weird ef86 input stage in a Philips amp

[honinbou]

According to the schematic diagram of this AG9014 integrated amplifier the suppressor grid of EF86 (pin 8) is currently grounded. The decoupling screen cap is 8uF electrolytic not the common 0.47-2uf film. Cathode decoupling capacitor is 100uF. It is definitely some extraordinary EF86 connection.

Besides costcutting there has to be another reason why Philips engineers end up with this iteration of the phono input stage...

[llwhtt]

I would say it's to get more gain. Most pentode input stages have the small film connected between the screen and cathode, less gain.

Craig

[ray_moth]

I agree that it's an unusually large capacitance for a screen bypass cap, but the connection to ground instead of to the cathode is quite normal. Since the cathode has its own bypass cap, it won't make any difference. If the cathode were not bypassed, then you would get some positive FB.

[llwhtt]

Ray Moth you caught that, usually when the screen is connected to the cathode thru a capacitor the cathode is not bypassed. I thought of that about five minutes after I hit the button.

Craig

[honinbou]

thanks I learn something new today