Perhaps against my better judgement, I bought a used 7236 on FleaBay for my amp. I cleaned the pins, dropped it in, and was treated to really great, tight sound....until about a minute later, when the sound got weaker and weaker and faded to almost nothing in both channels. I shut off the amp and tried again - same thing. It seems like something is shorting out, or the plates are warping when the tube gets hot, which explains why it takes about a minute for this to happen. A bad tube? Or is the 7236 really not the same as a 5998a? The tube has a return policy, which I will likely partake in if there is agreement that this is a sign of a dead tube. What's strange is that this happens in both channels. The heater(s) seems to be working just fine, so could it be the grids? Or perhaps the plates are warping and moving outward when getting hot, which would decrease the amplification factor with distance.....
I also snagged an NOS E80cc for the driver side, and am happy to report that one works great. The 7236 was my real intention, however, in the hopes of lowering the output impedance for my AKG's.
