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Help understanding a schematic

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jordyyy

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Can anyone help me understand what is going on with this part of the schematic?


Is the top left resistor a 2.26k also? is the bottom left resistor part of the pot? where does it connect to? What do the 4 dots mean?

Thanks
 

Reloadron

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It looks like a "ganged" 50K pot to me. Meaning actually two 50K post with a single shaft.

Ron
 

bychon

New Member
Ahhh...yep. Two resistors at 2.26k and two pots mechanically tied together. It's a stereo current buffer with no plate limiting resistors and the kathode resistors are allowed to be anything from 2.26k to 52.26k.
 

jordyyy

New Member
So it should actually be drawn like this image on the right?



Also, which side is the + on the polarized capacitors?
 
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bychon

New Member
You left out the 2.26k resistors between the pots and ground and the pots do not have one end tied to the circuit. Your drawing is wrong on two counts. The kathodes are attached at the wipers.
As for the capacitors, every voltage in your circuit is positive so the plusitive side of the cap must face the circuity and the minusitive side goes to ground.
 

Reloadron

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So it should actually be drawn like this image on the right?



Also, which side is the + on the polarized capacitors?
Another detail with the pot configuration on the right. Drawn as you have it drawn decreasing the left out signal will be increasing the right out signal. If you use a ganged or mechanically linked pots make sure the resistive change is the same for each in the same direction. Also as to the triode tube (valve) I think the pot outputs (wipers) should be tied to the grids. There should be more to the tube (valve) stage correct?

Ron
 

bychon

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No, there isn't more to the tube stage. It is a current buffer and putting the output volume controls on the grids would make it useless.
 

Reloadron

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No, there isn't more to the tube stage. It is a current buffer and putting the output volume controls on the grids would make it useless.
Wouldn't that make it a cathode follower configuration? Signal in on Grid and out on Cathode? Just curious. If the signal in was applied to the cathodes where would the signal out come from?

Ron
 

bychon

New Member
It is a cathode follower. The input jacks are connected to the grids. The out put (volume) controls are connected to the cathodes. All this is good.

If you applied the signal to the cathodes, you would ground the grid and the out put would magically appear at the plate..right after you add a plate resistor.

Tubes just don't produce much power on their grids. That's why grids are not used as the output.
 

Reloadron

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That is what I said:

Also as to the triode tube (valve) I think the pot outputs (wipers) should be tied to the grids. There should be more to the tube (valve) stage correct?
I was questioning what was said here:

No, there isn't more to the tube stage. It is a current buffer and putting the output volume controls on the grids would make it useless.
Anyway, the tube portion shows next to nothing including as you mentioned a plate resistor, really sort of nothing there. I see it as the outputs J3 & J4 (the pot wipers as outputs) going to the grids and the signal taken off the cathodes.

Matters not as the OP hasn't been back.

Ron
 

bychon

New Member
The pot wipers are connected to the cathodes and the output jacks (J3 and J4). Yes, the signal is being taken off the cathodes which are connected to the pot wipers and the outputs. The grids are connected to J1 and J2. Whatever signal arrives, it arrives at the grids, which are like the gate of a MOSFET. Very very high impedance grids (gates). The grids allow current to flow through the valves and out the cathodes (or in, depending on how you think). More current as the grids become more positive. Much like a j-fet, the tube has some current flowing at zero voltage from grid to cathode. When the grids become more positive, more current flows and the resulting current through the cathode resistors developes a more positive voltage at the cathode. Thus, the voltage at the cathodes follow the voltage at the grids. The voltages will be almost exactly the same if the cathode resistors have enough resistance, and the tube tends to keep zero difference from grid to cathode. As the cathode resistors are adjusted to less and less resistance, the tube does not allow enough current to keep the grid to cathode voltage zero. The grids become more positive than the cathodes and the resultant increased difference turns the tubes on more fully. Thus, you have a common emitter, voltage follower circuit with no collector resistors.
 
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