Pot/Schem Question

[trem]

I am embarrassed to say, but.....
One thing (one of many) I never learned was to read how a Pot is connected via the schem.
For example...on the Princeton below...
1. The Speed Pot...does the arrow coked to the right mean the wiper is connected to the outside lug on the right side side.?

2. Speaking of that...what is right or left.?
Do I assume the schematic is looking at the pot from the players position...from the front of a functioning amp.?
Also...which way are the solder lugs oriented...straight up or straight down.?
(again, from the players perspective of a functioning amp.....or is THAT the wrong perspective.?)

Thank You Very Much

Fender - Fender Princeton Reverb AA1164 - ampix

[g1]

or is THAT the wrong perspective.?)

That's it .
The schematic is strictly an electrical representation of how it works. It doesn't really correspond to the physical dimension. For that you need a layout drawing.

[Enzo]

Yess^^^^

The schematic only shows the electrical relationships of the parts. The layout or "wiring diagram", shows the physical relationships of the parts.

If I swap the end wires on a pot, it will still work perfectly well, but it will work backwards. The pot itself is nothing more than a resistor with a contact you can slide along its length. More and more schematics are including a "CW" at one end to tell you which way it is wired, that is the clockwise end.

In the case of that speed control, the way the arrow is drawn says nothing about the ends. In fact, the control is wired as a variable resistor. We wire the wiper and one end into the circuit. Now the wiper determines the resistance. If we want to, we can wire the unused end leg back to the wiper.


If I am looking at a layout, it is fair to say left or right. but in general I try to stick with clockwise and counterclockwise. Then it doesn't matter what way the control is mounted.

[trem]

OH...OK.
I do understand the difference, electrically, between the schem and layout.....but I thought I may have been missing some additional info.
And yeah (again) that is why I asked...because I was wondering about which end to use to make the speed go from One (slow) to 10 (fast).

There again, if I really knew what was going on in the circuit, I would not have asked.....so I will ask now.
Does less resistance cause more (that is a little Feed-Back loop isn't it.?) signal to got to ground, and make for less speed.? .....or do I have it backward.?
I am not working on a Princeton, but I am robbing that circuit for a little low-watt (2x 6K6) head I am building.
Thank You

[J M Fahey]

I am embarrassed to say, but.....
One thing (one of many) I never learned was to read how a Pot is connected via the schem.
For example...on the Princeton below...
1. The Speed Pot...does the arrow coked to the right mean the wiper is connected to the outside lug on the right side side.?

1) you chose a quite fuzzy picture

2) and pot rotation way is not indicated on any of the pots there .

The diagonal arrow across the resistive element only means it's a variable resistance one, nothing else.
Often resistance is minimum or 0 with the pointer on 0 and max, whateverthe value, on 10 , but there are numerous exceptions, so that does not qualify as a rule.

2. Speaking of that...what is right or left.?
Do I assume the schematic is looking at the pot from the players position...from the front of a functioning amp.?
Also...which way are the solder lugs oriented...straight up or straight down.?
(again, from the players perspective of a functioning amp.....or is THAT the wrong perspective.?)

As said, that schematic does not show it, so let me find one which does.

[Enzo]

If there is still a question, the difference is more or less the difference between drawing someone a map to your house versus writing out directions.

In the case of a trem oscillator, the circuit is a phase sifter. A pulse at the plate of the triode runs through three R/C stages to the grid. and feedback loop is established.

Making those series caps larger slows it down, and smaller speeds it up. And likewise, making the resistors smaller speeds it up and larger resistance slows it down.

So in this case, wiring the control so it reduces resistance to speed it up ought to make the panel "right".

[trem]

OK...so I did have the Speed Pot backward...Thanks.
On another note.....the foot-switch. Is there any reason I cannot switch the Cathode To Ground connection.?
That is to say...turn the Trem on and off by breaking the ground connection at the cathode, and not at the oscillator circuit.?
Thank You

[Enzo]

It isn't a clear copy, Juan is right. However there is the second page which is the layout. That shows how they intended th wires to go.

[J M Fahey]

Up/down/right/left dont really matter

Pots are rotative and can be mounted on any position, besides knobs also have their little independent minds and scales can be drawn in any orientation so only certain thing is rotating clockwise or counterclockwise and seeing where the little sliding contact inside stops and which lug will it be touching.

Easy after the "click" in your mind.

For sanity, rotation is described as seen from the knob and shaft side.

So: looking at a pot (from the shaft side) , all 3 l3gs pointing up ... where is 0 and where is 10?
don't cheat, think a little
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if legs point up, and remember they are a forbidden zone for the slider, when rotating clockwise (which is usually 10) it will travel a big semicircle below, in fact 3/4 of a circle, and stop when it meets the top left leg.

So that leg is 10 , usually Hot in a volume or *amp* (not guitar ) tone pot .

And turning 3/4 counterclockwise, it will again travel below but going the other way and rest on the top right leg .
In a passive volume control it's usually ground (0) , also in tone controls which are really equalized volume controls such as James (Ampeg) or the treble control in Fender and Marshall.
In nhe tone controls it usually is not straight ground but goes there through a cap (so actually highs are muted).

Knowing that, now you understand this MesaBoogie V Twin which still does not use arrows, but writes a tiny little "cw"(clockwise) label close to one leg:

[Dave H]

Knowing that, now you understand this MesaBoogie V Twin which still does not use arrows, but writes a tiny little "cw"(clockwise) label close to one leg:

And then they carelessly draw the tone stack with the cw label of the lower pot right on the ccw leg of the pot above! It takes CAD to be that sloppy. You’d never do it on a hand drawn schematic.

[J M Fahey]

And then they carelessly draw the tone stack with the cw label of the lower pot right on the ccw leg of the pot above! It takes CAD to be that sloppy. You’d never do it on a hand drawn schematic.

Hey !!! It would be very easy otherwise !!!!
Where's the challenge???

[R.G.]

In the Schematic Drawers Guild, it's considered an indication of for what kind of reader the schematic is intended.

Schemos intended for replication by hand wirers or beginners will have "CW" and sometimes "CCW" also by the corresponding electrical points on the schematic.

Next step up is an arrow across the wiper, always pointing in the direction the wiper moves when the shaft is turned clockwise.

Next up is a dot by the CW pin, which can easily be missed or lost in reproduction.

Next up is no indication at all, these schematics being intended for readers who understand how the circuit works by looking at the schematic, and know which side of the pot is to be used for "clockwise" by knowing what the control does in the circuit and whether more or less resistance or wiper-division makes it go that way.

[g1]

the foot-switch. Is there any reason I cannot switch the Cathode To Ground connection.?
That is to say...turn the Trem on and off by breaking the ground connection at the cathode, and not at the oscillator circuit.?

I'm not sure about this one, I'm wondering about violating heater to cathode max voltage rating.

[trem]

I'm not sure about this one, I'm wondering about violating heater to cathode max voltage rating.

Oh Man...Sorry, but I am lost, but.....if I use the Cat Ground for my foot-switch...are you saying that will put the cathode at (or near) full B+ of the plate.?
I am actually using a 6SL7....I will have to look it up. Does anybody know off-hand.? Can the octal pre tubes handle that situation better.?
That never even occurred to me.
Thank You

[trem]

TDSL Tube data [6SL7]
.....It looks like 90 Volts if I am reading the data correctly.

But I stole it from an Ampeg schem that used a Cathode Foot-Switch.
I built a clone of the M12 and it has not had any problems (so far).
http://www.ampix.org/displayimage.ph..._display_media

So when I switched trem circuits, I was hoping to leave as much "stuff" right where it was at...which would mean keeping the cathode foot-switch. I suppose I can give it a try and see what happens.