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RE: PDF DOCUMENTATION OF DIGITAL TUBE STAGE!

I done some calculation of the circuit according the tube data and textbook reference:

6n14P data: http://frank.pocnet.net/sheets/113/6/6N14P.pdf

mu=25 S=6.8 Ra = mu/S = 3.67K


Output impedance of a cathode follower

Rout = Ra / mu+1

= 3.67K / 26 = 141 ohm

Voltage gain of a cathode follower

Where Rk= (75+75)=150 ohm

V= (mu * Rk) / (Ra + (mu+1)*Rk) = 3750/7570 = 0.495


With a 3.3V input, this output will be about 0.4V PP.


I built the circuit to test its performance. Since I don't have any 6n14P, I used an equivalant tube, ECC84, instead.



Below pix showed the signal at the input (upper trace) and the tube output
(lower trace). The singal was drawn directly from the FPGA and hex inverter(74hcxx)was removed. No loading was applied to the tube output.





Below pix showed the signal at the input (upper trace) and the tube output
(lower trace) wuth a 75 ohm resistive load applied.





Great! This tube buffer can handle a 75 ohm load, albeit at a reduced output(about 0.32V PP). Not bad for such a simple buffer circuit.

By the way, LGA 775, there are some mistakes on the power supply circuit.

The bridge rectifier was not correctly connected, and AC is applied directly to the caps.

I do not know the application of the voltage stablizer in your circuit as it was placed in series with the B+ rail. It is supposed to be connected in parellel with the PS so as to stabilize voltage. It acts like a shunt regulator and a resisitor needs to be put in series with it whereas the cap in parellel should suitably reduced. More, if it is intended to be used as a shunt reg. the rating of 75V does not seem sufficient for this circuit. 125V would be better. please clarify.

Finally, the filament needs a voltage reference. In this case, reference to the ground.


Edits: 06/21/10 06/21/10 06/21/10 06/21/10 06/21/10 06/21/10 06/21/10 06/21/10
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