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What is the theory of operation of the Super Twin Reverb 180w amp? (How does it work, not how do you work it.)
See attachment.
See attachment.
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-Bryan -
Judging by the looks of it, they just parallel the power tubes, and drew it that way for simplicity. -
How does the whole amp work. What does each part/section/stage do?-BryanComment
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It looks like any other amp to me, what areas are not clear to you?
V1A is a classic Fender front end, then through a classic Fender TMB tone stack and volume control with classic Fender recovery stage V1B. The extra contacts on the input jacks are just there to ground off the volume control when nothing is plugged in. All that does is mute at a later point in the circuit for better quieting. Marshall does something similar a lot.
From there, we go to V2A, an active EQ stage configured as a graphic or at least a multiband. We also branch through V2B, a pentode driving the reverb. 6CX8 is an odd tube for Fender, but the circuits are pretty conventional.
The reverb output rejoins the signal with the ooutput of the active EQ at mixer tube V3C. There is a switchable bias supply tap for the grid of this stage to cause distortion when selected. 6C10 is unusual for Fender, but it is just triodes. This distortion circuit sucks, in my humble view.
V3A is a cathode follower that is switchable in cathode circuit to be part of the distortion circuit. Exactly what they are doing there I'd have to think about.
From there the master volume feeds a conventional phase splitter, with an NFB kill footswitch used as a boost.
V5 is a CF drive stage for that forest of power tubes.
That is the best I can do right after a big lunch.Education is what you're left with after you have forgotten what you have learned.Comment
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Pin 2 of V1B is connected directly to the guitar input which seems bizzar especially since the tone stack is connected there too.-BryanComment
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No, it is not. Pin 2 is connected to ground through both switches of the input jacks. Less noise when no guitar is plugged in.Originally posted by tbryanh View PostComment
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As I said
The extra contacts on the input jacks are just there to ground off the volume control when nothing is plugged in. All that does is mute at a later point in the circuit for better quieting. Marshall does something similar a lot.Education is what you're left with after you have forgotten what you have learned.Comment
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I see that pin 2 of V1B is grounded when no guitars are plugged in, and the ground is interrupted when a guitar is plugged in.
But the bottom line is, the tip of the lower jack is always connected to pin 2 of V1B.
So when a guitar is plugged into the upper jack, the tip of the upper jack is connected to pin 2 of V1B.
Likewise, when a guitar is plugged into the lower jack, the tip of the lower jack is connected to pin 2 of V1B.
Also, when guitars are plugged into both the upper and lower jacks, the tip of the lower jack is connected to pin 2 of V1B.
This is what seems bizzar to me.
It must be that both switches open when only one guitar is plugged in. If this is the case, it is not shown schematically.-BryanComment
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No, the tip of the lower jack is never connected to pin 2 of V1B. So all your therefores after that point are rendered invalid.But the bottom line is, the tip of the lower jack is always connected to pin 2 of V1B.
The tip of the lower jack connects only through the 33k resistor to the pin7 of V1A.
Pin 2 at V1B, aside from its own circuit, is ONLY connected to the two cutout contacts on the jacks, and through them to ground.
WHat you are missing is that the two vertical lines from the tip contact to the switched contacts above it is a mechanical connection, NOT an electrical one. It represents the plastic mechanical lifter that actuates those contacts when the tip contact moves. There is no connection between those switched contacts and the tip contact.Education is what you're left with after you have forgotten what you have learned.Comment
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got it. thanks-BryanComment
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