Resistance check errors

[Colman]

Hello, I am checking resistance values with the Mainline. I just finished all the soldering and I am up to page 86 of the manual. But I am getting wrong readings where the 10μF 250V film capacitors are connected. At terminal 15 the manual says it should be "210-220 Ohms", but I am reading OL (overlimit or infinity). At terminal 20, the manual says it should be " * ", but I am reading "10.7M Ohms." I get similar readings at terminals 25 and 30, where the other 10μF 250V film capacitor is connected. Also at terminals 19 and 22, the manual says it should be " * ", but I am reading 193k Ohms. I don't think it is a wiring or soldering issue because the readings are consistent for both capacitors. What am I missing? Is it safe to go ahead and check the voltages? Thanks for your advice!

[Paul Birkeland]

Can you report the resistances at terminals 5 and 10 on each output transformer?

[Colman]

For output transformer A, terminal 5 reads 216.3 Ohms and terminal 10 reads 0.1 Ohms. For output transformer C, terminal 5 reads 215.6 Ohms, and terminal 10 reads 0.1 Ohms.

[Paul Birkeland]

Terminal 5 on each OT connects to 15 and 25.  These can't be both connected and not show that improper resistance.

[Colman]

I see I missed a step! From page 85 of the manual, the photo shows a red wire connecting the OTs to 15 and 25. I am now reading about 218 Ohms for both 15 and 25. Terminal 20 now correctly reads OL, and 30 is wandering around in the low MOhms. I am still getting about 193 kOhms at 19 and 22. They are supposed to be “ * “, but since they are greater than 1 Ohm, I suppose it is ok to continue with voltage testing?

[Paul Birkeland]

Yes, I think you're OK to turn that on and perform your voltage checks.

[Colman]

Voltage checks OK. Except terminals at +275VDC and both IAs at AB all measure 242V. I believe that's within the 15% acceptable tolerance. Let me know if it is not though, and may cause issues later! The bias adjusted as they should. My Mainline powered up with no issues. My initial impression of how it sounds is excellent! It has a beefy, energetic sound with nice headroom. The Coarse and Fine Volume controls are handy to have. They tailor the music to suit a person's listening preferences. The release on the ¼" TRS jack is sticky though, but I hope it will loosen up over time. Overall this is a great kit and fun to build! Thank you, Paul, for your help!

[Paul Birkeland]

What is your incoming AC powerline voltage, and how is your power transformer wired?  That 242V is enough for the amp to work, but it would make me wonder a bit about the power transformer wiring, as well as how the solder joints are on the 270 ohm resistor on the power supply board (you can post the DC voltage on each leg of that resistor, which is also somewhat helpful).

[Colman]

My line voltage is 109V, which I think is low. I'm having power issues in my house, which I am looking into. Would that cause the 242VDC?

[Paul Birkeland]

If you have the power transformer wired for 120V, then yes.  You'd want to use the power transformer configuration listed for "Less than 115V" that starts on page 44.  When the power issues are resolved, you can go back to 120V. 

[Colman]

Yes, it is wired for 120V. It's a plan!