Rolling Mullard 6DJ8 into GE 5670 Application

there are many many many 6dj8’s and equivalents... it was a popular tube, used in many applications, consumer, commercial and military, and was made all around the world up to the point where tubes were supplanted with solid state devices in the 80's and 90's

if the tube is in fact in the audio circuit of the op’s dac in a meaningful way as @lewm mentions, there will be many many different sonic presentations available through rolling different 6dj8’s

i still have hundreds (no exaggeration) of old stock 6dj8 variant tubes, made in usa, uk, holland, hungary, japan, india, slovakia, russia and so on... as i used conrad johnson linestages for many years, and they exclusively ran that tube in their better models for 20 years

Based on the additional info it sounds like you’re on the right path. My system tends to be bright and I’ve avoided any silver in my interconnects to correct that problem. The tube “ Sound “ description on the Brent Jesse site is extremely accurate. My pre uses 12AU7’s and the sonic change is very similar to the E88CC change in my power amp. I was fortunate enough to be in your position some years back and nos tubes were not at astronomical prices. My experience with the German tubes is an improvement across the entire spectrum and that appealed to me. It has also been a plus to have a selection to roll with. I recently tried some KT 150’s for the first time and after some break in, wasn’t feeling it. So I rolled in the hottest rectifier tube I had ( a Mullard ). Now I had too much bass , so I changed the E88CC from a Tekefunken to Amperex to bump up the treble. In retrospect I’ve managed to be able to really tune my systems sound by tube rolling, but like stated above I acquired a bunch of tubes. It’s been a pricey but fun experience. Unfortunately I’ve had to attend Tube Addicts Anonymous after my wife saw my credit card charges. 😆 But seriously, Happy Hunting and good luck, Mike. 

 Buell, from your post I gather you may have either substituted for a 12AU7 or rolled 12AU7s. Which is it?

The adapter was delivered last night and I was able to do the tube swap this morning.  It definitely sounds different and my initial response was positive, but I'm becoming less impressed as time goes on.  I'll give it a few weeks and then switch back and see how it feels.

I have early 1960's E88CC Tubes in a DAC as a result of Tune Rolling Exercises and can't get enough of the sound on offer.  

Even now when putting all the HiFi equipment into Storage, it is the DAC > Transport that will be the last Source Equipment to be packaged, I like it to be at hand to be used.

I treat Vintage Valves like a Cartridge, the Values can be high, and there is about a 1000ish hours if all goes well of useful output, even though longer usage can be achieved. My choice of Valves for the DAC has been the same choice for a Friends CDP, and they have an exceptional option from their vast collection of Tubes.

I also have a Hybrid Phon' with Burson Vivid Op Amp's and another Brand of Early 60's Vintage E88CC's. Once more as a result of a Tune Rolling exercise, the DAC's Tubes did not show themselves of in the same manner when used in the Phon's circuit.

Keep options open on Tubes certain circuits can really allow a particular Tube to rise above others in perceived attraction during a period of Tube Rolling.

I can get adaptors and use my 6SN7 collection in place of the E88CC Tubes to see where there are new experiences to be discovered.