Resistance Issue in Ground Path

[SpeedyDad]

I finished wiring and assembling the Crack but wonder about some failed 0 Ohm readings in the ground path.

First, transformer voltages, glow test, and the resistances to terminals 7, 9, B3, B6, and RCA center pins all checked out. But I have issues where need a 0 Ohm resistance.

The leads of my DMM have a resistance of .6 Ohms, which I take as my baseline. Clipping one lead to U12, I get .6 Ohms readings at terminals 3, 6, 10, 14, 20 and the RCA ground. I get readings of 3-20 Ohms (measurements vary and are not consistent) on terminals 8, 22, 17, 16, 11, the ground tab, the screws that hold the transformer, the chassis. If I set my DMM to continuity, I do get beeps throughout.

If I clip the black lead to the ground tab and then measure the resistance to terminals 22, 17, 16, 11, 8, the chassis, or the screws holding the transformer I get .6 Ohms readings.

It seems that each individual ground path (black wire and chassis) are fine by themselves but don't seem to connect the way they are supposed to (0 Ohm instead of 3-20) Ohms. Where do they actually connect?

Although I seem to have continuity, I resisted the urge to put in the tubes and continue with voltage checks. Any thoughts?

[Paul Birkeland]

The leads of my DMM have a resistance of .6 Ohms, which I take as my baseline. Clipping one lead to U12, I get .6 Ohms readings at terminals 3, 6, 10, 14, 20 and the RCA ground.

Good.

I get readings of 3-20 Ohms (measurements vary and are not consistent) on terminals 8, 22, 17, 16, 11, the ground tab, the screws that hold the transformer, the chassis.

You may be reading some resistance through the chassis plate, which is OK.  Tightening the screw on the front 5 lug terminal strip, the ground screw, and the transformer screws might be helpful.

It seems that each individual ground path (black wire and chassis) are fine by themselves but don't seem to connect the way they are supposed to (0 Ohm instead of 3-20) Ohms. Where do they actually connect?

The electrical ground (black wires) connect to the chassis at terminal 3 through the terminal strip.  The power transformer cover is grounded through the safety ground back by the IEC power entry module.  Seeing a little bit of extra resistance between those terminals and terminal 12 isn't that surprising, but I'd still tighten the hardware to be sure.

Although I seem to have continuity, I resisted the urge to put in the tubes and continue with voltage checks. Any thoughts?

I would double check the black wires at the headphone jack.  The hole is rather large and hard to reach, and we frequently find kits where only one of the wires passing through there is soldered, which can give some unusual readings in the resistance and voltage checks.  If that joint looks good and the hardware is nice and tight, I'd go ahead and check your voltages.

-PB

[SpeedyDad]

Excellent, thanks so much for the prompt help!

It was exactly that screw at terminal 3 that wasn't very tight. That might explain the fluctuating resistance because I checked wires and connections and probably touched that strip multiple times, changing the resistance ever so slightly. I guess I was a little too careful when I installed the sockets. So, I tightened them all, and all values were great. Interesting that after all that careful soldering, counting turns per inch, braiding with love, and double checking all joints it was such a simple thing after all.

Headphone jack wires were all tight and good.

Voltages were all within range. I got readings of a fraction of a Volt where I was supposed to read 0 but I felt that's probably within tolerance. Now, there was nothing that kept me from popping in my first SACD (if you care, Bach Collegium Japan, Cantata BWV 140, Wachte auf, ruft uns die Stimme), and what a great wake up it was. The background is so super quiet, and everything sounds crisp and detailed.

I need to finish the wood and will do some minor modding (a different pot, a choke, and a bypass cap) but feel this is an excellent amp as is. I will share the result when I am done.

[Paul Joppa]

Re:  "...after all that careful soldering, counting turns per inch, braiding with love, and double checking all joints it was such a simple thing after all."

For what it's worth, in my experience (I've been making audio electronics since about 1954) it's almost always something simple like that. The only thing that's NOT simple is figuring out which simple thing is the problem!

[Doc B.]

I've been making audio electronics since about 1954

I didn't know they had invented electricity by then.