Crawls Backward (When Alarmed)

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Modified 5F6A Tone Stack in the Bandmaster clone

Ok, now take a look at this picture.  The black mica cap at the lower left, and the three resistors connected to the top of the yellow .1 cap are going to get removed from the board before you know it.

Poof!  They're gone.

I now have a new yellow wire that runs from the 100K cathode resistor over to the tone controls.  This might make more sense when you see the schematic...

...which is here.  It's the tone stack from the 5F6A Bassman amp.  I just took it and mounted it on the tone controls to keep the lead lengths short in the interest of noise reduction.

The yellow wire going across the board now is the one from the junction of the cathode of the second half of the first preamp tube and the 100K resistor  that goes to ground.  It runs over to the input of the 250 picofarad treble cap at the top of the tone stack.  The rest, as we'll see in a minute, is pretty much wired exactly as the schematic shows it.

To jump ahead a bit:  I first wired it exactly like the stock Bassman.  The mids and treble were much improved.  With the Weber 5E7 tone stack, the mid control didn't do too much, there was overwhelming bass, and the treble wasn't clear even full up.  With the stock Bassman stack, the mid control worked, the treble was much improved, but there was still colossal bass.  I played it with a Telecaster and it sounded like a bass on the low E string!  Part of the issue is the speaker has incredible bass response.

So I used the tone stack calculator from the Duncan amps site and experimented a bit.  The calculator lets you plug in different values and see the changes in frequency response displayed graphically.  Very useful.

Anyway, long story short, I wound up with an .01uF bass cap, and a 100K slope resistor.  Now the bass is much tighter, and the treble and mids are super clear. 

Here's how the tone caps are mounted on the pots.  The cathode line comes into the 250pf cap and the 100K resistor.  The other end of the slope resistor goes to the mid (on the right) and the bass (left) caps, which go to the appropriate place on the tone pots.  It's pretty tidy and cuts a lot of excess grid lead from the circuit.

Here I am doing the wiring on the tone caps.  Gotta love that Optivisor!  Since I got it, I feel strange if I solder without it on.

More coming soon....we're almost done.


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