Expanding questions about tubes in a preamp

Not certain if it’s OK to swap 12au7 for 12ax7 in the event your unit has been modified.

Maybe someone here knows.

My only familiarity with 86’s is from re-tubing a couple of vintage Vox guitar amps for a neighbor.

It seemed that he went through 86’s quite often as he had accumulated lots of duds.

I also recall 86’s with shiny/sparkling plates and others with normal dull plates, but don’t recall particular brands (other than the shiny Telefunken I had on hand).

Have you tried contacting the designer of the preamp?

Anyway, what type of noise are you experiencing (gently tapping on the unit will tell you if it’s microphonic)?

If this is it, then gently tapping on either/both tubes will tell you which one (or both).

DeKay

@insearchofprat:
Why change the EF86?
Unless the unit has been left on continuously for 10 years, the tube should have plenty of life.
Putting back 12AU7 will reduce gain about 6db.

Hum could be failing PS in the Wolze.

How is the Wolze interfaced to the HTA-5550?

Have you 'backed-up' from the power amplifier with shorting plugs to see where the noise originates. By that I mean put shorting plugs in the power amp and see what noise appears in the speakers. Then add the next upstream device with shorting plugs.

Just FYI, about 15 years ago when I added HT, every Yamaha model I tried, about 6, hummed. I designed and built recording studio wiring, so it was not user error. Denon, HK, Pioneer, Onkyo were all dead quiet.

Since the HTA-5550 does not need a pre-amp to accept signal from the SA-8001, is the Wolze simply a coloration effect?

Have you tried running theSA-8001 digitally into the HTA-5550?

It has been argued to me that higher end audio component companies are making upfront decisions on the type and quality of the tubes in use.  So, if you have a high end product line, one should expect that the high end line is using the top quality tubes for their product and there shouldn't be a need to upgrade tubes - they were already upgraded in the first place.  Just let it ride.  I understand the desire to dink with sound and search for improvements.  We all do it.  

If a tube is microphonic simply replace it as dampers won't save it and are basically useless (and look silly)...note how many great tube amp designers don't bother with dampers...Shindo, Dennis Had, VTL, VAC, etc...they didn't get the memo? The myth that "all tubes are microphonic" is ridiculous and isolating everything is impossible and unnecessary...just listen to your amp and relax.

Did you learn that in audio school, wolf boy? 😳