a '46 Rock'ola project needs your help - New York, New England area, 120Hz hum.

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Please understand. There is great advice to be given from all of you, but this project needs to be seen by someone else, and in person. 4 months into a paying project and the customer deserves this amp already.

I ask for someone in New York or New England to spend some time with me and look at this amp in person. THIS AMP HAS BEEN MODIFIED.

Issue: 120Hz hum on the output. Typical values of 70-85mVpp at the speaker. When the Bax TS is disconnected, the value drops by 50mVpp.

Goal: Less than 25-30mVpp hum at output. The treble control produces a ringing above the 70% point in the pot range, if we could fix this at the same time it would be even better.


Please respond ASAP. Thank You very much.
 
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Thank You John, I appreciate your help,

but everyone should also know that:
1. Every component is NEW except for the PT and OT, and the rect. tube. Also excluded here are the input/output terminal connections, as they are still original.
2. Class AB output section.
3. 6j5>Bax TS>12ax7 gain +inversion stages>12au7 driver stage>6l6 output stage

4. All original values of capacitance have been modified to the best of my ability. This means that the original 15uf C1 after the rect. has been replaced with 40uf - the suggested max. capacitance for this style of rectifying tube. Then, RC calculations have been performed to ensure that no resonance occurs in the PS above 50Hz. (5Hz would be the -3dB freq. for these calculations).
5. Original tube VI relationships have been preserved from the original schematic for the 6j5 and 6l6 tubes. The ax7/au7 addition has been created from an online schematic which I will post in a following message.
6. Signal leads are made of a quality Belden shielded cable. There is a long stretch (+/- 8") of B+ line that connects the 6j5 to the TS, and this cable is non-shielded. The plate resistor for the 6j5 is as close to the TS side as possible.
 
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