Try this thread :
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1338672552&read&keyw&zzm8080
I had the PV 14A a few yrs back and it came equipped with Mullard 6C4 M8080 tubes. Many think this tube is the best. You might get them from CJ or from Watford valves in England.