Ceriatone Forum

So, just for fun i thought i would add the ability to run both fixed and cathode bias as described here---->http://www.londonpower.com/cath-fix.htm

My question is this. Is it better to have a shared resistor and capacitor for both tubes or is better to have an individual resistor and capacitor for each tube?

Well if you have shared bias network your tubes have to be matched... with independent bias network, you can use what ever and set the bias individually.... so I would say more flexibility with the second option.

Cool link, Plasticvonaband!  8)

Thanks for the replies, guys. I have been thinking about doing this since i ordered the amp. I actually considered asking Nik to do it for me, but he was already doing alot of mods to the amp as it was, and he was kinda swamped :)

I originally thought about having it switchable to cathode bias to compliment the sound in Sag mode, when i have the Sag resistor engaged to simulate having a tube rectifier, (which works very well, by the way) to make the amp respond completely differently when i wanted to, kinda like having 2 amps in one.

Now I have a second reason. When the Sag resistoe is engaged, the current draw at the cathodes dropd about 10 ma, so, in other words, if I have the amp running at standard voltage, and have the tubes biased to about 40ma, and flip the Sag in, the current drops to 30 ma, way too cold. Of course, rebiasing is not a big deal, but if you are gigging, stopping to adjust the bias can be a pain. I figure if i have the option to go cathode bias at the flip of a switch, i can switch to sag mode and cathode bias, and voila, everything should be fine. Of course, the amp would sound completely different and not very D-Like, but that's kinda the point. I also plan on having the bypass cap able to be switched out, or just elminate it all together. What do you guys/gals think?

I'm about to order (money arrived) and I'm REALLY CURIOUS about the viability of this mod... It would be REALLY useful for me.

I need to know what people think about this BEFORE I order.

WooHoo!!! I'm ordering soon!!!

I don't think that it is a mod that Nik would do, it wouldn't hurt to ask, but i doubt it. I can tell you that the Bluesmaster, the way it comes is simply awesome. I think I can safely say the same about the rest of the OTS series, or any of Nik's amps for that matter. I am simply trying to make the amp more versatile because 1) i can't afford to buy another amp at the moment and 2) even if i could, i don't like carrying two around :) Right now I carry My Bluesmaster 2x12 combo, and my Ampeg Jet II, which has to be mic'd up, of course. I'm still debating on whether or not to do it, but i probably will, or i will have my tech do it, most likely, and i will let ya'll know.

Does anyone have an opinion on whether or not to eliminate the bypass capacitor from the circuit? The reason i am even considering eliminating it is that it would provide the most drastic difference between the tight d-style fixed bias sound, and a more round, mellow cathode bias sound. Any opinions?

Although I also wondered about getting a Cathode biased Dumble style amp, in my case looking to get a more compressed sound, bear in mind that the Fuchs ODS30 I had did not have any compression artefacts - very clean - it sounded cleaner than an OTS, a very refined D-style, and it was cathode biased (you could use 2 x 6L6 or 4 x 6V6)

The amp was good enough that a guy who had owned and rejected an OTS took this off my hands with glee.
Personally I think the BM50 is better than the Fuchs for that type of sound, but personal taste is personal

I have other cathode biased 6L6 and 6v6 amps with amazing compression - 5E3 and Double 5X3-based designs  (much more compression than a DC30), so I assume you can design how much linearity you want

Very cool and encouraging! Once i get over being sick i will have to drop the chassis again and take a look and see how difficult it would be for me to do. Most likely i will take it to the tech, though. I know just enough to mess an amp  up  ;D