• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Hammond L-100 conversion

I'm working on converting an old L-100 organ amp into a guitar amp,and it seems like a no-brainer. BTW here is a link to the relevant schematic [sorry I can't find a better quality scan on the inet]


One thing I like about this particular chassis is that it can be used Marshall-style chassis down, and that puts the xformer on the right, there's room for a couple of switches near it on the rear, and the signal flow goes then from left to right across the other side which would be the front. The only slight argh moment is the 5U4 projects over the front of the chassis, hence my question 3 below.

1] you'll notice the terminal marked WH: I figure this is as good a place as any to start the signal chain but am wondering if anyone sees an easy way to use the other half of the 12ax7a and bh7 for an additional gain stage? I'm not too concerned about tone control, though any ideas would be appreciated. Is there a consensus on tone control to rob that could use the ax7a? Is there a no-brainer circuit to utilize that BH7 or AX7 for additional say pre-master gain stage?

2] I initially figured to ditch at least some of the pre-circuitry so I removed the choke that feeds the B+ to the BH7 and was wondering if it would be possible/desireable to use it in place of one of the earlier PS resistors?

3] any bad ramifications if I sub a a5U4GB for the 5U4?

4] if I wanted to throw a standby in, would it go right before the very first 50uf cap? Since this is way over 300v here, can a normal 125/250v switch be used?