getting negative voltages... help?

[Armaegis]

Argh, so I've checked and rechecked all my solder points, cap and diode orientations, have the latest manual corrections, etc. My resistance checks look good, tubes power up and glow, but my voltages make no sense. This is what I've got...

1      -1 (all the -1's are around -0.8)
2      0
3      0  
4      -1
5      0

6    0
7    0
8    0
9    0
10    0

11    0
12    0
13    -1
14    -232
15    -1
16    0

17    0
18    -90
19    -86
20    -232
21    -1
22    0
   
a1    0
a2    0
a3    1
a4    -232
a5    -232
a6    -1
a7    0    
a8    0
a9    -232

b1    -1
b2    -1
b3    0
b4    -1
b5    -1
b6    0
b7    -232
b8    -233


Anyone have a clue where I went wrong? Is it possible I have a bad component somewhere?

 

[Doc B]

OK, somehow you are getting a reading of -232 Volts where you should be seeing 0 volts, and 0 volts where you should be seeing 206 volts. So for some reason it appears that the voltages are shifted relative to ground. It's possible you may have shifted the wire connections on the terminal strips on either side of the power transformer or the front terminal strip. Double check the numbering of the terminals and the wires connected to them. Also, there is a chance your meter is not working properly. It might be worthwhile to borrow another meter.

 

[Armaegis]

Double

 

[Grainger49]

Are you saying that a new look at the voltages in the voltage check gives good readings?  If so, play music.

 

[Armaegis]

No no, I meant the numbering and wiring looks correct. My voltages are still pooched.

edit: I'm kinda tempted to just plug in headphones and see if I hear anything

 

[Grainger49]

You might post a picture.  Have you checked the ground connections?  Doc indicates that there seems to be no ground at one point when he said you have -232V where you should have zero.

 

[Armaegis]

I'll get some images up later. Any particular spots I should snap pictures of?

I'll double check my grounds again... or maybe I'm accidentally grounding somewhere I shouldn't be?

 

[Grainger49]

I think the terminal strips around the power transformer might help Doc see if there is something that an expert can spot.  I don't have a, oops almost said it, I don't have this model.

Measuring resistance from those terminals that should be ground to the ground lug on the IEC connector would be a good check against a floating or lifted ground.  If your meter has ranges set it on the lowest resistance scale.  Then touch the two meter leads together.  This is what zero really will read.  Then check to the IEC connector ground lug.

 

[Armaegis]

Ok... so I have no idea what happened. I randomly tried plugging in one of those $2 airline headphones (using a 260 ohm adapter I made) and lo and behold, music came out. Turned the volume down and checked the voltages, everything matched what the manual except for:
- everything that should be 90 was around 60
- terminal 19 measured 80
- terminal 20 measured zero
- terminal 21 has 210V

Unplugged the headhones and rca cables, voltages still worked out. What the heck? I've shut things off for the night; I wonder if it'll still work tomorrow.

 

[Grainger49]

What is the meter that you are using?  Does it "autorange."  That means you set it on AC or DC volts and it selects the proper range for you. 

It sounds like you have a measurement error here.

 

[Armaegis]

It's just a cheap mastercraft meter, but I know it works since I've used it on other small projects.

Aside from my slightly askew voltages (listed in previous post), my resistors are also running really hot... enough to start melting the wire. The 3k resistors especially so.

I'm also getting some slight graininess to the sound.

 

[Doc B]

The 3K resistors are supposed to run hot. There shouldn't be any wire or anything else touching them. The graininess will probably go away with break-in.

 

[Armaegis]

Hmm, guess I'll have to fiddle with some of the wires and space them out a little. I should have planned for that a little more carefully earlier on.

Any idea why my voltages at 20&21 seem to be flipped?

 

[Doc B]

Any idea why my voltages at 20&21 seem to be flipped?

http://www.bottlehead.com/smf/index.php/topic,657.0.html

 

[Armaegis]

Wow, I checked that thread several times and never even noticed the second post. Well I feel silly now.

Is there any sort of minimum distance that the wires should be from the resistors? Just the way I have things configured right now, I can only get a couple millimeters spacing. Or should I desolder a few things and move wires around (my soldering skills might not be up to that, but who knows).