Sorry about the tube whine.  I had a similar issue with a Tungsram PC88 that I had in the lead position of my CSP3.  I also use them in my ZMA.  The tube that went bad was in for about one year.  I replaced it with a Russian 6N1P-EV.  (I think the EV is the military version and are more stoutly built.)  Those are great tubes and are readily available from ebay sellers.  I like them in my CSP3 and ZMA but I like the Tungsram a bit better.  The Tungsram are MUCH more expensive than the 6N1P-EVs.  The last time I bought the latter I paid $25 for ten, delivered.  My last Tungsram cost me $17 each!