[günther]

The difference in the resistance is OK. I see the same on my trafo.
Next point to check is the heater. Both filaments working?
Try to check the current in the heater circuit. Voltage readings are not helpful in this case.

[Mjork]

OK, this is something I did not try yet.

If I disconnect the filament wiring from all tubes en make a loop over just the ECC99 pins 4+5 and pin 9 I get 6.6VAC between the pins and the current through the MM shows 5.1mA flow through the circuit. Both the heaters are glowing in the tube. When taking the 12AY7 I see approx the same values

Is that a correct value?

[Dirk]

R23 and R24 are both connected to ground ? Both pins in the tube socket are not damaged and the tube pins are having a good connection with the socket. The value of both resistors is correct ? Checked it with a DMM ?
I would say that one system of the tube is not working correctly and I would check all connections and components which are connected with the ECC99 first.

If you swap the blue and brown wire of the OT does the misformed half wave stays at the same position or does it move to the other half of the sine wave ?

Best regards, Dirk

[Dirk]

Oh, I though one of the pictures which you posted of the scope shows both plates together but it doesn't. It would be good to see both plates together too.

Best regards, Dirk

[Mjork]

R23 and 24 are connected to ground: yes
Tube and pins look OK, i have a second ECC99 and the curves did not change
all resistors I did check with a DMM indeed

Have not tried swapping blue and brown yet.

The pic showing both plates together is attached

[günther]

?...through the MM shows 5.1mA flow through the circuit.
MM no idea
Anyway,  the heaterloop runs at 300mA + 300mA + 800mA + 30mA ~ 1430mA. 30 mA is for the two 100Ohm resitors.
Don't know your skills, so let me Show up an easier way.

Disconnect the wires from pin 9
Disconnect the bridge betwenn pin 4 and 5

Now test the resitance betwenn pin 9 and 4. Should be less than 5 Ohm for a cold tube
Do the same with pin 9 and 5. Should also be less than 5 Ohm.

If you see these values,  the connection from the Socket to the tube is OK. Current can flow.


 

[Mjork]

MM = DMM
I also expected higher currents. spec sheet gives 300mA at 6.6V also.
Verified with a loose power supply, 10VAC, and got approx the same values.
It must be something with the DMM settings. Drives me mad but I cannot find it.
My other DMM does not measure current at AC so cannot check.

Anyway, the resistance I checked. Pins 9 to 4 and 9 to 5 are both around 2.6 Ohm when really cold,

[günther]

What DMM Model you use?

For the next step to solve that Problem we need two 10k resistor. 1watt or more would be nice.

[Dirk]

Do you have a connection between the two grids ?

You have tested an other ECC99 with the same result so the tube should not be the problem.
I guess if you de-solder the wire which connect s grid 1 OR grid 2 of the ECC99 the amp works (of course only with half power). You should do this too to test both sides of the output transformer
If both wires are connected the amp does not work because both systems of the ECC99 are "on" at the same time. This is what the scope shows (if the measurement is correct).
The PI seams to work correctly too so I could imagine that you have a connection between the two grids which causes that both systems of the ECC99 are working in parallel.

Best regards, Dirk

[günther]

When I swap two Wires on the primary side of output trafo, the plate signal shows similar behavior as your amp.

[Mjork]

I have swapped the blue and the brown wire (the input sides of the trafo, but the result is the same.

Disconnecting one side of the trafo shows as per attached pic. Both waves are identical sine shape  and the plate is 40VAC with the grid at 15VAC.
So now there is amplification in that final stage and the dent in the wave is gone.

[günther]

For an 8 ohm speaker you use 4 and 6 ?

[Dirk]

Disconnecting one side of the trafo shows as per attached pic.

And the other side ? How does it look when you disconnect the second plate and connect the first again ? It should look the same just mirrored. Does it ?
Did you check if you have a connection somewhere between the two grids of the ECC99 ? Maybe somewhere on the board or at the socket ?

Best regards, Dirk

PS: I have also some PCBs of the Emma (not online yet) which is more failsave to use. If you are not able to find the mistake to use the PCB is another option because you do not have to make any onboard connections. But you should try to improve the soldering point and short the wires regardless what you use.

[cca88]

Ähmm
may throw the possibility of "grid current" back into the discussion?

Let me guess - the output of the cathodyne which is showing the spike is the anode connection...

Kirchoff tells us, that the signal at the two working resistors of the cathodyne have to behave equal, under the assumption that there is no current leaving the circuit.

Jochen

PS: try to use PSPICE Tube Models which simulate grid current condition. In the PSPICE SEction of the forum - look for the latest models of Thaddäeus...  They might provide this feature. I have not tried them yet, but i am confident.

[Mjork]

@ Gunter: 8 ohm speaker, connection 4 and 6 indeed

@Dirk: other side looks almost the same, not mirrored, but bit flattened though, see pic. But that does not really mean anything as it depends from what point the signal is picked up, sometimes I see the signal just flip while measuring.
So to chech if they are mirrored I disconnected both plates from the trafo. Then looked at the signal on the plate (induced signal?) Then you can see they are opposed to eachother, see other pic.
Thanks for offering the PCB but I will first lift the board from the housing again and check/redo the soldering of the  6 resistors and interconnections. Something for the coming friday.

@ cca88: the signals after the PI are nice sines and 100% mirrored from eachother.