New Fender Bassman 6G6-B Build Questions

[Dave]

As you lower the bias voltage to bring bias current up, the B+ voltage will drop even more. So, yes, I would use a higher voltage tap.

Dave

[72Blazer]

Definitely will do one or the other.  I think I have a 10k pot around here somewhere.

[72Blazer]

Confirm I can wire this Bias pot into this amp using the bias adjustment as the AA864 Layout?  Using a 10K resistor of course.

[sluckey]

This is what I suggested. This allows you to smoothly vary that resistor across the bias cap from 15K to 25K. Just add the red jumper to the pot.

[72Blazer]

OK, I did as Sluckey suggested (jumper).  I am using the red pair of the PT wires.  I got 465v at the plates so I set the bias to 44mA using the 1ohm resistors on pin 8s.  I'm still contemplating installing a multi impedance swicth for the OT as it has 2, 4, and 8 ohm taps.  I'm using the 4 ohm tap for now.  I still have some lead dress work to do but I thought I would share some pics of the build.

[sluckey]

I don't trust the solder job on that chassis ground. Looks like you could take a screwdriver and hammer and with a couple light taps just pop that solder blob off the chassis. Takes a LOT of heat with a powerful iron or gun to make a secure solder connection to a chassis. Using a ring terminal, screw, and kep nut would be a much better ground connection.

[72Blazer]

Noted Sluckey.  I will re-attack that ground.

Vr
J

[72Blazer]

Gents FWIW, I've been playing this amp off and on all night.  Takes my pedals (reverb, delay and a analogman SD-1) very nicely.

The cleans are very nice indeed and when you push it with the volume control on the guitar (G&L 2HB) it growls...
I am sold on this Bassman circuit.  The "Presence" is a cool feature as well.

Time to enjoy this little victory with a stiff Buffalo Trace Bourbon!

Vr
J

[72Blazer]

Thought I would give an update on this amp.

I reattacked that solder joint and it is now a good weld to the chassis now.  I will definitely heed the recommendation for kep nut grounds on future projects.

I added a pot and resistor (exactly as Sluckey recommended below) to control the bias to the tubes.

I initially left out the .002uf cap in the the Bass channel, but my guitarist buddy (using guitar) says it sounds better with the cap in the circuit.  I have a "Cap Substitution" box and we "real time" tried different cap values in the circuit.  IMHO, leaving this .002 cap out did produce more highs-which to me added gain.  There is still a lot of tone control either way using the trebel and bass knobs.  So basically I am indifferent to that mod-which obtw I came across on some thread.
again, this is my opinion only. 

Lastly, the bass channel is louder than the normal channel and gets more gain (using a guitar) than the normal channel. 

This amp would be a great candidate for putting AB swich in front and using the bass channel for leads.

Thanks again to the incredible talent/experience shared on this website.

Vr
J