VTA ST-120 and 12BH7's

Hey all. I'm sure this has been addressed before but am having trouble finding a thread on it. Would substituting 12BH7's in place of the 12AU7's in the VTA ST-120 make a difference in the sound quality for a positive? Better detail etc.. I almost always listen in the triode mode. Also if I were to tube roll would swapping out the center tube make the most difference or should I swap all three tubes? I'm currently using vintage Sylvania (circa 1950's) 12AU7 organ tubes in all three slots. Also is there a gain factor I would need to consider and any favorite brand of tubes among the forum that seem to produce the nicest sound? (subjective I know). I listen to mostly classical and jazz with this amp through Klipsch RF-82's. Input is analog (turntable) as well as flac from the computer. It's fed by the SP-14 preamp. Cheers...Leigh

I experimented some with 12BH7's and found them all too dark for my tastes. Same thing with the 5814's. Have some fairly good quality tubes with decent reviews too. I suppose a lot would depend on your room and musical preferences. I much prefer the 12AU7's.



The pic is intended as a warning ... rolling can become addictive ...

Current drivers are a matched set of 12AU7a RCA clear tops with a 1940's RCA foil getter 12AU7 in the middle. I trade that every now and then with a 1960's Marconi 12AU7. Gain will vary from mfg to mfg and doesn't seem all that consistent for a particular type - in any case, the difference for me isn't all that great, requiring only minimal volume tweaks. It's a good thing to have a matched set in the channel positions, with a well matched triode section in the center. That will give you the best imaging.

PS ... I really liked the Sylvania 12BH7's ... and then I went and did some additional hardscaping in the room, adding diffusers on the ceiling to kill some harsh buzzes in the primary reflections.



Before that, the 12AU7's tended to run too bright with piano and female vocals. For me, the magic moment came when I could play Norah Jones without wanting to claw my ears out. Really brought out the details and tamed the upper registers nicely. From then on, the 12BH7's have been on the back burner ...

(And yes ... those ARE floor mats. Local big box had them on sale for $12 each. Memory foam, so they weigh next to nothing and absorb a LOT of sound. Held up with some of those COMMAND removable tapes.)

I'm an newbie with a kit built ST-120 with the capacitor upgrades and 265 hours on the amp using I tunes & ALAC/FLAC files with a MAC mini, dragonfly USB DAC and 1975 Klipsch Hersey speakers with re capped crossovers. 
I'm currently using a pair of matched Sylvania 12BH7 in the right & left positions with a Panasonic 12BH7 in the center right now this sounds good to my ears in my system.
I started and broke in my amp (up to 200 hours) with the kit supplied 5814s and felt they were too bright so i rolled in some 12au7a RCA clear tops with the Panasonic 12BH7 in the center nice improvement still too bright for me so I swapped in the Sylvania's and much better sound too my ears with my system.
My speakers use horns for the mids & highs and are known to be a little shy on bass, for now I'm very pleased with the sound being produced I also have the following tubes to do some rolling/testing in the future
Siemens ECC 81, Amperex orange label 12AU7a, Amperex Bugle boy 12AT7, RCA 12AU7a clear top, Tung-Sol 12BH7a, Philco 12BH7, GE 12AT7wa, Arcturus 12AU7 to name a few addiction? I believe there is an intervention in my future
Your ears are your best guide for you with the system you have.

With Tung Sol KT-120s I am finding I can go back and enjoy the brighter sounding preamp tubes that I first rejected as being a little hot on the high end.  Like the Radiotechnique 12AU7WA and CBS Hytron 5814s.  

Plus with the cap changes I did last summer I am finding that it took a good six months for the amp to settle down and "break in".   So give your amp plenty of time to bloom.

arledgsc wrote:With Tung Sol KT-120s I am finding I can go back and enjoy the brighter sounding preamp tubes that I first rejected as being a little hot on the high end.

No tube is an island ...

Comments do seem to support my findings as to bright and dark here ... relatively speaking. Room's too bright for your tastes, go with the 12BH7 or 5814 varieties. Need a high end boost, go with the 12AU7 varieties. Sounds simple enough, but I'm sure there's all sorts of exceptions.

Any volunteers to tack some carpets to their ceiling and see if their preferences change like mine did?   

Great advantage to tubes. A simple swap can make a world of difference in what you hear ... not so easy with solid state.

Still can't forget room treatments though. Bright or dark is one thing, but you still need to address any major eq issues and/or reflections for the best possible results. I think I'm getting really close here ... and it's only taken 30 years!   

PS ... you think rolling is fun, wait till you get into RTA ... takes the guesswork right out of proper eq. Software driven, add a mixer and calibrated mike plus an ADC to feed the system, and you're in business.



Used to take trained professionals to come into a home and voice a room properly. Not to mention a lot of bucks. Now you can do pretty much the same thing yourself for a couple hundred invested. Once you've crunched all the numbers, it's fairly easy to transfer your tweaks to hardware.

Thanks everyone. I have a good acoustically balanced room I think (carpet, couches, and acoustic ceiling tiles) and don't experience any "over brightness" in my system at all. I will probably stick with the 12AU7's for now and try the 12BH7's when I'm in the mood to tube roll just for kicks to hear how they sound. Certainly can't hurt!

Cheers!

Leigh