Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: toomanyslurpees on November 20, 2011, 10:24:02 pm
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1-I have a pro jr that I ripped the PCB out and did a point to point job on it for the sake of learning. I had it running but not 100% and haven't touched it in over a year, finally got back to it. There was a weird interaction between the volume and tone knob that gave me a squealing in certain tone and volume position. I finally did some poking around and discovered it's because the wires to the output transformer was close to the wire to the tone pot, so I may have made a poor choice of layout but it seems like it if I get the wires separated enough it will be fine. I was wondering if making a small aluminum plate to sit between the pots and the turret board would be benifitial?
2-If the amp runs pretty quiet with no input and the volume dimmed does that mean I've been as successful as I'm going to be in reducing noise in the amp? as in can introducing a signal introduce noise that is being created within the amp instead of just amplifying external noise?
(http://i171.photobucket.com/albums/u305/toomanyslurpees/016-1.jpg)
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That's a nice job on the turret board an wiring, lead dress can make a huge difference, chopsticks are helpful in this process.
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Is it still a Pro Jr? If so, does disconnecting the NFB loop from the speaker jack help?
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You did a super job on the tag board, looks great.
"If the amp runs pretty quiet with no input and the volume dimmed does that mean I've been as successful as I'm going to be ...."
Could be, *provided* you are not using a shorting-type input plug (which you probably ARE). With nothing plugged into the input, if the input to the first preamp is shorted out, that's kind of cheating as far as determining your noise floor.
I think I would want the output tranny leads right up against the chassis.
Other than that, looks very nice.
Did you ever run the amp outside of the chassis (eg; NOT next to the speaker) and experience the same noise/feedback/howl?
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Yep, still a pro jr except there was one cap I was going to put on a switch but I ended leaving it out. the NFB is on that switch near the output. The squealing weirdness changes and goes away when I play with the output transformer wires but I haven't seen if I can get the wires to sit where there's no weirdness because I was begining to drive my roommate nuts, was just wondering if a metal plate could act as a shield between the two.
Actually, I'm not using a shorting jack, I thought it would be a good idea to use the extra tab on the input jack so I could mount the first two resistors on there and save some room on the board, so if there's nothing plugged into the jack it buzzes like crazy, lesson learned.. I guess I should say it's quiet with the volume dimmed and a guitar plugged in with the volume down.
Thanks for the compliments!