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Re: 807 vs 6L6

Posted by cjs on January 31, 2005 at 20:17:28:
VERY unlikely that anyone would have a single amp that could use both tubes; 6L6 is a standard octal, 807 uses a 5 pin base and an anode cap,-- serious experimenters only. That said, I also don't really think there is an "807 sound" or even a "6L6" sound. Yes, the 6L6 family is said to have nice bass, "pronounced, forward midrange" etc. etc etc, yet a lot of what is heard is the AMP, interacting with the tubes, not the tubes themselves. Many will disagree; Then, of course, there are folks with opinions on tubes they have never heard..... :0) Here is what is absolute about 6L6 and 807: they are beam tetrodes. The 807, in VERY loose terminology, is a sort of "super" 6L6 (or "baby" 6550!) Early versions of 6L6 like 6L6G, 5932, etc are wonderful tubes-- the black glass Sylvania and TungSol 6L6G are among the finest beam tetrodes ever made. Unfortunately, they are critically hobbled by max DC ratings of 360 VDC plates (some do 400 VDC) and just 270 volts screens; these tubes must be run either in true tetrode or with a tertiary-wound transformer to get any real power out of them. Ditto for the 807, except that the plates will take nearly 800 volts.... the screens still are locked down at 350 VDC max. This seriously limits their usefulness because running them in tetrode, like in the Altec 256C, requires complex power supply regulation schemes for the screen supply. In class B, with 675 VDC plates and 300 VDC screens, a pair of 807s makes a LOT of power quite gracefully. There are several dozen variations of each, each with a slightly different "flavor", produced not by that tubes' "sound" but by the interaction of the tube and its' application. If you do not need a lot of power, or are prepared to use the Sowter reproduction of the Acrosound TO350 w/the tertiary winding for the screens, both tubes are a hell of a bargain because most folks skip over them due to the above limitations. Probably the single best tube value going anywhere is a 1940s 1625; it's an 807 with a 12 volt heater-- I routinely see NOS Milspec Sylvania and "Hytron" 1625s for about $5 each! This, for a tube that will absolutely thrash any $400 quad of XF2 Mullard EL34s ever made! The tertiary transformer is the way to go; it uses a truly independent winding for the screens, not just a screen tap on the plate winding like in Ultralinear. This allows much lower voltages to be used on the screens than the plates, while still maintaining tight reign on the screens unlike in tetrode. Tim Di Pavricini, in his TOO COOL E.A.R./Yoshino designs uses the magic of tertiary to use his "pet" tube, the EL509, much like the way an 807 could be used; with less than 200 volts on the screens and big DC on the plates. Those EAR amps are the hottest thing to come around since WZ Johnson rolled out the Audio Research D52 back in 1974. Anyway, for all practical purposes 6L6 compared to 807 is apples and oranges. Both great. Both beam tetrode. Otherwise quite different.