Help with troubleshooting

[ajmarshall]

So I built my S.E.X a few years back and had it up and running. Then one of the channels crapped out on me. The right channel seems to be working fine but the left channel output is almost nothing. What does come out of the left channel has no lower frequency sounds. The channel also makes popping sounds on startup and shutdown ( mostly on shutdown). resistance checks come out ok except for terminal 40 which seems to be an open circuit and there is some weird readings on the volume pot. Voltage checks come out ok but again terminal 40 does not read 0 volts. I get inconsistant reading when I check it ( some even negative voltages) but it changes as I take the measurement.

Any help on getting this amp back up and running would be much appreciated.

Andy

[JC]

For starters, have you tried swapping input cables, tubes, etc.?

[ajmarshall]

yup. problem is consistent with different speakers, cables, headphones and when i switch the tubes the problem stays with the same channel

[Grainger49]

Then check the resistances at the end of the manual. If they are OK go on to the voltage checks.

Post those that are more than 15% off the expected reading.  Also, please post the expected reading with those that are too far off the expected.  That keeps us from flipping back and forth through the pages seeing where the voltages are and what is expected and what is connected to the wrong readings.

[JC]

What Grainger said.

And, good for you for checking some of the "easy" stuff already.  I can't count the number of times I wish I would have done that.

[Paul Joppa]

T40 should go to ground through the output transformer primary. There might be a loose connection on one of the transformer wires somewhere.

[ajmarshall]

Checked the wiring to the output transformer looked ok so I chopsticked the solder joints for the OT and didn't notice any change. I could be wrong but if there was a bad connection with the OT I don't think any signal would be passed to the speakers. I am getting sound out of the speaker just no low end. I put a function generator on the input and swept through frequencies to see where it cuts out. It seems like any frequency below 125Hz are not getting the speaker at all, but above that I am at least hearing come out of the speaker.

[Doc B.]

Even though the connections look good, it might be worth reheating the connections to the output transformer to see if anything changes.

[ajmarshall]

Thanks for the input so far. I tried reheating the connections to the OT but problem is still happening. Any other ides people have would be great.

[ajmarshall]

So after reheating a few different solder joints I got this amp back up and running. I wish I knew which one it was because didn't test after reheating each joint but it's working now. Thanks for the input everyone.