Amperex 6922 gold pin
Siemens 7308/E188CC A frame
Siemens 7308/E188CC A frame
I very recently bought a used 4000. Amazingly good for the money, but when I first turned it on (Stax SRM-T1S/Lambda Sig's only set-up), I was dismayed at how mediocre it sounded. I quickly replaced the Sovtek 6922's with the Phillips 7308's that also came with the machine. Better, but still not so good, IMO. I then started tube rolling using my stash of NOS 6dj8 types that I have collected over the years, since the pre (Melos) in my regular system uses this tube. Here are my findings, and please note that I use the 4000 in an extremely revealing electrostatic headphone only set-up, so soundstaging issues don't really apply the same way; it may be different in your system:
Telefunken 6dj8: Excellent tube. VERY smooth, total lack of electronic glare. Full sounding, maybe a little TOO smooth up top, not quite as dynamic as some.
Siemens (W. Germany) 6922: Great tube. VERY clean and refined sounding. Excellent dynamics. Ultimately, a little too lean for the Stax 'phones. I would imagine that with a different interconnect between the 4000 and the SRM-T1 amp, this would be the one. I use Kimber.
Phillips (Holland) SQ "Miniwatt" 6922: This was the surprise of the three. Not quite as refined as the Siemens, but clean, fuller sounding, and VERY dynamic. And a lot cheaper. That's what stayed in the machine.
All three were FAR superior to the stock Phillips 7308 in every respect,and why anyone would use the Sovteks is beyond me.
As far as the 6ES8's and 7DJ8's are concerned, issues of interchangability aside, don't assume that simply because it is a 6ES8 or 7DJ8 it will sound better. In my experience it's the manufacturer that matters. I have tried (in other equipment) both of those types and I was not impressed; even some "Bugleboy" 6ES8's that I thought sounded awfull in my Melos pre.
Good luck,and I hope this info is of some use.
The 6ES8 is a variable mu tube, not suitable for pre-amp use,
no wonder it sounded awful. The AH! uses the tubes only as
buffers, not as voltage gain devices, giving more leeway in
your choices. As long as pinout is compatible, anything goes
but how it sounds is your call. My 6ES8's are American
Amperex, and they were really cheap in comparison to the
others I auditioned. As always, YMMV. Clyde.
Thanks for the clarification. Maybe I'll try those Bugleboy's in the Ah!, and see. Interestingly, the Melos's manual recommends the 6ES8 "for more gain"; go figure. They did sound awful. Regardless, my point to Douglas was simply that in my experience some tuberollers make the mistake of assuming that because, for instance, a 6922 is supposed to be a premium version of the 6dj8, it will necessarilly sound better than any 6dj8. Not so!
Tried the Amperex "Bugleboy" 6ES8's in the Ah! last night. No, they did not sound as bad as they did in my pre as a 6dj8 substitute, but they sounded strangely dark and, ominously, they ran VERY hot. Nothing blew up, but they were almost too hot to the touch, quite a bit hotter than any of the others, and raised the temperature inside the player to a level that caused me concern; can't be good.
By the way, I tried a pair of Amperex (USA)"PQ" 6922's. Very, very nice. Very similar overall to the Siemens, but a little more body.
Hmm, very interesting. I didn't notice any overt increase in
temperature with my ES8's. I haven't done any tube-rolling
for about a year now and since I have acquired a few more
6DJ8 types since then, perhaps it's time to revisit this
scenario and see if my tastes have changed. It's all very
subjective, with amps, cables and speakers also in the mix.
Thanks for your experiences, very informative Frogman. I sure
find it strange that Melos would recommend the 6ES8 as a
suitable substitute, perhaps it's the tube itself. All my
information says it shouldn't sound good at all, but I'm not
familiar with that piece of equipment.