Voltage checks wrong [resolved]

[tintin]

Just finished putting all the components onto the board, done and passed all the resistance checks, powered on but DC voltage checks all display 0, and the LEDs do not light. I have retouched all the solder points on the board and checked for connectivity, all seem to be ok.  I have redone the initial AC voltage testing off of points 11/12 and 7/9 on the transformer, both within range although slightly lower readings than when I did it the first time at the start of the manual. Both tubes glow.

Where would be a good place to start looking for suspects? I am suspecting the 12AU7, it seems to not be glowing as strong as it was on my initial glow test but may be placebo. I unfortunately don't have any other 12AU7s or another amp that takes it to try it. Any help on the circuitry is much appreciated!

And if it makes any difference, my AC source voltage is 248V. Will provide pictures of any necessary sections.

 

[Paul Birkeland]

I would start by using your meter to measure the voltage of a 9V battery, just to be certain that the issue isn't using the meter itself.

The red wire going to A7 needs to be pushed in more.  If all that exposed wire starts touching other terminals, you will make tons of problems.

I don't see anything obvious from your build photo that would prevent the power supply from developing high voltage.  This issue is not the 12AU7.  You could pull all the tubes out of the amp and there would still be measurable high voltage present while it's running.  The fact that the LEDs don't glow but the tubes still do does suggest that there is an issue in your build.  It's really, really, really important not to focus on the LEDs as the cause of your problems.  Oftentimes there is something else that's not quite right which prevents the LEDs from illuminating, so I would suggest leaving them alone for now until you can get some reliable DC voltage measurements. 

Lastly, I would go through and reflow every solder joint in the amp.  It will take you 15-20 minutes, and you could add a little solder to each joint and a lot more heat.  This is what I do for all the flat rate repair Cracks that I receive, and it fixes the vast majority of them. 

 

[tintin]

Thanks for the reply Paul. Went through and soldered everything through again, resistance checked again, but still no luck. Is there some way I can follow the path to measure some DC voltage earlier in the chain before terminals 1-10 to see where it drops, would that help? Not too sure which terminals to measure if so. Thanks!

 

[tintin]

Edit; went through the circuit starting from terminals 12 checking resistance, found 2 points that weren't quite right between terminals 12 and 13. Looks like the 270ohm resistor wasn't quite wired right from behind even though it looked ok from the lateral side. Tough spot to get into with solder!

All fixed up now and perfect voltage checks. Time to listen. Thanks Paul for your help

 

[Paul Birkeland]

I'm glad you found the problem so quickly.