rockabilly69 Posted January 8, 2014 Share Posted January 8, 2014 A little tone report. The amp sounds real good but , as I do with most early Ampegs, I decided to tweak the negative feedback resistor. I went from the stock 10k ohms to 76k ohms. This changes the "feel" of the amp and gives it some much needed "crunch; at a lower volume setting. I've tried it with blackface Fenders and found I prefer the stock values. The early Ampegs were made to stay as clean as possible for their wattage range. This little mod moves the amp into more of a Fender tweed sound but tighter, more focused and full sounding than a tweed Deluxe. More to come! Sounds like a great slide guitar amp! Link to comment Share on other sites More sharing options...
slider313 Posted January 10, 2014 Author Share Posted January 10, 2014 The power supply "twistlock" cap can is in. The amp is much tighter and there's no more "fizzle" on the high notes. I had to re-think the value of the negative feedback resistor as the amp was giving it up a bit too early and needed slightly more clean headroom. I also installed a shorting jack on the second channel input. Ampeg's all have a bit of "floor noise" due to the grounding scheme, which runs everything back to the cap can. I split the power supply and preamp grounding and it's almost as quiet as a church mouse. This one is now gig ready and sounds better than I had hoped. Link to comment Share on other sites More sharing options...
Spectrum13 Posted January 10, 2014 Share Posted January 10, 2014 The power supply "twistlock" cap can is in. The amp is much tighter and there's no more "fizzle" on the high notes. I had to re-think the value of the negative feedback resistor as the amp was giving it up a bit too early and needed slightly more clean headroom. I also installed a shorting jack on the second channel input. Ampeg's all have a bit of "floor noise" due to the grounding scheme, which runs everything back to the cap can. I split the power supply and preamp grounding and it's almost as quiet as a church mouse. This one is now gig ready and sounds better than I had hoped. Question: My 65 RRocket II has the original Twistlock cap. (purchased new) if the high notes do not "fizzle", leave it be? How can I tell if the grounding issue was rendered? Last serviced about five years ago replaced two prong plug and some caps.... Link to comment Share on other sites More sharing options...
peterbright Posted January 10, 2014 Share Posted January 10, 2014 that's a great find...play her well Link to comment Share on other sites More sharing options...
slider313 Posted January 11, 2014 Author Share Posted January 11, 2014 Question: My 65 RRocket II has the original Twistlock cap. (purchased new) if the high notes do not "fizzle", leave it be? How can I tell if the grounding issue was rendered? Last serviced about five years ago replaced two prong plug and some caps.... A few symptoms of failing power supply caps are; loud hum, loss of bass response/tightness, "ghost" notes after the note played, a "fizzle" along with the notes played. With preamp electrolytics, or cathode bypass caps, you can get "motorboating" or loss or noise from your reverb. Link to comment Share on other sites More sharing options...
slider313 Posted January 12, 2014 Author Share Posted January 12, 2014 Link to comment Share on other sites More sharing options...
Spectrum13 Posted January 13, 2014 Share Posted January 13, 2014 You went blue. Ready for another 52 years of service? Link to comment Share on other sites More sharing options...
Billgelder Posted January 13, 2014 Share Posted January 13, 2014 A few symptoms of failing power supply caps are; loud hum, loss of bass response/tightness, "ghost" notes after the note played, a "fizzle" along with the notes played. With preamp electrolytics, or cathode bypass caps, you can get "motorboating" or loss or noise from your reverb. "motorboating"? sorry I had to ask. Link to comment Share on other sites More sharing options...
slider313 Posted January 13, 2014 Author Share Posted January 13, 2014 "motorboating"? sorry I had to ask. Yes, the sound it produces can sound like the "sputter" of a motor boat. The bad or shorted cathode bypass cap will let the preamp tube amplify the imperfection in the cap and that's one of the sounds it can produce. Link to comment Share on other sites More sharing options...
Billgelder Posted January 13, 2014 Share Posted January 13, 2014 Got it, Sorry I was thinking of something else. Link to comment Share on other sites More sharing options...
slider313 Posted January 18, 2014 Author Share Posted January 18, 2014 Well, I took the Mercury to band practice last night and, after about 30 minutes, the preamp tubes became very microphonic and it seemed like the whole chassis was affected. Back to the bench today. I changed the input wires to shielded cable and replaced a microphonic wire off the phase inverter. I played it for over an hour with no issues. Link to comment Share on other sites More sharing options...
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