Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: proaudioguy on February 17, 2024, 02:23:48 pm
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I wish I hadn’t. This Pro Jr kit is just bad. I had everything “right” the first time. I have tweaked, probed, measured every resister and cap as it was going in and 3 times since. Traced every wire. I redid the entire grounding scheme. This thing cannot, NOT buzz. I replaced the bridge rectifier with 4 UF4007 Diodes and placed snubbers across them just like the Pro Jr 4 has. No joy. I bought an osciliscape. The power at the first cap filter looks like this photo (oh and that cap was a 47µF, I put in a 100µF trying to solve this, before I bought the scope). Now its getting flattened out after the other 2 caps but this noise is still IN everything. The original Pro Jr (circa 1993) that was in this chassis did not do this. I should have not sold the circuit board and should have just put it back in here but its too late for that.
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Without going back and looking at your previous threads, its pretty hard to figure out what you are asking about. That's likely why you have no replies.
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This Pro Jr kit is just bad
What "kit" are you referring to?
With respect, Tubenit
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Replace the PT.
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Replace the PT.
I was about to say..
When you have noise that's this insidious, you need to consider the possibility that it's electrostatic noise being coupled in via the PT due to poor design, defect, or just a lack of shielding in a noisy environment.
If possible, take the amp to another location - different circuit, another home, your job, etc and see if it's still as noisy.
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Sounds like your transformers are coupling or your power valves are out of balance or one is out. Don't discount your phase inverter either. Check current on both valves and/or replace. Move the output transformer and see if there's a difference.
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Your schematic and good pictures of your wiring would be helpful.
So, this is the same transformer set that was ok before?
Also, where are your diodes mounted?
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This Pro Jr kit is just bad
What "kit" are you referring to?
With respect, Tubenit
He is probably talking about my Pro Jr boardsWith 100's of them out there over many years working perfectly, it's amazing that he thinks it's the boards and not him.