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Ella circuit diagrams



Ella layout diagrams

Please note the following:
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These are NOT official layout diagrams. They are amended from those supplied by DIYhifiSupply when I built my kit in February 2005 and so are based on the Point-to-Point wired Ella. The older PCB version might use different components and the newer Ella models certainly do.
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The layouts shown do not match the original version. I have changed the wiring on tubes 1 and 2 so that they are identical while Brian's original versions had the triodes reversed. This is possible because the 6922 is a dual triode.

Valve pins

  Valve type
Pin 6922 6SN7 EL34/KT88
1 T2: Plate T2: Grid Grid 3 (Suppressor)
2 T2: Grid T2: Plate Heater
3 T2: Cathode T2: Cathode Plate
4 Heater T1: Grid Grid 2 (Screen)
5 Heater T1: Plate Grid 1
6 T1: Plate T1: Cathode -
7 T1: Grid Heater Heater
8 T1: Cathode Heater Cathode
9 Internal shield    

Normal Ella




Ella for Django Transformer Volume Control


NEVER connect a CD player or other source to the RCAs when wired like this! There is no volume control in the circuit so the amp will play at full volume.

Active Bias System


It was easiest to use a combination of the Django and Upgraded bias pot diagrams to draw this, but the ABS doesn't need either of these changes to be installed. Note that I've chosen to keep one of the existing 22K bias pots on each channel since it allows me to easily change the bias if I change between types of tubes (EL34, 6550 or KT88). So I have changed resistor R14 on the ABS to 7.5K, giving a maximum total resistance of 5.6K and a total maximum current of 60mA.

Upgraded bias pots


The pots have been wired here in reverse to the normal Ella. In this version turning the screw clockwise increases the measured bias voltage. If you prefer the original Ella version swap the red and black wires at each pot.

Ella biasing information
Normally set EL34s to around 35-45mA. This will sound OK and will give the tubes the maximum life. You can also bias up to about 50mA but then tube life starts to go down.

For the KT88/KT100 the bias should be around 45-60mA but shouldn't go over 60mA. Look out for red spots as a warning that the bias is too high.

On the Ella the bias is measured as a voltage. Since there is a 10ohm resistor on the cathode circuit the current can be calculated using the formula I=V/R. For example:

I = 0.42V / 10R = 0.042A = 42mA

(Note that 0.42V is the same as 420mV)

Ella as Triode with no Negative Feedback




Schottky diodes


Schottky

Negative bias diodes and bypass capacitors


NegBias

Screen diodes


ScreenDiode

or in triode mode:

ScreenDiode_Triode