12bh7 12au7 ok to interchange ?In a vta-st-120 with the low gain board

Hi I see where folks have been using all 12au7 tubes in the low gain st-120 .I thought i was supposed to use a 12 au 7 in the center and 12bh7's flanking it.. so can i use all 12bh7 tubes? can I use a 12bh7 in the center and use 12au7's flanking it ?Thank you for being so nice to the people that love the tube amp sound with the vintage horn speakers.Scott ,finally delighted with my amp.[when i bought it had soft start circuit issues . so i bought it in early 2012 and it has only run well since may 2014 when i got it fixed and now i would like to try some different tubes.thanx again you all are so very helpfuLL Scott Lowe [In not so sunny EUGENE OR

HI bOB IT LOOKS LIKE THE KIT WAS PURCHASED IN ABOUT JULY OF 2011 BUT IT WAS BUILT BY JEFF HOAK , IN BABSON PK,FL BOUGHT IT AND I GOT IT FROM JEFF. HE TOLD ME THE DRIVER BOARD WAS THE LOW GAIN ONE AND TO USE 12AU7 [CENTER] AND 12BH7[ONE EACH SIDE] SORRY TO REPEAT MYSELF BUT AFTER WAITING FOR ALMOST 18 MOS.[I had problems and it turned out to be the slow start so i bought it and it sat for well over a year, and now it runs excellent and i am just being carfull] I FEEL I AM UNDERSTANDABLY CAUTIOUS .i KNOW IT HAS MOST ALL THE MODS : SOFT START AND THE TRIODE OPTION AND IT IS NOW SO STABLE .THAT I WOULD LIKE IT TO STAY THAT WAY.THANK YOU FOR BEING SO KIND TO A NEWBE . SCOTT

Worth mentioning, the 12BH7's do tend to be "darker" than most any 12AU7. That can be a good thing if you like it laid back, especially in triode mode. Also good if your room tends to suck up the highs.

I like it brighter, so they don't do it for me. As is, most 12AU7's are TOO bright, but I fixed that with some hardscaping.

So, basically, each tube type has it's unique sound, and your mission is to match your system so it sounds good to you.

HI, sKiZo what does hardscaping elude to? I thought it meant stones and such in landscaping. I am electrically challenged . I just love the sound of tube amps. So I do have access to a very good tech that does nice work, and I would like to know what that is.. Thank you for your time and expertise.Scott

Scott,

Glad you got your amp issues ironed out, I use a horn loaded Klipsch heresy speakers that are bass shy so I use the 12BH7 in all three driver positions, Raytheon in out board positions and a Panasonic in the center that just sounds dynamite to me.
I'm also using KT-120 in the output positions to help boost the Bass and this current configuration sounds incredible to me, good question about which tube works in your amp as some have different gain as well as a different tone to them the best advise anyone could give you is to keep reading post's on this forum and experimenting with different combinations of tubes that Bob has advised will work in your specific vintage amp and sooner or later you will find a combination that will be magic to your ears and in the process you will learn as much as you want about Dynaco tube amps from some great guys
Have fun
PS I'm in Portland and I have to say the weather has been awesome!

thank you Maintarget .what kt-120's are you running? I also have some hereseys and some chorus and I love em all.As to the weather in the summers are aweome .THAnx again for your time and input.Scott in Eugene.

I believe the only manufacturer of KT-120s is Tung-sol fairly cheap at around $50 a tube with plenty of head room in the VTA ST-120 application they should last for many years.
I bought my Heresy's from my older brother years ago 1976 model ones, seriously looking at building a set of Cornscalas if you don't know what they are Google Crites speakers and check them out, high efficiency horn loaded speakers and an awesome tube amp it don't get much better IMHO.

Shuguang is making KT120s now, or so I hear. Haven't seen them for sale here yet. Supposed to be coming soon to the Psvane branding too?



Price is competitive with the TungSol tubes.

What does hardscaping elude to? I thought it meant stones and such in landscaping.

Thanx for the idea ... maybe some of those styrofoam rocks in the corners ...   

Just another word for acoustic treatments. Involves physical changes to a room with the target of improving audio qualities. Like for instance, maybe gluing carpets to the ceiling ...



Thought I was kidding, didn't you?   

Those are memory foam, so very light, with good acoustic properties. They did a wonderful job of killing some seriously annoying reflections ...

Same pic shows full padded curtains on the front wall to stop a really bad resonance at 160hz that's typical of an over square room. I've also got some other treatments, including a few sections of sculptured foam in strategic spots.



EQs are good for fine tuning, but the room's acoustic properties should be your first defense against bad sound.

Cool sKiZo. I have been working on room acoustics for about a month .And you are so right , It has gotten much better. but the aprox 160 htz hump is temping me to just blow out the wall between two rooms I have :now 12'x12'x8' high.if I did "lose" the wall then the room would be :12'x23'x8'high.When I first got the LaScala my room was I believe 22'x30'x12'high.and i was driving them with a borrowed 200 wpc McIntosh amp and I only played vinyl .[concrete floor]gosh I miss that sound.any room acoustical advice would be greatly aprreciated .[sorry about the spelling]thank you ,Scott

Great minds and all that ... blowing out a wall is exactly what I did here ... getting out the sledge hammer proves you're really serious about acoustics.   

I live in an old cape cottage ... think small. Old pic, but you get the idea. The stereo "room" is really an 8x8 nook with the back wall blown out into an arch. Adding the square footage of the 14x12 room behind it really made a difference.



I did get some strangeness off the top of the arch ... that's where I added the Auralex sculptured foam. Lots of other ways you can handle something like that - mostly it's about breaking up flat surfaces. Walls too - non reflective type hangings, pictures (no glass), that sort of thing. The "cluttered" look can actually work in your favor here. Not seen is a walk in bay I added to the other side of the adjoined room, also open arch.

Anyway ... back to topic ... final tube selection is down the list from demolition, but can certainly make a difference in what you're hearing right now. Bob posted a list of what's available, and each brand can have it's own flavor too. I'm currently real happy with a Telefunken 12AU7 in the middle with a close matched pair of '40s RCA foil getter 12AU7s in the sides.

Just be careful ... tube rolling can be addictive ...

"Just be careful ... tube rolling can be addictive ..."

Yup. I went on a NOS Tung-Sol 6550 buying binge last year and now am three months back on the rent. Anyone want a couple dozen?

Months of rent ?

Here's my collection of "spare" drivers ...



Hi, I'm sKiZo, and I have a problem ...

Haven't bought a new one in months now, so I think I'm over it.

Not hardly, Pilgrim.
If I can unload these 6550s without cratering the market I'll be looking for some nice 12AU7s. The first step to recovery is admitting you have a problem. I don't have no stinking problem.

Hi This is scott and i want to know if it is safe first and second is it worth trying some old EICO ecc83 / 12dw7 tubes that I have.I have a pair of EICO st 40 integrated amps.One is almost mint and the other works perfect but is not as nice to look at but they both use ecc83[12dw7] tubes . so i have 8 and 5 tested very good...soooo I have some nice ecc83's that i would love to try... Is that safe for my beloved amp Thanx so much scott

ECC83 are the same as 12AX7 and generally interchangeable.

12DW7 are NOT the same; though it is a dual triode and the pinout is the same, the two triodes differ in gain.  It's like half a 12AU7 and half a 12AX7 in the same tube.  

The European designation for the 12DW7 is ECC832 (perhaps that was why you mentioned ECC83).  The 7247 is the industrial version of the 12DW7.

GP49 is correct, and you would NOT want to use an ECC832 or 12DW7 in an ST120 or ST70 amp.

Thank you very much ,I am so glad I asked, One last question: is it ok to try the mullard 12ax7's or is that just dumb with the low gain board in my st-120?

you do NOT want to use 12AX7s in place of 12AU7s, they have 5X as much gain !!

and I thank you again. I sure am glad i asked.

By the way, do not throw out those 12DW7s! The EICO amps that used them do have a following and yours could find a happy home in someone's amplifier. You will probably get enough to buy a few CDs or music downloads!