Final Voltage Check

[Paul Birkeland]

The LED not lighting will also screw up those voltages.  Can you set your meter to measure diodes and measure the LED in both directions?  Also, be sure the connection that ties pins 4 and 5 together is doing its job.  Something is amiss with the 12AU7 socket.

[tdogzthmn]

How can I tell if my multimeter can measure the diodes?  I have both an analogue and digital to use.  I checked connections A4 and A5 and made sure they were attached to the pins.  I took another reading of A8 and got 13.2.  While I was poking around A8 I noticed that the other light LED would sometimes go out.

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[Paul Birkeland]

Resolder A4.  Also add some solder to all of the lower joints on the 9 pin terminal strip. 

[tdogzthmn]

I noticed when checking the voltages of terminals 4U and 5U, when I touch the red lead to the terminal the LED between A3 and the center pin with shut off.  The other LED still has not turned on.  I also when through the instructions once again to be sure the components were installed correctly.  I am still stumped as to why my voltage readings are off.

[ironbut]

It could just be the picture, but the solder joint on the center common ground looks a little iffy (maybe a cold joint?). I know when I'm soldering diodes with short leads, I get nervous about overheating 'em and sometimes pull the iron off the joint too soon.

[Doc B.]

You might try measuring resistance across the LED that doesn't light up ( amp turned off and unplugged for this). Since it is a diode it will conduct in only one direction, and in that direction give a reading with the meter probes measuring from end to end (maybe about 1.5K ohms to 2K ohms if I remember correctly). Then when you swap the probes end for end it will read infinite resistance. If it reads infinite both ways it may be damaged, in which case we can send a replacement. 

[Paul Birkeland]

Yes, the joints on that terminal strip look mostly suspect. When touching them with meter probes causes things to change, the components are not properly soldered.

[Paul Birkeland]

Yes, resolder all of the connections on that terminal strip. When measuring voltages causes intermittent connection issues, there are bad joints.

[dumbo]

I did a resolder on A1 and rechecked the Terminals but did not get any significant changes.  The terminals which have significant readings were: 1 (143.5), 7 (148), 19 (91), 20 (-0.01).

Here are the readings from the tube pins.  Also noted that only the LED on connection A3 was lit, the LED between A8 and the center was not.

A1  74
A2  0.0
A3  1.583
A4  -0.0
A5  -0.0
A6  148*
A7  0.01
A8  0.002*
A9  -0.001

B1  150*
B2  170
B3  149.2*
B4  74.2*
B5  170.2
B6  99.3
B7  -0.001
B8  -0.001

Not sure if you have resolved this or not.  I had similar out of whack readings.  After a couple days of pulling what's left of my hair out, it turned out to be a bad 12AU7 tube.