Bottlehead Crack Speedball Voltage Problems

[Jake1]

I completed the build and all resistances/voltages checked out and things were working fine for a few weeks.  I turned off the amp earlier in the day and came back to turn it on later but the tubes weren't lighting up.  I checked the voltage at the power input which read 120V but no LED were coming on either speedball board or on the 9 pin tube.  I checked the voltages for the small/large board and they were messed up:

small board:
OA - 226V
1A - 226V
B-A/B - 0V
1B - 226V
OB - 226V

large board:
OB - 1V
G - 0V
B+ - 180V
OA - 1V

Please let me know if you have any ideas.

 

[Tom-s]

Check and double check your heater wiring. The voltages you got are in line with the tubes not heating.
Once that's working, recheck your voltages.

 

[Jake1]

Great advice that fixed it thank you!  I crimped a heater wire but never soldered it so when it was working it was just the crimp holding it not any solder so it must have just shifted slightly since i first built it.  Soldered that joint and all back to normal.

Is there a guide somewhere for what incorrect voltages indicate?  It's interesting you can just tell areas to look at based on which voltages are off and by how much, I'd be interested in looking into understanding that more.

 

[Doc B]

Is there a guide somewhere for what incorrect voltages indicate?  It's interesting you can just tell areas to look at based on which voltages are off and by how much, I'd be interested in looking into understanding that more.

The way you learn that skill is to be a technician for a few years. Basically you look at a schematic for the device, or perhaps you can suss out how the design works by looking at it. Then you figure out what a voltage would change to if some part in the circuit was not connected properly or was shorted, and work from there.

For example, if the LEDs in the basic Crack blow (go open circuit), the tube does not conduct. So the plate voltage on the tube will go high. If you know the plates are pins 1 and 6, you know those are the pins that will read too high if the LEDs blow and go open circuit. Bear in mind that not properly soldering the LEDs could cause the same issue even if the LEDs are good. These are the details that you learn with experience.

Another example would be that you see a very low voltage at the + terminal of the electrolytic capacitors. That tells you that something downstream of them in the circuit is shorted and pulling so much current that it is loading the power supply down. So you look for wires that are shorted out to the chassis or the wrong terminal, or components that may have shorted internally (usually indicated by them looking very cooked).