I forgot mention, that on Rk of 6SN7 is really 123V. So Ug1 is around 1V (122V on anode 6SL7, and 123V on cathode 6SN7).
Tweaking values gives a bogey 6SN7 with a per triode loadline of 47k, and Vak max of 320V - 123V = 197V, and 0V crossing of 197/47k = 4.2mA, has a Vgk=0V limit of Vak=40V. So triode max Vpp swing is 197V - 40V = 157Vpp. The centre idle is circa Vak=120V, or 120+123 = 243V relative to 0V - which is much higher than the 196V shown on your circuit diagram.
123V on 27k = 4.6mA
(320V-196V)/47k = 2.6mA per triode, or 5.2mA into common cathode resistor.
Perhaps you have poor tolerance resistors for 47k and 27k, or leaky 6SN7 grids, or leaky coupling caps.
And as indicated earlier, the biasing of the 6SN7 triodes is perhaps too hot (with only Vak=196-123=73V at idle) and hence limiting the Vpp available for 807 driving. If valve rolling doesn't improve that situation, then you likely need to tube roll the 6SL7 to bring the anode voltage down, or re-bias that input stage to a lower anode voltage, or reduce the 27k tail value, or reduce the 47k supply dropper (or is that 22k now) to the PI stage to increase the available B+ from 320Vdc.
123V on 27k = 4.6mA
(320V-196V)/47k = 2.6mA per triode, or 5.2mA into common cathode resistor.
Perhaps you have poor tolerance resistors for 47k and 27k, or leaky 6SN7 grids, or leaky coupling caps.
And as indicated earlier, the biasing of the 6SN7 triodes is perhaps too hot (with only Vak=196-123=73V at idle) and hence limiting the Vpp available for 807 driving. If valve rolling doesn't improve that situation, then you likely need to tube roll the 6SL7 to bring the anode voltage down, or re-bias that input stage to a lower anode voltage, or reduce the 27k tail value, or reduce the 47k supply dropper (or is that 22k now) to the PI stage to increase the available B+ from 320Vdc.
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Agree with this, I suggested to reduce the 27k "tail" in post 15, but was not
able to edit it later, that gave no improvement he said, so it would probably
be better to reduce the 47k supply dropper. Not sure this has been tried before.
able to edit it later, that gave no improvement he said, so it would probably
be better to reduce the 47k supply dropper. Not sure this has been tried before.
zdenoeddie,
When are you going to measure the DCRs of the Primary and of the Secondary?
Be sure to short all the Secondary leads together when measuring the DCR of the Primary.
Be sure to short all the Primary leads together when measuring the DCR of the Secondary.
Please let us know the DCR measurement results.
When are you going to measure the DCRs of the Primary and of the Secondary?
Be sure to short all the Secondary leads together when measuring the DCR of the Primary.
Be sure to short all the Primary leads together when measuring the DCR of the Secondary.
Please let us know the DCR measurement results.