Rolling Mullard 6DJ8 into GE 5670 Application

Yes, the parameters that work for a designed 6SN7 would not tend to damage an E88CC.  But you could get some improvement by increasing the plate current, which has to be done in such a way as not to exceed the recommended plate dissipation for an E88CC, which might mean just lowering the plate voltage.  Best to leave well enough alone.  Many would argue that the 6SN7, as was, is one of the lowest distortion triodes ever made.

The results are in and the Denafrips Ares II DAC is a clear upgrade for me.

It makes sense as I auditioned the Maverick Audio TubeMagic D2 DAC against the Schiit Modi Multibit and determined that the Modi sounded the same as the tube output on the D2 and I preferred the solid state output.  I then upgraded the D2 with Sparkos Labs op amps which was a clear upgrade with the result being that I then preferred the tube output.  The Denafrips Ares II is a clear upgrade to the modified D2 and is commonly compared to the Schiit BiFrost (or Gungnir), so seems to align with what would be expected.

After putting the 396A tube back in and having mixed emotions about the results, I talked myself into taking a different approach all together and scratching another audiophile itch.

I've purchased a used Denafrips Ares II DAC that I hope will be a clear upgrade for my system.  I did some reading to reinforce my expectation bias, so I've done what I can!

The Maverick Audio TubeMagic D2 DAC is clearly an entry level product (<$250) and marketed as a desktop DAC.  With the Sparkos Labs op amps I believe that it outperforms it price point, but anticipate that the Denafrips will be a step up.

The E88CC is capable of adding airiness, and separation between performers.

They are also adept at allowing the note and vocal to have a perceivable envelope.

They don't overwhelm in the Bass area, the Bass is present, but will be well defined and have an attractive decay.

Any valves I have used during Tube Rolling, that have been hard on the ears in comparison to other used Valves are removed immediately, I can't see how they are to deliver the standard on offer from others being trialed. 

If anyone is interested in the results so far, there certainly seems to be some added clarity, instrument separation, and air around the highs, but the bass also seems to have taken a backseat with some harshness in the upper bass and upper mid ranges.  I don't find it very satisfying when a change yields very mixed results.  I'll let them ride for a while longer and then switch back and see how things sound.  I think I've lost from PRAT with the change in bass presentation.

Best of all, nothing has burned down yet...

@lewm - Thanks for the information.  I don't know if it matters, but the adapter is allowing me to use an E88CC tube in a 6SN7 application which is the opposite scenario.

For what it's worth, it's been running since yesterday morning and so far nothing bad has happened...

It is important to Flag Up a foreseen risk, if one believes it is present.

For anybody who has a knowledge an adapter socket is available and can be used to use a 6SN7 in place of a E88CC, @lewm has made a good information available to be heeded. 

From my end I don't do EE, I step sideways and allow others their opportunity to shine. When the EE extends to my HiFi System the sideways step is enlarged and the work is offered to a select few. 

I have been a social active individual within HiFi for too many years now, and would not change this, I see it as the future for the Hobby.

A Forum is a broad form of communication but is no substitute for face to face and being ears on when experiencing HiFi related products.

I have met with some very influencing individuals who are adept in their Skills for producing sound, some with a career extending over 40 years, specialising in designing / building devices to produce / manage sound.

I am no contender to these individuals; I trust in their work more than I do the mainstream and am fortunate to have developed relationships where contact is always available and visiting them is encouraged even though irregularly maintained.

This all adds up to where I am with a system, the Devices that are the entirety are Bespoke bar One Device. I am using the following: Cart' (Custom Built Design) > Yonearm (Bespoke Modified) > 2 x SUT's (Bespoke Built) > Head Amp (Bespoke Built) > 2 x Phonostages ( One Bespoke Built and One Bespoke Modified) > DAC (Bespoke Design) > Pre-Amp (Bespoke Design and Ongoing Build) > Power Amps (Bespoke Design and Build).

Additional to the above the certain items of Valve Equipment has undergone evaluation of selected components and my selected parts resulting from demonstration impressions made are the ones in use.

Later down the line Tube Rolling was the next avenue of investigation.

The Designer / Builders were given a list of Valves being proposed by a friend with an extensive collection of tubes, that were to be offered for loan to carry out Tube Rolling.

On the approval of the designer for the Valves listed, matched Valves were made available for the Tube Tolling experience.

In relation to the 6SN7, the designer made it known certain Valves that should not be used. 

To have the surrounding support as is on offer, is a very fortunate place to be and I am forever grateful. 

At present the HiFi System is as good as packed away for storage.

When brought out for use once more and is set up in a Room that allows it to deliver to the standard it has been able to, I will get back on track with revisiting equipment discovered over the past year or longer, to satisfy my curiosity for how certain items of equipment will work within my system, as a result of the good impressions made during demonstrations within another system.

I will also be revisiting the 6SN7 idea and seeking out the information from the designer to learn if the method proposed is able to function without any concerns. This is important for me, as when doing a home demo' I do like to experience a newly added device in a variety of configurations.

For instance, when the Nano Core Transformers are used as the first of a selection of Home Demo's, I will be looking to experience these with a selection of owned Valves, Cartridges and Cables.

Such exchanges being undertaken are easy for myself to achieve, as I am well versed and 'hands on' in such matters.

What will be present as always is, is the pre-discussions about the proposed methods with the correct source for the information and working for the benefit of the system. I don't go in blind; I take all advisories given seriously. I look after these special devices, concerning myself for their maintained condition with a vigilance.

  As an aside to the above, but keeping with the subject about being careful and taking advisories seriously.

The following will be more of a familiar day to day occurrence than my practices.

A friend who I trust in relation to the Vinyl LP as a Source more than anybody I know, many ears past informed me the Cue Lever is best used to control the Needle Drop and not just push the Lever Down and Trust in the rest.

I took the advisory on board and have maintained a version of this method to this day. I have even developed the habit where I suspend the Styli, a miniscule distance from the LP. This practice speedily reveals if the LP has Static or if a contamination is on the Styli, as the interference being produced if something is present, is an audible sound from the Speaker. 

The days of Landing the Styli on the outer rim Deadwax and 'willing it' to travel in toward the lead in grooves with a 'skipping heartbeat', are a thing of the forgotten past.

There have been wins for myself, through having been willing to make changes to how a cue occurs for a Needle Drop, I'm sure many are now unknown to me, as I don't believe I had met with all scenario's that could occur.

The Tonearm Lifter used as the Styli enters the inner Deadwax Grooves is one more device that has proved to offer 'peace of mind'. 

Not too long ago, my friend who gave ne the above advisory, was placing an Album to be played and at the time of the cue become distracted momentarily.

They used the older less controlled method and pushed the Lever Down in one operation, trusting in their Cart' alignment. The outcome being a £4000ish Cart' with very few usage hours, was needing to be returned to the Manufacturer with a Skewed Cantilever Damage.

Knowing there is a risk present from a certain method of using a Cue Lever and having consciously done something different to alleviate it occurring for a long time, has now proved to be very satisfying. 

It is not always the Cleaner, Grandchildren, Cat or Dog that are damaging a Cartridge or indenting the Speaker Cones Dust Cover.  

I know I sound pedantic, but the 6SN7 and E88CC are very different tubes electronically, even if you can find an adapter to make a 6SN7 "work" in a socket wired for an E88CC. The E88CC is a high transconductance tube with a mu of 33. The 6SN7 is a medium mu tube (mu about 16) that usually is run with less than 12mA of plate current, usually much less in fact. The E88CC likes more like 15mA of plate current. Also, because of its high transconductance, the conditions that work for the E88CC could conceivably be destructive for the 6SN7 over a short period of time. If you have a schematic, and if you know how to modify the circuit parameters to suit the 6SN7, then that’s fine. Otherwise, I would leave well enough alone. If the tube is serving as a cathode follower in the DAC, the E88CC is actually a better cathode follower than the 6SN7 (because of characteristics mentioned above and other characteristics), which would be another reason to leave it alone. Of course, you can do whatever you want; I am only giving you some facts to think about.

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.

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.

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

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. 

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

 

I’ll be interested in your results. I have an amp that uses 6DJ8. I am currently using WE 396A with an adapter. I have never tried the Mullards.

I will say that I’ve found the red tip Russian 6N5P to be a pretty good option you might roll in sometime.

Jerry

Prior to posting I did reach out directly to Maverick Audio and also Andrew at Sparkos Labs since I put his op amps in it.

When I purchased the DAC it has the GE JAN 5670 tube (upgrade from Maverick), then I rolled in the Western Electric 396A that some recommended as an upgrade along with the Sparkos Labs op amps that were a significant upgrade.  I didn't hear much if any difference with the switch from GE to WE tubes.  I think the tube is a buffer in the DAC, so it's very possible that the Mullard would yield little difference as well.

I do have Focal speakers, so some would consider them to be bright/harsh which may be why the Mullard sound great in my Pathos.  The person that recommended and sold them to me was very clear that his preference is very warm and the Mullard were the warmest he could find.  When I made the switch the improvement sort of defied logic in that it was a warmer sound, but also more detailed and just an improvement in every way over the hodgepodge that I had before.  I've briefly tried some of the "stock" tubes (can't think of the name off hand) and they were awful and came back out almost immediately.

I would ask the manufacturer or the distributor before I would ask here. I recently considered a different brand tube DAC that ran the same tube. I searched on line and saw the adapter and the recommended 5670 replacement tube. In my situation the E88CC was not compatible nor was the 6DJ8. Also in rolling that value tube ( I have a significant stash of nos ), the Mullard was dark and veiled and not to my liking. I realize YMMV , but I had better results with Tekefunken, Siemens CCA, Tungsram, and Tesla. Even the better Russian tubes beat the Mullard. I have dabbled with Rogue gear and they recommend Mullard, but it’s generally used to tame a harsh sound. Although the premium NOS Mullards are well received. But I’d really verify compatibility as I guess it’s not. Also in searching that topic the Westinghouse did seem to be the most poplar substitute. And the price is reasonable. Finding and buying premium medical grade Telefunkens is expensive and ugly these days. I worship my black coated G73-R’s . And I really do like Mullards for a rectifier or power tube. Happy Listening, Mike B. 

The issue for me is not how either tube sounds, but whether or not the two tubes are comparable in terms of their transconductance, mu, and plate resistance, such that you could plug one into a circuit designed for the other and still get the most out of the substituted tube.

Are you sure the 6DJ8 is electrically compatible with a WE396A and/ or a 5670? 

https://www.radiomuseum.org/tubes/tube_5670.html

5670, premium model of 2C51, was introduced in 1946 and its successor was 6922 but it is not entirely the same tube. Some people though claim it sounds better than a 6922.

 

Depends upon what the tube is doing in the DAC.  If it is supplying gain, then yes you'll hear "a difference". What sort of difference is impossible to say without knowing the circuit and even then it would be a guess.  If the tube is just acting as a cathode follower that drives the downstream linestage or amplifier, then the difference afforded by different tubes would be much less profound or maybe not noticeable.  Are you sure the 6DJ8 is electrically compatible with a WE396A and/ or a 5670?  I am totally unfamiliar with the latter two tube types.  There's more to tube replacements than just having a correct adapter.