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On the TMB channel with boost on and at max volume and gain a loud hiss / scratching / squealing sound occurs as the treble control reaches 9. The position of the mid and bass controls have no affect on the noise. The noise comes on immediately and the noise volume does not increase as the treble control is increased to 10. As soon as the treble control is decreased back below 9 the noise stops. This does not occur when not in the boost mode. It makes no difference whether a guitar is plugged in or not. Any suggestions? Thanks

Try reversing the leads to the plates of the power tubes on the output transformer.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Stephen,

Switched the leads and the noise is gone. The amp is sounding great. Classic tone when paired with a mid-70's 100 watt Marshall cab. Thanks again for a great product and fantastic support.

Bruce

Great to hear the problem is gone. In the end, which tube is the blue one attached to? I'd like to know if the OT polarity on that particular transformer was reversed.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

In the end the blue lead is on V4. Opposite of the schematic.

It's quite uncommon for that polarity to be wrong, but at least it is sorted out.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

This stuff comes up often but usually where there is a feed back loop.. negative becomes positive feedback= oscillator.. but with the 18 what's going on ?