First off, thanks for any help.
I recently decided to "upgrade" my 5150 II that I purchased new a long time ago. This amp was completely stock. I ordered new JJ high gain tubes (pre and power tubes), and a bias test adapter from a reputable online vendor.
First, I did the bias mod by replacing the 12k ohm resistor with a 6.8k ohm resistor on the bias adjustment circuit board. Next, I replaced the tubes and cleaned the sockets with electrical contact cleaner as I went. Finally, I biased the power tubes to 36 mA using the adapter.
I had a very noticeable cloudy noise in both channels (clean/lead) of the amp even when the guitar volume was turned off. I diagnosed the problem to a pre amp tube that both channel signals travel through. I switched tubes (these tubes were alike) around and got it to not make the cloudy noise anymore. Next, I re-biased and tried it out.
It sounded great for about 30-60 minutes, but then the distortion started to kinda of crackle and then cut out with ~90% drop in volume. I troubleshot some more (not changing anything, but I did try a different cab and had to change the impedance selector on the back of the amp to accommodate), then I tried a different speaker cable and it worked. I played for about 30-60 minutes and the same scenario happened... crackling into volume loss.
The tubes all seem to look fine. My gut says something is up with the impedance selector, but I'm not sure. This just happened and I'm immediately posting here. Any suggestions would be GREATLY appreciated.
I recently decided to "upgrade" my 5150 II that I purchased new a long time ago. This amp was completely stock. I ordered new JJ high gain tubes (pre and power tubes), and a bias test adapter from a reputable online vendor.
First, I did the bias mod by replacing the 12k ohm resistor with a 6.8k ohm resistor on the bias adjustment circuit board. Next, I replaced the tubes and cleaned the sockets with electrical contact cleaner as I went. Finally, I biased the power tubes to 36 mA using the adapter.
I had a very noticeable cloudy noise in both channels (clean/lead) of the amp even when the guitar volume was turned off. I diagnosed the problem to a pre amp tube that both channel signals travel through. I switched tubes (these tubes were alike) around and got it to not make the cloudy noise anymore. Next, I re-biased and tried it out.
It sounded great for about 30-60 minutes, but then the distortion started to kinda of crackle and then cut out with ~90% drop in volume. I troubleshot some more (not changing anything, but I did try a different cab and had to change the impedance selector on the back of the amp to accommodate), then I tried a different speaker cable and it worked. I played for about 30-60 minutes and the same scenario happened... crackling into volume loss.
The tubes all seem to look fine. My gut says something is up with the impedance selector, but I'm not sure. This just happened and I'm immediately posting here. Any suggestions would be GREATLY appreciated.
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