mk2 external bias ????

[tacobender]

So I built an mk2 with an external bias, using new stock oc75 for q1 and new stock ac128 for q2, and a vintage oc76 for q3 with bias 10k Lin to replace 8.2 collector and worked wonderfully. Then I got a stock of Nos ac128's so I took out the new production germs and left oc76. The bias before the swap out worked perfectly with a nice sweet spot in the middle an zippery gated fuzz when all the way up. Now after the swap the bias pot only works about half way before break up and then nothing, no sound. So what's the deal, I measured the transistors they were about the same hfe and leakage so idk... any ideas. Thanks.

[tacobender]

Calling all cars... anyone have this problem?