I agree completely that the QSK board is easily damaged in tube arc-over. But it's an exaggeration to say the parts aren't available through distributors. Mouser has 26000+ DIP CD4011B's in stock, and there are plenty of superior NPN and PNP transistors. The bias transistor ESPECIALLY needs an uprated replacement, not the cruddy original-spec one, and adding zener protection around it is especially wise.
The number on my ICs is not carried by Mouser, nor were any of the transistors. The transistors found on my boards were not those shown in the updated schematics. None of them were available at Mouser or the other USA parts houses. You seem to have some info many of the rest of us do not have, but could certainly use. Perhaps you can recommend a replacement for the 2N3055 bias transistor and others, such as the transistor that controls that bias transistor. I believe that is a MPSW42 on my board and all the replacements I've found are also obsolete. Are there other better 100 V 1 watt transistors available? Thanks in advance for your help in identifying the devices.
The MJ15001 was the Ten-Tec recommended upgrade to the 2N3055. The upgrade has a 140V rating (as opposed to the original 60V for 2N3055) but will still tend to fail shorted in the case of a tube arc. I recommend also "wrapping" a 60V transzorb around this transistor (e.g. across the 150K 2W resistor used to develop bias voltage, and is shorted out by this transistor.)
Mouser 60V Transzorb part number: 625-5KP40A-E3/54
Mouser MJ15001 part number: 863-MJ15003G
The MPSW42 is mostly obsolete today. KSP42 is equivalent (300V 0.5A). Mouser part number 512-KSP42BU
None of these parts are all that exotic. The cost of these parts is completely trivial compared to the HUGE PITA it is to get to the parts in the amplifier. It is such a pain to work on these. That's why I recommend the transzorb.