Spark during voltage check

[Utopia]

New member here! I finished my Bottlehead crack build yesterday, and did the resistance check, and every value was spot on. It's been a slow, careful build, and I was starting to feel confident I would get it right. Then today I began to do the voltage check. I powered up the amp, the tubes started glowing, and the LEDs were shining. Then I tried to measure terminal 1, and got nothing - no reaction at all from the multimeter, not even a zero.

I was using a new multimeter for the voltage measurements, so I thought I was doing something wrong with it. I re-read the DMM manual,  and moved one of the test leads on the DMM. This was the wrong thing to do - I moved it to where it should be for DC current, not DC voltage (in a hurry, in my rubber-sole shoes, left hand in my pocket, weary wife watching..) - then moved on to measure terminal 2, and got a bright bluewhite spark!

Did I break something with that bad measurement?

Thinking back, I'm not 100 % certain the smaller tube was glowing. It wasn't easy to see, up-side-down, and it might have been reflections from the larger tube.

What do I do next?

[Doc B.]

The current setting has a shunt element that makes essentially a dead short thru the meter. That is why you saw a spark. Just set your meter back to read DC Volts and measure again.

[Utopia]

Thanks! That's great to hear 

I realize now also that my initial bad reading was just another erroneous handling of the new DMM by me.

After weeks of meticulous building I finally got to eager to get to listen to this thing!

[John EH]

Thanks! That's great to hear 

I realize now also that my initial bad reading was just another erroneous handling of the new DMM by me.

After weeks of meticulous building I finally got to eager to get to listen to this thing!

Your voltage measurements are to chassis ground.  If your new meter has a clip on lead, take your black lead, put a clip on it and then attach it to the chassis or some ground point on the Crack Amp.  Then instead of having to fool with two leads, two hands you only have to worry about one.  Much steadier and more reliable method of measuring.

John

[Grainger49]

I'm a firm believer that if you are not handy with a meter and need a current reading you should fill up the current input.  It will too easily get you in trouble.

[Utopia]

Thanks for the feedback!

I re-did the voltage check in peace and quiet and all the values were fine. My 90 V readings were down around 78, but all the other ones were within +/- 3 V. During the final measurement on the headphone output the voltage climbed to about 4 V before dropping quickly. So, time to connect it to my Concero DAC and T1s and listen to some music 

[Paul Birkeland]

78V instead of 90V just indicates a 12AU7 with a little extra potency, nothing to worry about.

-PB