
like someone's just turned off the amp. It seems that these valves won't
play ball nicely with a supply of less than 360V where it bottoms out now.
Before this drooped to 290V and sounded BAD. The bias is also more
controlable and the supply has risen from 400V to 440V with the reduced
EL34
current draw.

Here's the wierdo though.... on one side the Bias sags by up to 1V and the
other RISES by 8-9V!!!!! this is valve independant as I switched the
valves
over and tried a different pair in the amp...

Perhaps not an anomaly, I bet the side driven by the cathode of the phase
splitter
sags more. Is it ?
(I suppose you checked the EL34 grid resistor for drift)

Cheers, Yves.


After all that, the negative feedback wasn't really at fault...

Thanks for the suggestions guys... any idea though what's up with the
bias?

cb

PS. As I mentioned before, rec.audio.tubes beats alt.guitar.amps hands
down... I posted the same questions there and only received 1 suggestion
about raising the supply capacitances.... It's all electioneering there -
Keep up the good work guys!