Resistance Check Confusion

[Demsy]

Just finished the first amp and did the resistance check. All points are correct except for the B2 and B9 values.

According to the manual B9 should read *, but what I got is close to 0.2 Ohm. I'm using the Fluke 12, when the leads are shorted, it would read 0.1 Ohm. So this means that the actual value is 0.1 Ohm only. Measuring between B1 and B9 gives 0.4 Ohm. I measured on the other unfinished amp's transformator, it also reads 0.4 Ohm and 0.2 Ohm on each leg. So logically the values are the same, but I'm a bit reluctant as the value/s are very close to zero/short.

B2 reads 9.9 kOhm, it should be 8.2 kOhm. But I measured the same value on the other regulator board which is not installed, yet. This is off by around 20%, manual mentioned 15% max.

PJ, Doc, Grainger and other experienced guys, what do you think? Does it look okay and safe to be connected to the power line? I want to be sure before making any further steps, especially powering it up.

[Paul Birkeland]

Hello Demsy,

The B1/B9 readings look good, I wouldn't worry about those. They will be pretty low since there's a small transformer winding feeding B1 and B9, with the center tap of that winding grounded.  With a tube in the socket, the resistance between B1 and B9 will be even lower, and the restistance of the wire in the leads coming from your meter will start to be significant at that point.   


B2 is affected by the little blue trim pot, you can feel free to adjust it until you get the desired resistance before you fire the amp up. 

-PB

[Demsy]

Hello Paul,

Thanks for your explanation! Now I can start finishing the second amp with peaceful mind . I will adjust the trimpot to get the expected value on the B2.

Have a nice weekend!