R
russellconner
Member
Alright, I finally got around to retubing the power section. I put in a new quad of JJ E34Ls from Eurotubes. I also purchased one of their $25 bias probe/adapters, which worked great by the way.
I just wanted to let you guys know what my final settings were, and make sure I set it up properly. My goal is to get maximum headroom from the power section, and use the preamp for distortion.
With the new tubes in place, I measured the plate voltage and found it would start at about 498 VDC at power-up, and stabilize at about 493 VDC after a few minutes. I then used 25W, 70% dissipation, and 493 VDC to calculate a bias target of 35.5 mA. I dialed in the bias current, and left it a range of 33 mA to 34 mA for the four tubes. I only had one scary moment (when testing after setting bias), and found out it was the Tung-Sol in V1 going microphonic and dropping out.
Now, Bogner recommends a lower setting of 22 mA to 28 mA, and some of the guys here in RT prefer a lower setting as well. I'm curious what the differences in sound are with the lower setting versus how mine is set at ~33 mA.
- Will the lower bias setting give the amp more headroom/less breakup?
- How do the two settings differ in their effect on controlling the low end (amount/tightness)?
- (For the hot channel) With the gain at 2:00 and the channel volume at 11:00, where on the master volume should I expect the power tubes to start breaking up?
I haven't pushed the new tubes very hard yet, but intend to give them a good run tonight after work. I'm hoping to see increased headroom and punch with the switch to E34Ls. Already I can tell a huge difference compared to the old tubes, but they were really wore out.
Thanks in advance for your insight/input.
-russell
I just wanted to let you guys know what my final settings were, and make sure I set it up properly. My goal is to get maximum headroom from the power section, and use the preamp for distortion.
With the new tubes in place, I measured the plate voltage and found it would start at about 498 VDC at power-up, and stabilize at about 493 VDC after a few minutes. I then used 25W, 70% dissipation, and 493 VDC to calculate a bias target of 35.5 mA. I dialed in the bias current, and left it a range of 33 mA to 34 mA for the four tubes. I only had one scary moment (when testing after setting bias), and found out it was the Tung-Sol in V1 going microphonic and dropping out.
Now, Bogner recommends a lower setting of 22 mA to 28 mA, and some of the guys here in RT prefer a lower setting as well. I'm curious what the differences in sound are with the lower setting versus how mine is set at ~33 mA.
- Will the lower bias setting give the amp more headroom/less breakup?
- How do the two settings differ in their effect on controlling the low end (amount/tightness)?
- (For the hot channel) With the gain at 2:00 and the channel volume at 11:00, where on the master volume should I expect the power tubes to start breaking up?
I haven't pushed the new tubes very hard yet, but intend to give them a good run tonight after work. I'm hoping to see increased headroom and punch with the switch to E34Ls. Already I can tell a huge difference compared to the old tubes, but they were really wore out.
Thanks in advance for your insight/input.
-russell
