I purchased an Ultra 4A SE with PS 1t power supply directly from Lloyd a few months ago and tried various tube pairs to improve the already super sound. The biggest disappointment was a pair of NOS JAN Sylvania 6SN7WGTA’s that weren’t cheap that I’ll be Ebaying off to a new home. I did hit pay dirt however with a pair of vintage 1954 NOS JAN RCA 12SX7’s I got from a fellow in Holland who had them priced like 12SN7’s. Shazam. All the propaganda about these tubes (at least in this particular circuit) is true. Wider soundstage, better delineation of instruments, richer and deeper bass, vocals that “talk” to you. I drive a solid state NAD power amp from the Ultra 4A and still the quality of Lloyd’s design and the 12SX7’s come through. All my 6SN7’s are now redundant. I should add at this point that my speakers are KEF Q5's and they are of super quality to my ears. Another pair of 12SX7’s I picked up from the Dutchman were vintage 1955 Rogers (made in Canada) JAN 12SX7’s. On some night’s listening I give the Rogers the edge on the RCA’s, but it’s a very tight race. The fellow in question has no more of these tubes left. I bought all ten. Ebay prices tend to the Nuts side of things on these tubes but there is a tube seller in the States who has a swag of GE 12SX7’s ex-Canadian military (although they are not listed as JAN tubes) for US$12 each, listed as used-like new. Cheapest price for 12SX7’s I’ve seen. I’ve no idea how they sound though. If interested send a post for more info.
I have used interchangeably 6X5, 6X5G, 6X5GT, and a Bendix 5839 rectifier tube. The Bendix is a 25-volt unit. I had Lloyd build in a separate filament transformer and switch into the PS1t power supply for me. Mainly I wanted a piece of tube history (Bendix – Red Bank Division) glowing in my pre. The bottom line for me however is that sonic improvement does not lie in different rectifier tubes. Try elsewhere. Oh well, ‘twas worth a try. (The Bendix remains in place just the same.)
If you use the 4A for vinyl listening swapping out the 12SC7’s and subbing Russian 6N2P-EV’s can give a big improvement. My particular 6N2P-EV’s are out of the “Voskhok” tube works in Kaluga, Russia and are probably vintage early 1970’s. They are identified by a neat-o logo of a missile “zooming” horizontally. If you go looking for Russian tubes try for those with the “–EV” extension after the tube number. This means the tube is long-life and “rugged built”. Also, any Russian tube with the “OTK” designation stamped on it means it was individually hand tested to military standards and passed with flying Soviet colours. The improvement with these tubes inserted into the 4A is like night and day. The 6N2P-EV’s are 9 pin miniature tubes similar electronically to the 12AX7’s and easily got off Ebay. I had a hunch about this tube after reading up on them and built an adapter to try them out and the results are a stunning improvement to any LP you play. Because the stock 12SC7 is really a 12SL7 with cathodes common you need to connect the two cathodes of the 6N2P-EV to mimic the 12SC7. Best to have the good Dr. Lloyd set this one up as the possibility of smoke is only a single solder mistake away.
Well that’s it for my opinions. Best of luck and good listening.
Hollow Fate
(Donald Glynn)