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Don't get me wrong I like VERY much what I have. Also 1973shovel is absolutely correct in stating that the VTA can sound VERY modern or almost SS like.
But in it's defense it sounds like what I would imagine (because I'm never getting MY hands on one) what a $15k (insert your own crazy number) solid state amp would sound like. VERY high quality sound.
So again DO NOT get me wrong here I really like this amp. But the advantage of tubes is you can have fun rolling them. So hereeeee weeeee go.
As mentioned by 1973 I also like to have a more traditional/original tube sound at times. Yeah I want my cake and eat it too!
So any recommendations for output tubes that Jim would carry that would bring more of a ST-70 back into the picture.
The only tubes I have right now are the Shaguangs EL34 - a surprisingly good tube and the Gold Lion KT66 - an absolutely amazing tube! Lots of energy on both ends.
The set of 12AU7 that came with my kit are unbelievably crazy good. The ONLY other tube I found to sound decent in that board was the TungSol's. So let's not bother to much with tube rolling there. Already did that with Jim. As was told to me by Bob himself, you can get a LOT of change simply by changing those tubes. And he was very correct. But what it did do was change the amount of detail and background detail - if makes any sense?
charles
Follow Ups:
I've been using 12AU7's but it can take 12BH7's.
can you mix the 12BH7 in the driver position and 12AU7's as the splitters
Yes. I recommend the 12BH7 for the "center" position and then use 12AU7s for the other sockets. It works VERY well!
For my VTA 70, I like the 12BH7s on the outside, a TungSol 12au at center.
Seems a little bit more "laid back" with a deeper, more open stage.
Another experiment for you if you like.
K.
Ok we'll be looking into that soon then.
thanks
charles
Charles, you may find the below post interesting. If you try using those tubes please post the results.http://audiokarma.org/forums/index.php?threads/another-vta-st-70.711531/page-4#post-9700915
Edits: 08/18/16
Hey great read thanks!
Like Bob told me and I've posted that just changing out the center driver tube has a LOT of effect on the amp.
I've tried a half dozen or so in that position but no 12BH7's.
Right now I'm unpacking a new house. And I am SURE that a few tubes didn't make the journey so I feel an order coming up.
I'll keep that in mind.
Thanks
I am thinking about giving the vta70 board a second chance when I get around to putting back together a basket case st70 that I inherited. I'll try the 12bh7's/E80CC combo. I just have to figure out how to paint the transformers without going through too much hassle.
I hope you're tubes made it okay and if not that any that broke aren't the good ones.
I managed to re-paint my 70 trnsfrmrs with engine paint without removing them from the chassis, with a combination of removing end bell bolts and masking the chassis mounts. Took some creative masking and spraying, but I think overall it came out looking pretty good, and a huge step up from the ratty original.
that's great. did you do anything special to remove the rust on top of the laminations or just paint over it?
the Tesla E34L is the tube that I would turn to. If the Teslas are beyond your budget, the JJ E34L should do the trick. I prefer the blue glass version.
Do buy tested/selected tubes from a reputable dealer if going the JJ route. Best of luck with the hunt!
"Do buy tested/selected tubes from a reputable dealer if going the JJ route."
Who would that be?
.......but he does not carry the JJs due to reliability concerns. I have had good service from both Tube Depot and Tube Store and I have heard good reports about Doug's Tubes but have not used him. All carry the JJs.
The Tesla's will be a bit harder to come by, and there is speculation in these, as there is in almost all NOS output tubes, so your guess is as good as mine.
Bob Latino and Roy Mottram,I don't care for the choice of the blue metal oxide resistors used in many places.Notice the resistors I used on this particular board and this actually actually removes most that sterile sound you are experiencing in an otherwise very fine amp.Also,you may want to try a different paper in oil cap like a vitamin Q or Pyramid,as opposed to the K40y feeding the interim stages.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Including tantalum and Riken carbons in a few key positions. I used mostly Dale and a few PRP metal films everywhere else.
I'll get the metal films out of there at some point, along with the Auricaps, which I know how much you love, based on your posts from eight to ten years ago. That's an attempt at sarcasm, if anyone's wondering. Mike had some pretty unflattering things to say about these caps in his posts way back when.
The Auricaps aren't that bad.The only thing I don't like about them is the stranded leads can pose problems like when humidity sets in,the leads going into your cap body can separate and let moisture in.This is turn can cause cap failure overtime.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Not certain if they were Carbon Comp or Carbon Film and I could not locate (just now) the info on Bob Latino's website.
Hum - which resistors did you change? And where can I get VitQ's?
charles
Please observe that Mikey followed Jim McShane's sage advice and mixed the dielectric materials up. Both K40s and Solen film/foil parts are in that build.
Mixing dielectric materials up lets you hear the amp, instead of hearing the capacitors.
Eli D.
All of them.I just buy the boards from Roy and build them my own way..Charlie,if you change the plate and cathode resistors to carbon film along with the grid resistors,this will solve a lot of your problem..You can use Vit Q,Pyramids,or astrons but change resistors first.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Now this is from a schematic I found online because my papers are still in boxes. And this schematic has 12AT7 where as mine uses 12AU7.
Are the resistors you are talking about the following:
Splitter R1 grid
Cathode Inverter R23,27,25
Grid output tubes R33,35
I think that was all I see.
charles
Mike, carbon even over Dale metal films?
when I unpack my stuff and get an actual shop area that will be the first thing I'll do. But it's going to be a while.
So plate, cathode and grid - basically take out all the metal film and use carbon film.
If you go the fix-it route --- try to mod one section, at a time. That way, if you go further from desired end-point... it'll be easy to reverse the mod. I like starting at input, then phase inverter sections.
IMHO, Wholesale mods are a way to instant insanity.
8^)
Right on Steve! I learned that the hard way many years ago.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
I can't agree more.
And yes that was the plan. First the invert, followed by the splitter and then the output grids. Most of the time that ONE upstream part is all you need.
charles
The Sylvania 5932 is one of the warmest output tubes of the 6L6 family. In my experience. Max dissipation is around 22 watts per tube, IIRC.
6L6GA are also a bit warmer in the midrange, but have lower dissipation ratings, 18 watts max.
what plate voltage can those stand? I think a vta st70 puts 430-440ish on em.
I'm pretty sure it can use the 6L6. I'll email Bob and ask???
Yeah, best to contact designer or manufacturer of your unit.
Good luck, in the hunt for perfect tone!
8^)
While anything but inexpensive, AVA's hybrid power amps are excellent. They are costly, but not "insanely" so. I own an early version FET-Valve and its voice is quite similar to that of my "McShaned" H/K Cit. 2.Also, 2 Canadian "name" brands: Bryston and Classe are good sounding and not hideously expensive. Bryston's warranty is very lengthy. They would not offer said warranty, if they knew it would have to be frequently honored. ;> )
JMO, quality SS power amplfication "cries out" for tubed preamplification.
Eli D.
Edits: 08/17/16
Yes, but when most SS amps go to full power with less than 1.0V input (some as low as 0.25V) any tube preamp with gain is a bad match. A solid state amp with 5 or 10 volt input sensitivity is a perfect match for a tube preamp. Tube buffered attenuators with little or no gain are fine, but are really just tone controls.
FWIW, I've never had "hair trigger" volume control problems with my equipment. However, you make a good point. If somebody is going to "mix and match", that individual is well advised to understand resistive "padding" and how to implement it.
Eli D.
Agreed. I think a lot of people lack the understanding of what a system is or how to implement it correctly.
A system where the phono section has enough gain to drive a preamp section that has enough gain to drive the output amplifier that is balance to optimize the gain and matching impedance at each handoff is better.
A cobbled together set of components that has, for example, a source putting out 2 volts, reduced down to 0.1 volts with a pot, amplified back up to 2 volts with the preamp into an amp that has input pots or padding to reduce that back down to 0.1 volts to drive the amp input section that then makes the output signal to the speaker does not make any sense.
I still will pop in a FetValve 300ex and it's really good. It sounds great and never runs out of power. I also have a Fetvalve EX preamp old enough to still have 12ax7s, but I like other things a lot more. It seems a bit too bassy for my taste.
I'm using the Conrad Johnson. Not the warmest tubed preamp I've had but it is the most transparent I've ever had with clarity in spades!!
Bryson - hum
I had my eye on the citation 2 at audio classics. But it will be a year to save up enough to have it McShaned.
I also had my eye on the Mac MC60 as well as some SS pieces. Like the Mac 7100, 502, 2100 (older), Marantz 240, I think that's it?
Charles, what are your sources? maybe they are part of the reason more so than your preamp.
I just wanted to have some fun tube rolling to warm it up a tad.
However Mike's suggestion of putting more carbon film resistors is an interesting one that I may do ONE DAY.
Sorry I don't mean to sound sharp but I am clearly NOT unhappy.
This amp has a very crisp clean sound. Very different from the original 70 but clearly a great sound.
thanks
charles
Let's make this clear - I am NOT unhappy with the amp
that it appears you'll never be completely happy with any amp. It's either "too modern" or not modern enough. You enjoy the chase. :)
Understood. Kegger over at audiokarma knows the board in and out with some interesting ideas. You could message him. I believe the low gain mod, board running 12au7's, was taken from him with a few changes.One easy thing to try that I believe he recommends is disconnecting the NFB wire that goes to the 16ohm tap. Easy to do and worth a try. When I was messing with the same driver board I believe Mike told me to try the same but it's been years.
Edits: 08/18/16
Tung-Sol EL34B
My favorite output tube in the Latino ST 70 is the Gold Lion (re-issue) KT-88. A warmer, richer presentation than the GL (re-issue) KT-66....at least at my house. I've tried several EL 34's, 6CA7's, 6P3's and the KT 88 always comes out on top.
I take it you are looking for a "warmer" midrange tone. Maybe a tad rolled off treble response?
If tube rolling is what you wish to try... maybe look at those 12AU7 tubes. You know anyone that has CBS-Hytron 5418A or 7316 tubes to try? IME, these about the best for the tone you seem to seek. Black plate version preferred. Very good tubes.
Next choice to try maybe the 1950-60s Mullard (Blackburn) or Philips (Dutch) ECC82.
Kinda hard to find good examples of these tubes. Would really be nice to try them out in your amp, before searching the World to find a good set.
Not sure what coupling caps and types of resistors VTA used in your amp. Endpoint voicing could come down to experimenting with specific component types in strategic locations within the circuitry.
Good luck!
EH 6ca7's always sound great in any stereo that I've tried em in. You'll have some fun with em.
It uses metal and carbon films in sensitive positions on the driver board. I'm assuming metal film in path for clarity. coupling caps are K-40 Russians.
I really don't want to start swapping components just tube roll. You are very correct and also reflecting what Bob said about how you can get the most effect by changing the center splitter tube on the driver board.
The driver tubes that came with it were GE 12AU7. One GREAT tube! I tried a few other vintage brandings but my findings in general were a rolled off top end and some degree of clarity degradation. LIke Sylvania, RCA non black plate, RFT, think that's it? The new production TungSols were excellent.
Charles,
You might like the 6CA7 EH output tubes. Have you tried them?
especially if you get the ones that test at a higher GM. There is nothing I could fault with that tube,especially when they stomped on my NOS Mullard XF1s and XF2s.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
No I haven't but I always liked the sound of EL34s. Worth a try. Don't get me wrong the KT66 are wonderful. The beauty of tubes IS rolling!!!
I just moved and I'm SURE there are going to be a few broken tubes to reorder.
Let me unpack and see.
Eli post of possible candidates I had my eye on. My goal is a little vintage sound to match up with my CJ. I already have amps that are razor sharp and new. I miss that vintage sound. My Sherwood fills the integrated slot but I need something to pair up with the CJ.
charles
The Shuguang KT66z may be just what you are looking for. They are 'richer' than the GL KT66.Alternatively, search for Arizona capacitor. These look like modern Vitamin Q's and they hail from Westcap.
Edits: 08/21/16
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