LM307 replacement/troubleshooting my pre

I am getting no sound from my 2100-65 65W head. All voltages check out in the power amp, but the pre-amp measures little or no voltage at most of it's points. I'm a novice with those LM307 op-amps, so I purchased two new ones and did a substitution test with no avail. Do you think it's possible that more than two of these things could be bad? Maybe I should replace them all. Any help would be great!

You might check at point a on the main circuit board and see if you have +46v at it. This would indicate that your front end is at least got the proper voltage supply for the front end. Also, you should have -46v on point c on the board. A is the 5th point on the board away from the ground and c is the 3rd.

If that doesn't work, and the power tubes are lit, I would look at the 12ax7 PI/driver section and look for bad tube or breaks. The signal leaves the last lm307 and drives through a .1mF coupling cap dirctly into the front of the 12ax7 so it should have signal there. Mike.