Rca BC-2B with a 12at7 or 12ax7 for more gain

[mrtnasty]

Anyone ever tried this? Too much distortion?

 

[emrr]

Tube gains on paper are based on infinite loads, as soon as you put them in real world circuits there’s very little gain difference. Especially with NFB present. Wire it up, try it.

 

[mrtnasty]

Tube gains on paper are based on infinite loads, as soon as you put them in real world circuits there’s very little gain difference. Especially with NFB present. Wire it up, try it.

Thank you, I will try it and report back once I get around to replacing the caps and wiring it up.

 

[ruffrecords]

The preamps in the RCA BC-2B have gain fixed by negative feedback. Changing to a 12AX7 will therefore not change the gain. The bias point will be completely wrong and there will probably be insufficient current in the output stage. Drive capability will be compromised, possibly severely, leading to early onset clipping.

Cheers

Ian

 

[k brown]

Maybe better to add gain from different trafo ratio(s)?

 

[ruffrecords]

Maybe better to add gain from different trafo ratio(s)?

The spec for this mixer says the maximum mic gain available is 108dB. If anything I would think these days you would want to be reducing the gain rather than increasing it.

Cheers

Ian

 

[emrr]

It’s a weird one to consider changing. I detailed the NFB gain mod options elsewhere, for an original console or pre. If it’s orig, the output trans is not “as good as” a ba-2, less L, so it needs some NFB to have low end. Some modern recreation; why? There’s no gain control. Make a BA-2. Make the Lassoharp 3 stage BA-2. Etc etc etc ymmv fwiw…..

 

[mrtnasty]

I have 4 bc2b preamps which I plan to recap and wire up. They are 40db gain. I plan to follow Emrr's NFB mod, but I was thinking still I might not have enough gain for ribbon mics. Ive used the 12ay7 to 12ax7 swap in guitar amps before and was just curious if anyone had thoughts on this for the bc2b preamp. Thanks for your replies.

 

[emrr]

12ax7 would certainly have decreased gain and higher distortion driving the output transformer. Don’t use a load resistance on the output, you’ll have 7dB more gain. Rewire the output for 600 rather than 150. Also more gain.