IS THERE ANYONE HERE WHO CAN EXPLAIN THE FOLLOWING. 5AR4/GZ34 RECTIFIER TUBE, AND 5AS4 DIFFERENCE. BOTH HAVE THE SAME CONNECTIONS. THE 5AR4 HAS A SEPARATE CATHODE, ALTHOUGH IT IS CONNECTED TO THE FILAMENT PIN #8. THE 5AS4 DOES NOT HAVE THE CATHODE AS SUCH. ARE THESE TUBES INTERCHANGEABLE. IF NOT, WHY NOT. DOES IT REALLY MAKE THAT MUCH DIFFERENCE. MURRAY (VE7MGY)