18Watt.com

Hello,

I need your help on troubleshooting this amp. OT is a 125C Hammond. I wired OT lug no 2 to positive and 4 to ground to achieve 22.5K secondary. It worked great for a while. today I changed the wiring of the OT, used 1 and 5 to ground. I did not work and instead made a low buzzing noise. I swapped the two wires to original but the amp is not working now!

Please advise what could have gone wrong in this and how to start trouble shooting. this is my 4th amp build

Thank you.

I would check to be sure the amp has B+ on the output anodes. Then check the transformer for continuity on the primary and secondary windings, and confirm it doesn't have a primary-to-secondary short.

Jack

Okay. The output tube is a 12au7. I will check for B+ voltage in its pins.

For contnuity check in OT does the amp needs to be on or off?

Thanks

By all means, turn the amp off. Also disconnect the speaker. If these tests don't point to the problem, it's anyone's guess as to what happened and probably not related to switching the transformer connections. Sometimes, something else happens in the process that gets overlooked. Good luck with it!

power tube has 320 V DC. amp turned off, spkr jack off from the cab and then I did a continuity test from the OT's primary to secondary, it beeps for about 3/4 seconds and stops. is my OT fried?

You did not make the measurement with 320V still on the tube, right? And when you say "spkr jack off from the cab," do you mean the secondary is lifted from ground? There should not be continuity between the primary and secondary windings.