Hello all. Been away from homebrew amp-building and Ampage for 10 years or so.
Playing out with the band constantly during that period left little time for tinkering with the hardware. My old DIY amps served me well for many many shows. Recentlly quit the grind for awhile and decided to build something new. Settled on a fairly stock 5E7-type circuit. Got it built and it sounds great, for the most part. Tested it out using the 4 ohm speaker pair in my Blues Deville. Worked like a charm. Very little noise, decent tone etc. Then I connected it to a single Eminence Screamin' Eagle at 8 Ohms in a sealed cabinet and it immediately started howling at around 300Hz with no input and volume controls at zero. the amp is about 5 feet away from the speaker. Sometimes, it won't howl immediately. Just nudge either volume control though and off it goes. Could be something as simple as lead dress but nudging the wires around aren't making much difference. Can't detect anything overly microphonic either. Interesting case. Back to an 8 ohm paralleled speaker pair this time and all is well. Could the damping effect of parallel speakers keep this beast under control and it loses that with a single speaker? The amp was built using iron from Triode, Chassis from Mojo, and NOS tubes, resistors, sockets and stuff from my antique radio parts inventory. Made the eyelet board an exact replica of Fender's. Wiring is ok. All caps are new mylar and filter caps are new also. Voltages across the board are well within tolerances including bias on the 6L6GCs. B+ is 418 volts from a solid-state rectifier. Any ideas?
Thanks In Advance!
Dave
Playing out with the band constantly during that period left little time for tinkering with the hardware. My old DIY amps served me well for many many shows. Recentlly quit the grind for awhile and decided to build something new. Settled on a fairly stock 5E7-type circuit. Got it built and it sounds great, for the most part. Tested it out using the 4 ohm speaker pair in my Blues Deville. Worked like a charm. Very little noise, decent tone etc. Then I connected it to a single Eminence Screamin' Eagle at 8 Ohms in a sealed cabinet and it immediately started howling at around 300Hz with no input and volume controls at zero. the amp is about 5 feet away from the speaker. Sometimes, it won't howl immediately. Just nudge either volume control though and off it goes. Could be something as simple as lead dress but nudging the wires around aren't making much difference. Can't detect anything overly microphonic either. Interesting case. Back to an 8 ohm paralleled speaker pair this time and all is well. Could the damping effect of parallel speakers keep this beast under control and it loses that with a single speaker? The amp was built using iron from Triode, Chassis from Mojo, and NOS tubes, resistors, sockets and stuff from my antique radio parts inventory. Made the eyelet board an exact replica of Fender's. Wiring is ok. All caps are new mylar and filter caps are new also. Voltages across the board are well within tolerances including bias on the 6L6GCs. B+ is 418 volts from a solid-state rectifier. Any ideas?
Thanks In Advance!
Dave
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