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Hello my friends!
At last, I disconnected the choke (it is exactly not a part of 5E9-A
schem anyway).
As a result, the B+ (first filter capacitor) is now 375V. The voltage
at the power tube plates is a couple of volts below that, and the
screen grids is a couple of volts below that. There is more headroom,
it breaks up not so early, the sound is a little bit more aggressive.
So, it helps and the sound seems to be OK!?
However, 6V6‘s cathodes are now about 24V at each power valve (Fender
Schem suggests 27,5V) and the current measured from cathode to ground
(with 1R resistors on each cathode) per tube is 45mA (it means that at
the moment the output tubes are biased to deliver 45mA).
And I don't know if it is correct because I have read many reports
which suggest only 22,5 - 31mA at those kinds of amps.
My question is how can this influence the sound of the amp? Shouldn't
I reduce that?
I read also the opinion that seeing how 5E9-A Tremolux circuit have
non-adjustable biasing (self biasing cathode bias in the case of the
5E9-A) the appropriate tubes voltage should not be an issue and the
bias voltage for power tubes is only really an issue for amps with a
fixed adjustable bias because the bias voltage is already being
balanced by the components in the amp!??
Finally, what kind of power tubes you would recommend for the amp?
Now, I am using JJ tubes, only at V1 I have an old black plate 12AY7.
Are there any which would handle more treble and more headroom? BTW I
mean especially the power tubes.
thanks
Martin
At last, I disconnected the choke (it is exactly not a part of 5E9-A
schem anyway).
As a result, the B+ (first filter capacitor) is now 375V. The voltage
at the power tube plates is a couple of volts below that, and the
screen grids is a couple of volts below that. There is more headroom,
it breaks up not so early, the sound is a little bit more aggressive.
So, it helps and the sound seems to be OK!?
However, 6V6‘s cathodes are now about 24V at each power valve (Fender
Schem suggests 27,5V) and the current measured from cathode to ground
(with 1R resistors on each cathode) per tube is 45mA (it means that at
the moment the output tubes are biased to deliver 45mA).
And I don't know if it is correct because I have read many reports
which suggest only 22,5 - 31mA at those kinds of amps.
My question is how can this influence the sound of the amp? Shouldn't
I reduce that?
I read also the opinion that seeing how 5E9-A Tremolux circuit have
non-adjustable biasing (self biasing cathode bias in the case of the
5E9-A) the appropriate tubes voltage should not be an issue and the
bias voltage for power tubes is only really an issue for amps with a
fixed adjustable bias because the bias voltage is already being
balanced by the components in the amp!??
Finally, what kind of power tubes you would recommend for the amp?
Now, I am using JJ tubes, only at V1 I have an old black plate 12AY7.
Are there any which would handle more treble and more headroom? BTW I
mean especially the power tubes.
thanks
Martin