One more question on this circuit, (thx for the first one Norm) The 50L6 (o/p tube) has a .02 cap going from the plate to it's cathode(which already has the usual 150 ohm resitor and 20mfd bypass cap to ground). When I remove this .02 cap, I lose some gain, and the plate voltage drops ~5 volts...Need some more help explaining what this cap is doing....

You are experiencing some oscillation, could be supersonic, and that's part of why this cap is here in the first place. BTY is it an .02 or .002?, and either way you want a 630v or 1 kv part here.

:One more question on this circuit, (thx for the first one Norm) The 50L6 (o/p tube) has a .02 cap going from the plate to it's cathode(which already has the usual 150 ohm resitor and 20mfd bypass cap to ground). When I remove this .02 cap, I lose some gain, and the plate voltage drops ~5 volts...Need some more help explaining what this cap is doing....
:

:You are experiencing some oscillation, could be supersonic, and that's part of why this cap is here in the first place. BTY is it an .02 or .002?, and either way you want a 630v or 1 kv part here.
:
::One more question on this circuit, (thx for the first one Norm) The 50L6 (o/p tube) has a .02 cap going from the plate to it's cathode(which already has the usual 150 ohm resitor and 20mfd bypass cap to ground). When I remove this .02 cap, I lose some gain, and the plate voltage drops ~5 volts...Need some more help explaining what this cap is doing....
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It's a .02 cap, factory original. If it was hi freq oscillation, I would think they would have used a .002 cap and sent it directly to ground. This cap goes to the + side of the cathode. Removing the cap actually decreases gain.

Agree the value is probably wrong. Whether the other end goes to the cathode or B- is not worth squabbling about. Thing is if you get oscillation, it draws power, and will load down the B+, and could do nasty things to several components. Lead dress of all components including those of the primary output transformer is sometimes critical.

::You are experiencing some oscillation, could be supersonic, and that's part of why this cap is here in the first place. BTY is it an .02 or .002?, and either way you want a 630v or 1 kv part here.
::
:::One more question on this circuit, (thx for the first one Norm) The 50L6 (o/p tube) has a .02 cap going from the plate to it's cathode(which already has the usual 150 ohm resitor and 20mfd bypass cap to ground). When I remove this .02 cap, I lose some gain, and the plate voltage drops ~5 volts...Need some more help explaining what this cap is doing....
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:It's a .02 cap, factory original. If it was hi freq oscillation, I would think they would have used a .002 cap and sent it directly to ground. This cap goes to the + side of the cathode. Removing the cap actually decreases gain.
:

Sometimes a cap is used from plate to cathode of the output tube for negative feedback. In this case cathode isn't bypassed to ground.

As mentioned a cap like this reduces high frequency response and unwanted oscillation. I would prefer the cap being connected between plate and screen, B+. If it shorts while connected to cathode radio components will be destroyed.

Norm

:Agree the value is probably wrong. Whether the other end goes to the cathode or B- is not worth squabbling about. Thing is if you get oscillation, it draws power, and will load down the B+, and could do nasty things to several components. Lead dress of all components including those of the primary output transformer is sometimes critical.
:
:::You are experiencing some oscillation, could be supersonic, and that's part of why this cap is here in the first place. BTY is it an .02 or .002?, and either way you want a 630v or 1 kv part here.
:::
::::One more question on this circuit, (thx for the first one Norm) The 50L6 (o/p tube) has a .02 cap going from the plate to it's cathode(which already has the usual 150 ohm resitor and 20mfd bypass cap to ground). When I remove this .02 cap, I lose some gain, and the plate voltage drops ~5 volts...Need some more help explaining what this cap is doing....
::::
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:::
::It's a .02 cap, factory original. If it was hi freq oscillation, I would think they would have used a .002 cap and sent it directly to ground. This cap goes to the + side of the cathode. Removing the cap actually decreases gain.
::
:
:

:Sometimes a cap is used from plate to cathode of the output tube for negative feedback. In this case cathode isn't bypassed to ground.
:
:As mentioned a cap like this reduces high frequency response and unwanted oscillation. I would prefer the cap being connected between plate and screen, B+. If it shorts while connected to cathode radio components will be destroyed.
:
:Norm
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Thanks for the suggestions guys...I think Norm's idea of neg feedback is on track..I'm going to do some 'experimenting' with the circuit and see if I understand what is in play here. This is the first one I've seen possibly using 2 NF circuits in a basic 2 tube audio circuit. I'm having fun learning, thanks to the help from you forum guys...I decided to start making schmatics of all my small phono amp circuits for future use when I want to modify an existing one for more power...Many of the 'one tube wonder' sets I repair and sell don't have enough 'oomph' with the modern .5 volt ceramic cartridges, and need a pre-amp tube added....Brian

I've seen that term here from time to time, but not sure what it means. Thanks.

Lead dress is how wires are routed under the chassis. If they are run around the wrong way it can cause oscillation or hum.

Norm

:I've seen that term here from time to time, but not sure what it means. Thanks.
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