Conrad-Johnson PV 11 preamp tube dilemma

Did you allow enough run-in time on the Morrow cables? If not, the dull sound you are hearing may be the cables.

Regarding tubes...
By changing from Tele’s to Amperex in the line stage you gained a sweeter, more open midrange.
You could try Amperex 12ax7 in the phonostage.
You could also try one of the Telefunkens in the 12au7 position or an RCA cleartop for some top-end extension. The RCA 12au7 Blackplate presents open, sweet, warm sonics and the 5814A is even better with a sense of realism.
If you are using a Mullard shortplate, it may sound closed in and too warm. If you find you need a warm tube that is more open and extended, Brimar is the tube.
For 5751, RCA or GE triple mica are some of the best.
It’s a good idea to introduce only one tube type at a time so you know which tube is affecting the sonics.

Have you checked the info on Brent Jessee’s site?
http://www.audiotubes.com/12ax7.htm

Also, please tell us what amp and speakers you have.

It would also help to tell us what TT, cable, and cartridge you are using.

So many combinations of tubes shouldn’t sound dull.
I’m really wondering if the Morrows need more break-in.

In addition, I read the PV11 manual and your preamp is phase inverting. From your listening position, does the image sound focused or is the soundstage smeared and coming from different directions?
If phase correct, there should be good detail, and the image should should not be dull. 

One of the MA4 cables is two to three months old.  The other one is new and had ten days factory break-in, but certainly needs a lot more time.  This is the one that caused the problem. I understand it will probably get brighter as it breaks in.  The thing is, the current configuration sounds so good, at least, with CDs, that  I don’t want it to change!
Turntable is an extensively modified Rega RP3.  Cartridge is a typically mellow, but excellent Grado Sonata.  Speakers are modified Dalquist DQ 20’s. Amps are NuForce Ref 9 v3 monoblocks.
I know the amp is phase inverting.  I’ve dealt with it.

Nice cart, I like the Grado sound. OK, so you do need to open-up the phonostage with some dynamics and detail. In addition to my advice above, I’ll add that you don’t need a Mullard in your analogue chain.

Some other 12AX7’s; Siemens (good extension, but Tele’s are better), Sylvania (dynamic, transparent and airy on top), Amperex/Philips (same factory, many different choices). There are Sylvania 12AX7 and also 5751’s. The 12AX7WA Sylvania military is a popular tube. Some Sylvania’s can sound bright, so they should be mated with a less extended tube.

I guess I have to ask the obvious but if changing to the morrow ic caused such a dissapointed sound result that you felt you needed to start tube rolling might it not have been better to just have put the original ic back in the system?

Or were you changing ic because you disliked the sq anyway?

uberwaltz,

What prompted me to use a Morrow cable in the first case was that another piece of equipment I had, benefitted from a Morrow product.  
Then, since that cable (between the preamp and the DAC) worked so well, I installed another identical cable between the preamp and amplifier.  That’s when the dullness occurred.  I happened to have a couple of Amperex 12AU7’s tubes lying around.  I knew them to be brighter than the  Telefunken, so I thought I’d give them a try.
Voila!, the sound opened up.

I would go back to the original cable and return the Morrow cable and tubes.   Use the money for a nice dinner out or buy more music. 

Got you OP.

I hate when an "upgrade" turns into a downgrade!
Its times like that you wish you could just be content to leave well alone. Which is not likely to happen to any of us anytime soon.....lol.

My all tube system sounded great with the morrow interconnects.  But when I switched my tube amp for a SS it resulted in a buzz coming through the speakers, which was immediately eliminated when I switched to another brand interconnect.  Perhaps it is the insulation used? You may be experiencing a milder case of this that manifest itself as a duller sound.

Just from my experience no matter what pieces I have in my system the only cable brand I have tried and that I hear consistent improvement with every tier I move up is Nordost.

I know a lot consider them to be very overpriced, flat, hollow sounding but just for me they have consistently worked.

lowrider, 

Took your suggestions for the 5751 (RCA blackplates-triple) and 12AU7 (RCA cleartop Ecc82.)
i spoke to Brent Jesse about the 12AT7’s.  He suggested Raytheon.  I’m getting them.

Sounds good (I hope). Definitely let us know how it works out... 50 hours for full burn-in.

I will!

Agree with Stereo5, why waste time installing tubes to compensate for a dull perception caused simply by installing new interconnects? No need to overthink, this is not a tube issue, could be a cable breakin issue or maybe a case of it taking time becoming acclimated to the differences.

Put some new JJs in there, that will brighten things up.

Kudos to those who said “wait for the Morrow cable to break in.”
Indeed, the cable changed character and the sound is terrific now. I’m  sticking with the original preamp tubes.
Evidently the tubes in the phono section I bought because they were the cheapest I could find, work wonderfully with my preamp.
I also added high quality power connects to my amps.  That might have had an effect too.

Next time I’ll be more patient.

Thanks for all the suggestions though.