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Post subject: help with bias modulation tremolo
Posted: Tue Oct 20, 2009 7:54 pm
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Joined: Mon Oct 05, 2009 10:14 pm
Posts: 33
Hi everyone. i have been studying the Concert 6G12-A schematic. I am considering building an amp and I want to combine the features of my favorite models. I like the pre-amp of the blackface Super with TMB controls, but I prefer the bias mod trem of the brown amps. I need help understanding the circuit of the Concert. The 6G3 uses one triode for trem, but the 6G12-A uses 3. What is the purpose of the additional 7025 between the two channels and the pi?

Looking at the schematic it appears the the normal channel goes straight to the pi, with the vib channel connects with the trem circuit after 3 triodes and then goes to what I think is a passive mixer. This stage looks very similar to the pre-amp stages on the 5E8. So is it mixing the dry and trem signals and then on to the pi along with the normal chan? I heard a vintage 4X10 brown Concert a few years ago and I was blown away by the trem. If i need to follow the Concert schematic to get that sound I will, but i wnated to know about the differances.

Thanks for the help.
Bigampdaddy


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Posted: Wed Oct 21, 2009 8:35 pm
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Joined: Fri Jun 26, 2009 6:53 pm
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Location: Harvard IL
Yeah Bigamp, that three tube circuit is the closest Leo came to true vibrato. Seems like a neat addition to a build, but three tubes and the associated circuit for that subtle effect would make me think twice about it. But you're right, it's very nice. Looks like the oscillator signal is split into two out of phase signals. The audio signal is split to feed the two amplifiers(7025). No, it does not appear to be mixing a wet and dry signal. ART

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