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Amp/Preamp Asylum Looking for a new Amp or Preamp? If you're after tubes, post over here. |
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Amp/Preamp Asylum Looking for a new Amp or Preamp? If you're after tubes, post over here. |
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In Reply to: Out for Delivery - Tube Amp posted by creativepart on June 20, 2019 at 08:58:08:
I'm posting this for other users that encounter the same issue I did when I switched to EL34 power tubes.
The CM2 comes with KT120 tubes. The fellow I purchased my used amp from told me that he had used the amp with EL34 tubes most of the time he owned the amplifier. Looking online I saw plenty of praise for EL34s in the CM2, so I ordered a quartet of the new Russian "Mullard" EL34s.
After swapping the 120s for the EL34s I went to bias the new tubes. To my surprise the biasing meter showed zero mA current for each tube. I turned the bias adjustment pot a couple of turns each direction and nothing. I called Rogue Audio but it was too late in the day. A search of the web was turning up nothing, but I finally found someone else posted on this topic AND most importantly, the solution.
You have to turn the bias adjustment pot - counterclockwise - for between 8 and 12 revolutions before the meter starts to indicate the bias current setting for the new tubes.
According to internet posters some say the tubes should be biased to 30mA OR 34mA depending on who you listen to. I sent mine at 32mA to split the difference.
Hopefully, this post will help others searching for a reason that their new tubes show up as 0mA on the Cronus Magnum bias meter.
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Biasing EL34 Tubes on Rogue Cronus Magnum II - creativepart 10:11:08 06/28/19 (0)
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