6J7 filmosound conversion issues

[filmdiary]

At the tail end of a conversion job and am having fun trying to figure out a couple of issues.

The original amp model is a 156 - 5Y3, 6V6 push pull, 6SL7, 6J7. The power transformer was missing so I replaced it with one from a 138. B+ was way too high so I found a donor from another 156 but not the exact same chassis model number... had to replace all of the leads as the insulation was completely dried out and brittle but that's another story...

The 6V6's are biasing at around 34 mA / tube or 86%. Plate voltage is 352VDC. 6.3 Volts at all the heater pins and just over 5v at the 5Y3. Should be happy right? Not so much :(...

All seems okay but when I dig into notes on the guitar the signal fizzes out, the plate voltage spikes and takes a minute to come back. The other issue is that on start-up the B+ voltage climbs to 510VDC and takes 7 minutes to drop down to 360. A minute after start-up there is a scratchy sound that lasts until the voltage drops below 400 which takes a good 3 minutes. First time using 6J7 preamp tube so I'm wondering about the power supply and if I need to adjust the dropping resistance between stages. Here is the schematic which is kind of a hybrid of 5A3 and GA20... I've tried swapping rectifiers and power tubes but get the same result. I've got a 6SN7 in there now but dont imagine that a 6SL7 would make a monster amount of difference. Thanks for any insight!!!

If you see any glaring issues please nail me!