Greetings. I have a question.
I just finished up an ST 70 build. All new. Dynaco A470/PA060 new from Kevin at Dynakitparts. The only mods I’ve done is the Dynakit 80/40/30/20 uf can cap, Dan Joffe’s Stereo 70 Bias Power Supply Upgrade, the yellow sheet mod, and a Triode EF86 board. Running 6CA7 power tubes which are biased a bit on the cool side. I put the amp in service with two other ST-70s and ran it for the past five weeks. I believe it’s got about 60-70 hours on it so far. The amp worked flawlessly and sounded amazing until yesterday.
I now have a crackling “scratchy” sound from the left channel. It sounds almost like a dirty potentiometer on a guitar amp being turned, or a scratchy record being played. It’s constant, but seems to wax and wane in intensity every 5 seconds or so (at idle with no inputs connected.) I have eliminated tubes, the transformer post connectors (Everything seems to be soldered on well to the back of the posts) speakers and cables.
At idle, the sound can be heard from the left channel, when no inputs are connected to the amp, the only thing being connected are the speakers on the 8ohm taps. I’ve done a visual inspection on the output transformer wiring, and everything seems to be neat and tidy.
I was wondering if someone can point me in the right direction. I’m pretty handy with the multimeter, but I don’t have an oscilloscope.
I just finished up an ST 70 build. All new. Dynaco A470/PA060 new from Kevin at Dynakitparts. The only mods I’ve done is the Dynakit 80/40/30/20 uf can cap, Dan Joffe’s Stereo 70 Bias Power Supply Upgrade, the yellow sheet mod, and a Triode EF86 board. Running 6CA7 power tubes which are biased a bit on the cool side. I put the amp in service with two other ST-70s and ran it for the past five weeks. I believe it’s got about 60-70 hours on it so far. The amp worked flawlessly and sounded amazing until yesterday.
I now have a crackling “scratchy” sound from the left channel. It sounds almost like a dirty potentiometer on a guitar amp being turned, or a scratchy record being played. It’s constant, but seems to wax and wane in intensity every 5 seconds or so (at idle with no inputs connected.) I have eliminated tubes, the transformer post connectors (Everything seems to be soldered on well to the back of the posts) speakers and cables.
At idle, the sound can be heard from the left channel, when no inputs are connected to the amp, the only thing being connected are the speakers on the 8ohm taps. I’ve done a visual inspection on the output transformer wiring, and everything seems to be neat and tidy.
I was wondering if someone can point me in the right direction. I’m pretty handy with the multimeter, but I don’t have an oscilloscope.
