My voltages are about twice what they should be [resolved]

[larmader]

Hi all,

I've just finished my crack build, and checked the voltages.  All of my voltages are roughly double the range specified for the terminals 1-10.  Any ideas what causes this.  I'm suspicious of the smaller tube, as I only saw one glowing point in it light up originally, and now I'm not sure I'm seeing anything glowing in it.

Thanks!
Lar

 

[Paul Birkeland]

Can you post your voltages?

What did you measure for your incoming AC voltage and which voltage range did you select when wiring up your kit?

 

[larmader]

1) 175
2) 400
3) 0
4) 400
5) 175
6) 0
7) 220
8) 0
9)220
10) 0

The incoming AC voltage measured 122 volts, so I selected the greater than 115 and less than 130 option.

 

[Paul Birkeland]

It is most likely that one of the black wires connecting to the headphone jack is loose.

It also looks like the wire at A4 is loose, and this would cause one LED to not light up. 

 

[larmader]

Thanks so much for jumping in on this!

Well, I checked the headphone jack wires, and A4.  They looked ok, but I resoldered them anyway.  Still the same voltage readings.

Both of the LEDs in the circuit light up. What I meant was that I had originally thought that the smaller tube wasn't glowing, but I turned out the lights and was able to see two very small glowing points inside the tube.  So the tube seems ok.

I really appreciate you taking the time to look at this.  Let me know if you have any other ideas to try!
Lar

 

[Paul Birkeland]

The black wires that are connected to the 2 6-lug strips, then the headphone jack, then the front 5 lug strip aren't properly connected.  We have seen this exact problem before, and most of the time it is the junction of the black wires at the headphone jack, but it sounds like in your case you need to check all of the places where those black wires connect.  Reheating all of those joints is probably a fine idea.  There are only about five or six joints, so it's not too big of a job. 

 

[larmader]

Well, something went very wrong    I was reviewing each of the steps of my work, and was in the process of reviewing the final resistances when something sparked and went POP and a puff of smoke emerged from near my test lead at 12U.  I really don't think the test lead bumped anything else; this seemed rather spontaneous.  I think it might have been one of the two big brown capacitors located there, although it could just as easily been one of the two resistors in there.  Any way to determine which is faulty?  Or do I just reorder a bunch of components and replace them?  Dang.  Thanks for any ideas.  #ampbuildingfail

 

[Paul Birkeland]

There isn't likely to be anything to replace after this incident, but I would recommend going through and tugging on each end of each black wire back there and up front until you find the loose wire.

 

[larmader]

Ok, that's somewhat reassuring

Well, I went over all of those wires and they seem solidly connected.  I reheated all of the connections for the black wires.  I went through all of the build steps to be sure I didn't mis-wire something, and all seems ok.

Well, I want to back up a sec and double check my resistance readings.  For all of the terminals that are supposed to read 2.9k Ohms (terminals 7, 9, B3, B6), I get infinity, if I'm reading this meter correctly (I have a cheap digital meter.  On this meter, the display shows 1 and the low battery symbol lights up, seemingly to indicate infinity).  Changing the range of the meter has no effect in this case.  As a point of reference, I do get the proper values for the center pin of the rca jack; I'm getting roughly 95k Ohms.  Also, all of the terminals that are supposed to read * (which I understand to mean varying), also read infinity.

So this seems wrong to me.

Thanks again for your help.

 

[Paul Birkeland]

For all of the terminals that are supposed to read 2.9k Ohms (terminals 7, 9, B3, B6), I get infinity

What resistance do you get for terminal 3?

 

[larmader]

I get 0 Ohms at the terminals that are supposed to read 0 (terminals 3, 6, 8, 10, 12, 14, 20, 22).

 

[larmader]

ok, I'm an idiot.  I am getting the proper resistance at all of the terminals, including the 2.9k Ohms terminals.  Sorry for the false alarm.

 

[larmader]

So, as a summary of where I think I am at, I think I am back to square one. I am still seeing the voltages at double what they're supposed to be.  I think I have thoroughly checked/reheated all of the black wire connections.  So, I think I'm back to stumped...

 

[Paul Birkeland]

Getting 2.9K ad 7/9, then an OL reading, then back to 2.9K still supports the statement that there is a poor solder joint on your ground buss.

 

[Doc B]

It's difficult to tell for sure from the photo but I thought it looked like terminal 3 might need more solder.

 

[larmader]

Ok, this whole thing may have been a red herring.  I believe I was checking the voltages on the AC side of the meter instead of the DC side. I'm not familiar with the symbol it is using to denote the AC or DC side.  So, switching the meter to the _other_ side, whichever that is shows the right voltage levels.  So I went ahead and hooked it up to my DAC and headphones, and it appears to sound great!

I have to apologize for the time wasted.  Thanks to you guys for jumping in, now just shoot me.


Very excited to give this thing a listen!

 

[Paul Birkeland]

No need to apologize, you have well soldered grounds now!!!