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Discussion in 'Amp Central Station' started by ifallalot, Aug 6, 2019.
I just popped these two out of the center sockets and, voila, half-twin
How does it sound? I'd like to try that with my '70 Twin for indoor gigs and at home.
It just makes it slightly warmer at a slightly lower volume.
I have to get it to stage volumes to really see a difference, but I haven't done that yet. I've also seen that if you replace the 12AT7 closest to the power tubes with a 12AX7 you can get a little bit more gain
If you remove two output tubes in a Twin Reverb, it changes the plate load impedence of the amplifier. You must also change the speaker load from 4 ohms to 8 ohms. So, disconnect one speaker.
Nice amp, ifallalot. Disconnecting one speaker not only corrects the impedance match but also cuts the moving air by 50%. That might do more to lower the volume than removing two tubes.
I did the same thing the other day. I also removed the RCA 7025 from V1 and put it in V6... V1 is now empty so the normal side isn't functional, but that's fine.
Drive pedals sound a lot smoother now. The low end is a little flabby now though. I'll have to tinker with it to see if it is worth keeping it this way.
Next I'll have to change the original Oxford 12T6-10 speakers... but, that is a different thread as it is no longer a free mod.
Removing V1 changes the bias on the second cathode in V2...increases the gain in the Vib channel. I prefer to leave the 12AT7 in the phase inverter position...it is designed to do that job.
Changing from those 12T6 Oxfords will do the opposite compared to removing two tubes and disconnecting one speaker. All 12” Oxfords were changed to have wider voice coil gaps in 1966. This lowered the efficiency and decreased the likelihood of speaker failure. I like the Oxfords in these big Fenders because the decreased efficiency allows one to run the gain on up without creating as much volume. If you are looking for volume, by all means install some other speakers...but you will likely hear a 50-100% increase in volume.