Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: punkykatt on December 09, 2015, 06:57:27 pm
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http://el34world.com/charts/Schematics/files/ampeg/Ampeg_GS12R.pdf (http://el34world.com/charts/Schematics/files/ampeg/Ampeg_GS12R.pdf)
Hey Guys, Have a 1966 Ampeg Reverberocket on the bench that has been hacked and modded. Im putting it back to original per schematic. I got everything working except the tremolo. While replacing all the .047 caps in the trem circuit one of the leads going the neon bulb in the roach broke off right at the glass bulb. :cussing: I cut away the heatshrink and installed a NE2 neon bulb with a 22k resister that came attached to one of the leads that I happen to have in stock. (the original bulb did not have a resistor on one of the leads?) I put new heatshrink on and hooked it up. Tremolo works, but when I turn the volume to almost full (75%+) and turn up the intensity almost full, I get this ticking/thud sound. I have the lead dress as short as possible and away from the board. The intensity pot is not far from the trem circuit maybe 4 to 5 inches. All resistors read good. I know there is a mod for the Fender roach for this problem, but this circuit is a bit different. Fliptops website says they have a limited supply of the TM-1 roaches and do not have anymore in stock. Does anyone have any ideas or suggestions to decrease this ticking/thud noise? Any help is much appreciated.
Punky
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Check for DC at the 4Meg Intensity pot legs. If even a tenth-Volt, suspect (replace!) the 0.01u cap before it.
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Thanks PRR, I changed out that .01 cc and it did quiet down the ticking/thud. Its ever so slight with volume and intensity full up. And thats with my hearing aids turned up too. :l2:
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I replaced a failed trem module in an old ampeg gu-12, it ticked until I made sure the outer casing was well-grounded. Not sure if this could be the source of your noise?
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Thanks Thermion, Good to know. This is a roach type module, no casing just heatshrink.
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It is a super-high impedance point. thermion's theory isn't silly. While you did fix the big issue (a leaky cap), wrapping some grounded foil around the roach may help the lower-level crap. (Don't get foil on leads.)
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Where can I get foil I can solder to? I have some copper shield from a dead Egnator PT I dismantled. Perhaps I can make a small clam shell type box with notches for the roach leads to go around the roach. The roach leads already have heat shrink on them. Then ground the box.