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Old 3rd September 2009, 04:20 AM   #1
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Default Obliterate, delete Vibrato or Reverb circuit in blackface-like amps

Anyone knows how would you delete the Vibrato or Reverb circuit from a Fernderish Blackface-like circuit keeping the tone the same?
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Old 3rd September 2009, 03:36 PM   #2
jjman is offline jjman  United States
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Assuming it's NOT a Princeton Reverb circuit, to keep the tone exactly the same you would:

-Don't plug in a pedal to the trem jack. This will keep it off.

-Keep the reverb knob turned down.

Pulling the Trem tube would disable it further but would increase some voltages on some tube a hair. Pulling the reverb send tube would disable the reverb completely but would also increase the voltages on some of the tubes, albeit also only a hair. Pulling the reverb cables out would also disable the reverb but not change any voltages. Disconnecting the Trem intensity pot will remove the default "attenuation" it provides and would thus change the tone.

If itís a Princeton Reverb all is the same except you cannot pull out the trem tube since it also performs a function for the main signal.
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Old 4th September 2009, 07:18 AM   #3
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I was talking more about what would happen if you leave those parts of the circuit off the design. How could you do that without changing much the tone, if it is possible and such. I mean in the schematics available the Reverb and Tremolo sections are clearly defined. Can you just ignore the from your design and have a simpler one?

Now that you mention the Princeton, yes part of the tube is used for reverb. Can you use just half of that 12AX7, leaving the reverb circuit out? This kind of things are what I'm talking about. Can you ignore all connections going to those parts of the circuit in Deluxes and Twins aswell?
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Old 4th September 2009, 10:19 PM   #4
jjman is offline jjman  United States
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Yes you can use just half of a 12ax7. You should also look at the BF Bassman since it has neither Trem nor Reverb. Just ignore the “Bass instrument” section of the drawing. Also look at the other non-Reverb BF schematics.

If you focus on one section at a time you’ll see how similar they are between the models. If you merely “erased” the reverb and trem sections on a BF, it will work. Just watch out for shared components that will no longer be “shared” and thus will need adjusting. Like shared cathode resistors. And fine tuning the dropping power resistor string, as a final step, is appropriate since you are reducing the overall draw on the power supply.

If you understand schematics and respect ohms law it’s pretty easy to eliminate the stuff you don’t want. I built an amp that has a Tweed Deluxe output, a Trainwreck Express preamp and PI, and a 6g9a Tremolux Tremolo combined. “Cut, paste and adjust” as apposed to “erase and adjust.”
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Old 16th September 2009, 01:13 AM   #5
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Yeah, that's what I was wanting to hear! Good to know, really thanks for you reply, I'm more confident now. I knew it could be done, but not exactly what to look for, now it's a bit more clear for me to work it out.
Again thanks, from Argentina.
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Old 16th September 2009, 03:47 PM   #6
jjman is offline jjman  United States
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Here's a thread on TGP on the same topic. My assumption was that you are also the person on this thread. Or it's just a coincidence.

http://www.thegearpage.net/board/sho...d.php?t=601134
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Old 23rd September 2009, 03:23 AM   #7
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Wow no, I'm not. Now that's a coincidence... I've been doing similar modifications...
Had I found that thread before I probably wouldn't have posted here...
again thanks, things are going great with the project, I'm checking voltages here and there now, only need to buy the expensive parts, you know tubes and transformer... not as easy to get as in the states.
By the way that thread is really useful... learned a lot
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