Path of least resistance/Path closest to ground

[TurbOSquiD77]

In regards to which direction the outer foil on caps should face, I'm trying to find the path of least resistance in a few locations. How do we find the path of least resistance?
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I've been doing this:
Amp powered off.
All parts connected including tubes.
Measure the resistance at each terminal of a connected capacitor.
Whichever terminal shows the lower value of resistance, this is the path of least resistance, and the outer foil should be connected to that terminal.
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Example:
Crack/C2A output caps - terminals 5/15 show a lower resistance.
C2A 2.2uF small board "x" shows lower resistance. Haven't measured the .1uF's quite yet. 
S.E.X. interstage terminals 4/18 show lower resistance, and coupling cap terminals 3/17 show lower resistance.
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Will by practice yield correct results showing that this is the path of least resistance on each of these positions, whether the cap is on the C4S boards or not?

Thanks

-T

 

[Paul Joppa]

It's not low resistance that you want, it's the lowest impedance at audio frequencies in the operating circuit. Unfortunately, you can't measure that with a voltmeter.

In most cases, that will be the signal source for audio path caps. Power supply caps  are usually grounded, which would be the place for the outer foil - except for the first stage of the voltage doubler circuit we use in many of our amps.

Best to ask on the forum for a specific application, if you don't yet have enough engineering knowledge to make it obvious.

 

[TurbOSquiD77]

Thanks PJ

I took a stab at it the other night, and after staring at the schematics while comparing to the physical amplifier I might have figured it out.

Crackatwoa:
100uF Output Coupling Caps = outer foil to terminals 10/20, inside foil towards headphone jack.
.1uF Low Current Board = outer foil to -reg, inside foil towards the 220 ohm resistor because the signal is coming in at -reg from the volume control.
2.2uF Low Current Board = outer foil to +reg, inside foil to x. This one I had the most trouble with. I see that the reference, or input of the TL431 is "r" which tells me the signal enters here. So coming from +reg through the 2.2uF to x, passing the 147k resistor to hit the 2.49k resistor, and into the TL431. Then out the cathode of the TL431 to the cathode of the 6AQ5. Or I'm completely backwards. Or it's opposite on either side I'm not quite sure here. The red wire from +reg, and black wire from -reg were throwing me off.


S.E.X.:
1.5uF Coupling Caps = outer foil to terminals 10/24 because the signal is coming from the plate chokes, through the 1.5uF caps, and to the output transformers.
.1uF Interstage Caps = outer foil to terminals 2/16 because the outer foil should face the plate of the tube maybe? Otherwise I'm not quite sure why, but that's what I've got. 

May I have feedback on my findings? As always I greatly appreciate feedback from anyone and everyone!

 

[Paul Joppa]

I don't see any 2.2uF caps in the C2A manual - PB will have to answer about that, it's his design.

Otherwise your descriptions appear correct to me - good job!

 

[Paul Birkeland]

2.2uF Low Current Board = outer foil to +reg, inside foil to x. This one I had the most trouble with. I see that the reference, or input of the TL431 is "r" which tells me the signal enters here. So coming from +reg through the 2.2uF to x, passing the 147k resistor to hit the 2.49k resistor, and into the TL431. Then out the cathode of the TL431 to the cathode of the 6AQ5. Or I'm completely backwards. Or it's opposite on either side I'm not quite sure here. The red wire from +reg, and black wire from -reg were throwing me off.

I would say that the end going to "X" is the end that's the lowest impedance to ground.

 

[TurbOSquiD77]

For lack of along, more detailed question.... why?