Resistance Check Questions

[networkn]

Hi There!

I have some minor variance in the results, that I wanted to check please, before I head to voltage checking (Gulp!).

6) Says should be 2.4 K and is 2.5 K
7) Says should be 2.9 Kand is 2.944 K
9) Says should be 2.9 K and is 2.44 K
10) Says should be 2.4 K and is 2.5 K
13) Starts at 14 M counts slowly down then jumps to 50 K and climbs slowly UP?
B3) Says should be 2.9 K and is 2.944 K
B6) Says should be 2.9 K and is 2.44 K (I am wondering if this is a mistake in the manual and it should say should be 2.4 K) ? If it's really supposed to be 2.9 K Should I just resolder that joint?

Also I need to ask a particularly dumb question, how do I know whether the volume is all the way up or down?

Many thanks in advance.

[Paul Birkeland]

Hello Networkn,

Welcome to the forum!

Your resistance readings are all pretty close to the indicated values, so I wouldn't be concerned there.  When looking at resistances, we are mostly concerned about not seeing zeroes where they aren't supposed to be (this would be a short).

A 2.5K vs. 2.4K reading is just meter to meter variation, I think when we got 2.4K we had a meter that would give many digits, and it was something around 2.49K in actuality.

The reading at 13 is erratic because of interactions with the capacitor, if you left your meter attached to this point for long enough, I bet it would slowly climb to 270K (though it's hard to say for how long, as different meters will charge up that cap at different rates).

With the chassis plate facing up, turn the volume knob all the way counter clockwise to turn the volume all the way down.

I think you're ready to move on to voltage checks.

-PB

[networkn]

Hello Networkn,

Welcome to the forum!

Your resistance readings are all pretty close to the indicated values, so I wouldn't be concerned there.  When looking at resistances, we are mostly concerned about not seeing zeroes where they aren't supposed to be (this would be a short).

A 2.5K vs. 2.4K reading is just meter to meter variation, I think when we got 2.4K we had a meter that would give many digits, and it was something around 2.49K in actuality.

The reading at 13 is erratic because of interactions with the capacitor, if you left your meter attached to this point for long enough, I bet it would slowly climb to 270K (though it's hard to say for how long, as different meters will charge up that cap at different rates).

With the chassis plate facing up, turn the volume knob all the way counter clockwise to turn the volume all the way down.

I think you're ready to move on to voltage checks.

-PB

Hi There!

So I have some follow up questions:

1) In the photo I have linked, is this volume down?  (https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fs8.postimage.org%2Flfhuc5e75%2F20130104_213429.jpg&hash=9fd3fe1057b56ad8645e56e57a5703e4ef28a498)
2) How are you guys securing your rigs for the voltage checks? I can't find a stable way to do this? If I need to have in both of the tubes which are quite high, I can't rest it on the wood base (Which I haven't yet assembled) and I don't have a vice or anything.
3) I don't understand the instructions 5 and 6 on page 38. If I use the negative probe clip to connect to terminal 12, how can I connect the same lead to the ground buss?
4) How do I know which of my DMM settings is the 400V+ one? I have a V symbol which has a line and 3 dotted lines underneath and a V with a squigly line?
5) When it's on, is it safe to touch the bell metal top part of the transformer?

Sorry for the dumb questions, I thought it safer to check than risk getting it wrong, and me killed.

[Paul Birkeland]

1) In the photo I have linked, is this volume down?  (https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fs8.postimage.org%2Flfhuc5e75%2F20130104_213429.jpg&hash=9fd3fe1057b56ad8645e56e57a5703e4ef28a498)
2) How are you guys securing your rigs for the voltage checks? I can't find a stable way to do this? If I need to have in both of the tubes which are quite high, I can't rest it on the wood base (Which I haven't yet assembled) and I don't have a vice or anything.
3) I don't understand the instructions 5 and 6 on page 38. If I use the negative probe clip to connect to terminal 12, how can I connect the same lead to the ground buss?
4) How do I know which of my DMM settings is the 400V+ one? I have a V symbol which has a line and 3 dotted lines underneath and a V with a squigly line?
5) When it's on, is it safe to touch the bell metal top part of the transformer?

Sorry for the dumb questions, I thought it safer to check than risk getting it wrong, and me killed.

A photo of a knob can't determine if the pot is all the way down, you can loosen the screw and the knob can spin freely, so there is no way to know.  With the knob secured, turn it all the way counterclockwise, then the volume will be all the way down.

For voltage checks, having the base handy is nice.  You can use some wide blue painters' tape to hold it together temporarily, then flip the Crack over and place it in the base (the 6080 will be a little too tall, but not so much that it's a problem.

Your meter has two leads, clip the black one to the ground buss, take measurements with the red lead.  Terminal 12 is part of the ground buss, so that is what is recommended in the manual.  The suggestion in the manual is to use a test lead with alligator clips to make a more permanent connection between the black lead and terminal 12 (or the ground buss).

The V with the squiggly line is AC volts, the V with the solid and dashed lines is DC voltage.  If your meter has multiple ranges, you might see 2, 20, 200 as options, for the Crack, you'd want 200.  If your meter just has DC and 400 - then it is autoranging and you can leave it set there.

When the amp is on, the metal plate and transformer cover are connected to safety ground, so any shorts that would dump anything dangerous onto those parts will cause the fuse to blow, protecting you.

Here's kind of a sketchy video of how to use a meter

Feel free to write back if you have any additional questions, these are some important basics that can transfer to other facets of life.

-PB

[networkn]

Hi There!

Ok Here are my voltage check results. Something seems a little off

I will post the recommended amount and actual after it.
1) 90 | 77.2
2) 170 | 144
3) 0 | 0.1
4) 170 | 144
5) 90 | 77
6) Wildly going all over the place around 30-60
7) 100 | 94.6
0 | 1
9) 100 | 75
10) 0 | 90.1
11) 0 | 1.1
12) 0 | 0
13) 170 | 144
14) 0 | 0
15) 185 | 171
20) 0 | 0
21) 206 | 200
a1) 90 | 75.9
a2) 0 | 0
a3) 1.5 | 1.5
a4) 0 | 0
a5) 0 | 0
a6) 90 | 77
A7) 0 | 0
a8) 1.5 | 1.5
a9) 0 | 0

b1) 90 | 76
b2) 170 | 140
b3) 100 | 95
b4) 90 | 76
b5) 170 | 144
b6) 100 | 90
b7) 0 | 0
b8) 0 | 0

I guess the two I am most concerned about is 10 which is 90v over spec and 6

It does smell hot. I was concerned at first that it was something burning, but I could see no smoke per se. I am not sure if that's normal as the tubes heat for the first time or not.

Where should I start looking for causes?

Thanks once again.

[networkn]

http://s13.postimage.org/jou9kl1uv/20130107_223037.jpg

This what those two terminals primarily connect to. I am wondering if one of those resistors partially fried as they should look the same and one looks burned a little. The bottom one is giving 2.49KOhm Resistance Check, the other 2.20Kohm

[Paul Birkeland]

Yes, don't plug headphones into this Crack until 10/6 are under control.

As the 6080 begins to conduct, charge accumulates on the positive side of each of those 160uF capacitors, and current is drawn through the 2.49K resistors to charge these caps.

Current is not drawing through the 2.49K resistors, as you have ~90V sitting there waiting to be drawn down.

This could happen if the black wire going to your headphone jack is not properly tied into your ground buss.  The wiring on your jack looks OK to me, though that brown resistor makes me wonder about the 160uF caps, can you post a pic of the build in its entirety?

[networkn]

Thanks for the reply...

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fs9.postimage.org%2Fgrqxmfb0f%2F20130108_085046.jpg&hash=24cfb502f7d53a5fae000fcbead4e1396077fc46)
upload pics

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fs8.postimage.org%2Fbf9cjaov9%2F20130108_085025.jpg&hash=7b18546b694ce68e36c532212aa6df874fd51eca)
photo sharing sites

Are you talking about the black wire that runs between the Pot and the HP Jack? Should be pretty straightforward to resolder, but if it wasn't connected would the resistance readings have been off?

If I resolder do I need to redo the resistance checks ?

[Grainger49]

Ignore this if you have already done it.  Measure the resistance of each of the resistors on the headphone jack.  If one is burned it will be wrong.  That channel did something to molest the resistor.

As mentioned above the last thing back in the circuit is the electrolytic output cap that is supposed to protect the resistor from DC.  If that is bad, often but not always, a bad cap will have an end that bulges.  Those are the black caps on the B tube socket.

[networkn]

Ignore this if you have already done it.  Measure the resistance of each of the resistors on the headphone jack.  If one is burned it will be wrong.  That channel did something to molest the resistor.

As mentioned above the last thing back in the circuit is the electrolytic output cap that is supposed to protect the resistor from DC.  If that is bad, often but not always, a bad cap will have an end that bulges.  Those are the black caps on the B tube socket.

Hi There!

The resistor that goes from top left bottom right on the headphone jack is reading 2.20 as opposed to 2.49 as the other one measures. I'll try and get a better shot of it, but it looks not quite right. It definately looked identical when I soldered it, has it fried? If so is there something wrong early in the circuit or did I cook it when I soldered it?

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fs2.postimage.org%2Friflxu2i1%2F20130108_111041.jpg&hash=83e7e36b9bc9398448e86c6531fb09d95d20754f)
host images

[Grainger49]

Check that both of those are thousands of ohms.  The resistors are 2.49k ohms.  If one went bad and reads 2.2 ohms that is a problem.  But if it is just 2.2k ohms it won't make a difference.

Then look at the capacitors.

[networkn]

Check that both of those are thousands of ohms.  The resistors are 2.49k ohms.  If one went bad and reads 2.2 ohms that is a problem.  But if it is just 2.2k ohms it won't make a difference.

Then look at the capacitors.

Hi There!

Both are Definitely K-Ohms. I know before I switched it on to voltage, both read 2.49KOhms exactly, and notice it's looking burned, I presume that isn't normal. I can't see any bulging of the caps.

[Paul Birkeland]

Can you check to which terminals the pair of red and white wires attach that run to the headphone jack?  If those are miswired, you'd pass DC to the jack and heat up those resistors in a hurry.

[networkn]

Can you check to which terminals the pair of red and white wires attach that run to the headphone jack?  If those are miswired, you'd pass DC to the jack and heat up those resistors in a hurry.

Looking at the Jack with the pins facing you

White Cable Top Left to 10L (With a 249Kohm (Discoloured) Resistor connected to the Bottom Right.)
Red Cable Middle Left to 6L (With a 249Kohm (Normal looking) Resistor connect to the bottom right )

They seem very secure and well soldered.

[Paul Birkeland]

How about the wires that leave B3/B6?