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previous: Dan I have a 5F6A Bassman, I never use ... -- 10/16/2004 7:28 PM View Thread

Re: Preamp tube mod

10/17/2004 4:47 AM
Re: Preamp tube mod
Two triodes in parallel will reduce noise slightly and give slightly higher gain. For something a little different try this:  
Connect the spare triode as a cathode follower to the first tube like the tone stack driver except use 390K plate resistor and a 5.6K cathode resistor for the gain stage and a 56K to 100K cathode resistor on the follower. Bypass the first cathode with a 25uF cap. Wire the 390K right on the tube socket to minimize any stray capacitance. Wire the volume pot output straight to the grid of the tone stack driver bypassing the mix resistors. You can experiment with different values on the first tube, I've used a 470K and 6.8K. For extra sweet sound, see if you can find a 1/4W carbon comp resistor for the plate resistor.  
Now that you have an extra pot, wire the bright pot on top of the normal channel volume. Connect the output of the cathode follower through a coupling cap to the top of the bright pot. Disconnect the ground of the bright pot and connect it to the top of the normal pot. Now you can adjust the brightness with the bright pot (it'll work backwards unless you move the cap from wiper to low side) and the volume and brightness won't interact. If you can't get enough briteness, change the cap or add a resistor from the top of the normal volume pot to ground, 470K to 100K or so.

Dan That sounds like a great idea... Do... -- 10/17/2004 12:23 PM
jeremy For extra sweet sound, see if yo... -- 10/18/2004 2:45 AM