Failed Final Voltage Check (resolved)

[clittlej]

Hey guys,

Like the title says my crack failed the final voltage test. It passed 100% the resistance check however. I've made two quickies and some guitar pedals all with no issue but I'm sort of baffled on what's wrong with this crack. The 9-pin LEDs are not lighting. The heater wiring on both L and R seems fine, both plates (edit: heaters on both sides) of each tube glow normally. Here are the readings.

1: -.794 (should be 50-100)
2: -.796 (should be 170)
3: 0
4: -.8 (should be 170)
5: -.796 (should be 50-100)
6: 0
7: .0056 (should be 90-115)
8: 0
9: .0033 (should be 90-115)
10: 0
 
These decimal places are all in their correct spots. I'm extremely confused. Any help would be greatly appreciated. I'm attaching pics of the wiring. Thanks in advance!

 

[Doc B]

Um, heaters should glow. Plates definitely should not glow.

Sounds like the high voltage is not getting to the tubes. What is your voltage at B2 and B5?

 

[clittlej]

Hey Doc, sorry, I got lazy with my language. I've been troubleshooting this for hours. I didn't mean the actual plates were glowing, I was using "plate" as another word for "side." As in the filaments. The tubes look exactly as they should when the the amp is on.

 

[clittlej]

B2: -.78
B5: -.78

 

[Doc B]

OK, how about DC voltage at terminal 13? And, where are you connecting your black test lead?

 

[clittlej]

13: -.78

The black test lead is connected at 12U.

 

[Doc B]

Might be best to make sure the meter is working correctly before we test anything else. Try measuring a fresh battery with it and see if you get the proper voltage.

 

[clittlej]

I've replaced the batteries in the meter and checked voltage readings on one of my quickies to make sure it's working correctly. All the readings on the quickie were perfect so the meter seems to be functioning fine. Should I redo the solder joints from 11-15 and 18-21? I assume if the voltage isn't getting to the tubes as you said that's where the problem would be. I also did an audio test just to see if there was any output from the headphone jack. There was no sound or noise, just silence.

 

[Doc B]

You need to trace to the point where you lose voltage. Start with your meter set to AC and make sure you have AC voltage at the high voltage secondary output of the power transformer (manual p.29). That is terminals 11 and 12 on the transformer. You should see around 175VAC. If you have that you need to work through power supply, measuring DC voltage at terminals 21, 15 and 13. Also make sure that all of the ground connections are good at terminal 12 and everywhere else in the circuit. We are having a meet today here at Bottlehead, so I may not be able to respond to this thread very often.

 

[clittlej]

Per p. 29, I'm getting 175VAC output from the transformer at 11 and 12.

13: -.787
15: -.794
21: 240V

No worries on not responding that often. Thanks for the help. On the 21 side of the 5W resister lead I'm getting 240V, and on the 15 side of the lead I'm getting -.813V. Could I have fried the resister somehow?

 

[Doc B]

First thing is try resoldering the connections of that resistor. Could just be a cold solder joint. Unplug the amp before you solder.

 

[clittlej]

I resoldered and I'm getting the same readings. The joints are solid. Am I correct in thinking a reading of -.78V on the 15 side of the 5W resistor lead while the 21 side lead has a reading of 240V could mean something is amiss with the resistor?

 

[clittlej]

Update: I replaced the 5W resistor with a new one and now all the voltage readings are perfect. (edit: I must have fried it somehow, and I think I know when it happened. Not trying to say you sent a bad part). Thank you Doc for the help!