by TomMcNally » Mon Mar 05, 2007 10:48 am
Hi Greg -
The mods for Hammond transformers are for feedback tweaking, not bias. Are you measuring the bias with the input shorted and a load (speakers or resistors) on the amp ? You can't set it with music playing. If you can't get the bias in range, you may need to adjust the values of the two resistors in the bias supply .... 4.7K and 18K ... you would probably want to try a 10K in the 4.7K spot and maybe go higher, say 22K in the 18K spot. Are you getting about 1 volt on each tube ? The trimpot on the drive board is to balance them, after you get them in the ballpark with the chassis mounted pot. It may take a little back and forth to get it all right.
... tom