Plate resistor ?

[jamme61]

Do I have to use a plate resistor, if the voltage is right without one? I have an old fender where one side is stk fender other side is marshall 2204 preamp. on the one 12ax7 the voltage is 290 without adding a plate resistor. 290 is the voltage I need there for the cathode follower. do I have to add a plate resistor there for coupling or? Is OK to use no plate resistor? Thanks for any help

[John_P_WI]

Ummm in this configuration the plate r is needed. Otherwise the signal is shunted to ground though th power supply caps.

[Firestorm]

Right. The plate resistor isn't there to drop voltage, it's there to provide the range the signal needs to develop, from the voltage at the top of the resistor to the voltage at the bottom.

[matt h]

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[jamme61]

this is a fender bassman head aa867Layout (on normal side) with the bass side converted to marshall 2204 preamp. I assumed the dropping resistor in the can (you know where all the filter caps are) would act as my plate resistor? There's one spot on the board where the power comes in and all two 12ax7's are powered from. For V1A an V1B I have two 100K plate resistors (pin 1 and pin 6) dropping the voltage ( I think around 220volts each) On V2 which has the cathode follower on the one side(pin 6 side) I'm not using a plate resistor going to pin 6 (which gives me 290 volts without a plate resistor) pin 6 is connected to pin 1 via a 100K resistor. Everything sounds fine but was wondering if I should still put a resistor in there between the power source on the board and pin 6 ? Hope this explains it better sorry. Thanks again for the time on this.

[martin manning]

A schematic is worth a thousand words.

[matt h]

(deleted)

[jamme61]

If i'm understanding you (having extreme difficulty here) the following statements are true
You are talking about "v2" (third and fourth triodes of a 2203/4 preamp)
You are talking about pin6 which is the PLATE of the Cathode Follower (fourth triode of the preamp).


If those statements are true, do NOT use a plate resistor between pin6 and the filter cap node.

Triodes used as cathode followers DO NOT get plate resistors.

Matt thanks for figuring this out from my babble. Sorry to all you guys for not being able to explain this better. appreciate the help

[tubeswell]

A schematic is worth a thousand words.

[Bob-I]

It seems that you don't understand how a tube functions.

The tube varies the current. The plate resistor is there to convert current change to voltage change. V=IR so as the current changes across a constant resistance, the voltage will change.