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Powertube change and Rectifier Q...

11/11/1999 11:39 AM
Lars	Powertube change and Rectifier Q... Yeterday I changed Powertubes in my Marshall Bluesbreaker combo from Groove Tubes 6L6 to Sovtek 5881. I messaured the bias before I switch tubes, it was 28 mA. Something went wrong when I moved the amp and I accidently pushed the rectifier tube (Some Chines GZ34),something come loose inside the tube. I was lucky and found a new one (Ruby Tybes GZ34) at a local store in an hour. After the switch of rectifier tube I messaured the bias (with the old power tubes) and now it was 36 mA and the anod voltage 388V. Why ????????????? I forget to messaure the anod voltage with the old rectifier tube. After the rectifier switch I went back to do what I actually was going to do. I switch the output tubes and set the bias to 32mA, the sound was improved in my opinion more compressed and with an earlyer breakup. I change the feedback resistor from 27Kohm to 78Kohm. First I put a 100Kohm pot instead of the 27 Kohm resistor, played and change the possition of the pot, when I was satisfied I messaured the value, it was 78Kohm. After the feedback change the amp got more distortion and maybe a looser feeling in the lower notes. Lars

11/11/1999 11:39 AM

Lars

Powertube change and Rectifier Q...

Yeterday I changed Powertubes in my Marshall Bluesbreaker combo from Groove Tubes 6L6 to Sovtek 5881. I messaured the bias before I switch tubes, it was 28 mA. Something went wrong when I moved the amp and I accidently pushed the rectifier tube (Some Chines GZ34),something come loose inside the tube. I was lucky and found a new one (Ruby Tybes GZ34) at a local store in an hour. After the switch of rectifier tube I messaured the bias (with the old power tubes) and now it was 36 mA and the anod voltage 388V. Why ?????????????
I forget to messaure the anod voltage with the old rectifier tube.
After the rectifier switch I went back to do what I actually was going to do.
I switch the output tubes and set the bias to 32mA, the sound was improved in my opinion more compressed and with an earlyer breakup. I change the feedback resistor from 27Kohm to 78Kohm. First I put a 100Kohm pot instead of the 27 Kohm resistor, played and change the possition of the pot, when I was satisfied I messaured the value, it was 78Kohm. After the feedback change the amp got more distortion and maybe a looser feeling in the lower notes.

Lars

Replies:

Ken Gilbert Lars, as to your question of why th... -- 11/11/1999 7:35 PM