Reversed OT Primary Leads

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FourT6and2
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Reversed OT Primary Leads

Postby FourT6and2 » Tue May 30, 2017 9:00 am

When building an amp, how do you know which OT primary to connect to which half of the power tube string? I know if you get them reversed it can lead to instant red-platting and oscillation/squeal. So, how do you know if you've wired them reversed or not before you turn the amp on? Let's assume the OT is not a standardized or historic recreation where you can just use the lead colors.

danman
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Re: Reversed OT Primary Leads

Postby danman » Tue May 30, 2017 7:33 pm

In some cases the OT used will have colors that match the original schematic/layout. This still does not guarantee correct orientation though. If you are building a circuit with nfb, it is always wise to leave some slack in the primary wires in case you need to reverse them. If your circuit does not use nfb, it does not matter which wire goes to which side.

FourT6and2
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Re: Reversed OT Primary Leads

Postby FourT6and2 » Wed May 31, 2017 8:48 am

Interesting. So really... there's no way to know which one goes where? You just have to try it and hope you got it right on the first try?

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wdelaney72
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Re: Reversed OT Primary Leads

Postby wdelaney72 » Fri Jun 09, 2017 4:49 pm

This has happened to my multiple times. for EL34 tubes, no red-plating, but that siren sound is crazy loud and fortunately tells you right away that they are reversed.

This also happened to me with KT66 tubes....the tubes didn't red plate, but they did spark internally after a few attempts damaged the tubes. this sucks, since KT66 are definitely more expensive.

I dot know of a way to measure / test before firing up the amp If someone knows, this would be good info to share.
Walter

"There's no great thing in being a soloist. I think the hardest thing is to play together with a lot of people, and do it right." - Angus Young, 1984


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