New guy here

Hi all. I have been looking at the VTA kits for a little while now and I know I want to build one. I still may be a little way out from actually purchasing one. I'm still "researching" and found this forum. My first question is ST-70 or ST-120. Thats been asked a million times I'm sure. I'm leaning towards the 120. I'm afraid if I get the 70 I'll smack myself on the forehead and say "I could of had a 120". My speakers are a set of Polk Monitor 10a's and a set of Polk Monitor 10b's. They seem to like power. Listening to mostly vinyl. Using an SL-1200. Maybe CD's. No streaming. Looking at preamps also. My first thought is to use the pre out on my Marantz 2245 till I get a dedicated pre. Maybe just a phono pre. I have built 1 other tube amp. A Fender "Champ" F51 clone from scratch, not a kit. And it works! I figure that was a dry run. I have a soldering station and a multimeter. I dont know what else is "got to have" essential tools. So I be lurking and reading for a while. Thought I'd say HI.

Dennis

Welcome Dennis!
I have an VTA ST70. I can tell you that it is perfectly suited for normal listening levels. I don't need the extra power of the ST120. But I understand that it is nice to have it available.

For what it’s worth, buying tubes for an ST 70 is cheaper than an ST 120.

60 watts may sound like a big jump over 35 but with moderately efficient speakers I don’t think the difference is that significant.

I got great sound from both so really I think it comes down to personal choice and how much you want to spend.

Less efficient speakers drove me to build higher power amps so maybe the 120 is the right choice.

The difference in sound level is 3dB You might need it or not.
If you go for a vta70 you will get cheaper powertubes, otherwize they are very similar.
If you regret the buy and the vta 70 you built is in "intended shape" you can sell it and recover
most of the money.

As for tools, a good soldering station, leaded tin ( 60/40 or 37/63 whatever you preffer), a wire cutter
some pliers, screvdriver and a carpet to put on the table is what you need. Plus lots of time.
Do take your time, follow the instructions exactly, if in doubt, ask. Don't rush, don't improvise !

Save the "improvements" to the next amp you will build !

If you've built a Champ from scratch, you'll have no problem with either.

And many believe the EL34 tube in the ST70 to have a "sweeter" midrange than a 6550.

The driver boards are virtually identical between these amps.

Again, with reasonable efficiency speakers, in a reasonable size room and with reasonable volume levels, the ST 70 is a great choice.

I had a similar dilemma years ago when I decided to get a VTA kit. My speakers are Polk SRS SDA 2.3's at 92 dB efficiency. I decided to go with the ST 120. As I recall it was about $200 more than the ST 70, but amortized over the years that cost increase is negligible. I wanted to use KT88 or KT120 tubes; yes, they may be more expensive than EL34 tubes, but the Gold Lion Reissue KT88's are very highly regarded. I like them!

Smack! Do the VTA 120. Lot's of headroom which I really like. The 120 kit from Mr Latino here
is spot on. Everything is included , great instructions and Bob will assist with anything that comes
up.
Welcome to a great site. Dale

Wonder Wart-Hog. Signed by Gilbert Sheldon. Nice.

I got the ST120.

My speakers are 96db Klipsch RB5's. I use it with a Schiit Mani phono pre and a CD player. It has the 21 step attenuator as I don't have a proper preamp yet.
I usually listen around 12 and 1 o'clock from 5 feet away (due listening space issues for now- DONT JuDGE).  It's very clean, fast, and dark sounding to me. I'll soon have 101db Klipsch (Chorus 2's) to enjoy- and yes, from further away too.

Current power tubes: TungSol 6550's
12AU7 Drivers: Bob's mil spec NOS Sylvania 6189's on the outside, Brimar CV4003 in the middle.
I also got a new quad of KT88 EH's for a -too good to pass up- deal on this forum.

As already mentioned, the 120 would give you more reserve power and flexibility.
I don't know enough about this but, you might stay in the Class A part of the amp longer (if this matters???)

Good light and magnification were my best friends during the build.

Thanks for all the replies. My speakers are 89 dB, 6 ohm. I'm currently driving them with a Yamaha A-S501, 85 watts per side. I do like to crank it occasionally. I've put together a set of hand tools. Cutters, stripper, fine needle nose and a collection of small screw drivers. And a few other things I think. I'm a believer of you cant have too many tools. My next thing for the bench will be a magnifier lamp. I have a Weller 60W TC202 station and a spool of 63/37. A Fluke 29. So I think the bench pretty complete. No other test equipment though.

A digital voltmeter is also needed. No fancy however, a cheap 3 1/2 digit will do just fine

peterh wrote:A digital voltmeter is also needed. No fancy however, a cheap 3 1/2 digit will do just fine

But of course. I mentioned the Fluke, that's my DMM..

Going to high efficiency speakers makes a lot more difference in volume than the 3 dB increase of the ST-120. For example, a 35 watt ST-70 driving a pair of 99dB klipsch heresy would be as loud as a 350 watt amp driving your 89dB speakers. If you plan to stay with the current speakers and are used to 85 watts I think the ST-120 may be a better choice. But seriously 3dB is not a huge perceptual difference. It’s typically one click on a stepped attenuator.

I've had many dozens of amps and same with speakers. I've had 350wpc driving JBL100s. I've had 2wpc driving JBL100s (and dozens of other speakers, all medium sensitivity 86-90db).
You can never have too much power, but really not too many people need more than 15-20wpc, that's enough to blow your ears out. 85db with 1 watt is LOUD, not TOO loud, but way loud enough!!
So the choice is yours, it's strictly a budget thing . . . .
BTW, it takes 4X the power to sound twice as loud. So if 35wpc gives you 110db, 140wpc will give you 116db. Either one is way more than enough. If 1w=90db, then 35w= 105.4db

Thanks, that gives me something think about and wrap my mind around. Sounds like with 35 watts and 89dB sensitivity it should achieve over 105db at full volume. Around 102dB at 16 Watt, 1/2 volume approx. It sure would be interesting to have a dB meter and a watt meter. 12 o'clock on the Yamaha is pretty loud. But who knows if that is actually 1/2 volume or 42.5 watts... I know you cant run an amp at 100% volume. I read somewhere that the VTA ST70 actually puts out around 40 watts. But you cant believe everything you read on the internet. The Marantz 2245 will drive the Polk 10s with authority and its rated at 45 watts.

SPL meters are cheap and can be handy . . . $22
https://www.parts-express.com/mini-digital-sound-level-meter--390-722

tubes4hifi wrote:SPL meters are cheap and can be handy . . .   $22

Thanks tubes...  I have one on order.

Mr C wrote:Thanks for all the replies.  My speakers are 89 dB, 6 ohm.  I'm currently driving them with a Yamaha A-S501, 85 watts per side.  I do like to crank it occasionally.  I've put together a set of hand tools.  Cutters, stripper, fine needle nose and a collection of small screw drivers.  And a few other things I think.  I'm a believer of you cant have too many tools.  My next thing for the bench will be a magnifier lamp.  I have a Weller 60W TC202 station and a spool of 63/37.  A Fluke 29.  So I think the bench pretty complete. No other test equipment though.  

Hi Mr C
I'm also a 'newbie' here, recently took ownership of an SP-14 and M125 mono's. I also have 89db speakers, (10 inch woofers). I've got an EL34/KT88 amp. The EL34 is kinda the reason you're getting the mids, I've not even really 'run in' my new system yet, but am already impressed with the sound. What I will say is headroom, I've noticed that the new amps have a better 'grip' on the speakers. You can get the sound closer to your mids with swapping the input tubes, and I will be honest I've become impressed with the Sovtek 6550's fitted to the amps.The M-125's are opening up nicely, clear, good bottom and tops. My 'tech' was here when I set up and even he commented that they sounded promising from switch on.
I'd go for the 120, it gives you 'future proofing' and headroom.

Mr C,
Welcome aboard! If you're not already insane (a penchant for tubes would suggest you are) you soon will be nuts and in very good company here.
Good, basic questions and you got some good answers. I dunno about a rug on the workbench; I painted my top a bright white as it made finding "lost" pieces easier. Light is a huge consideration, the more so as you age. If I could find a cheap operating room light I'd buy one.
I'll skip the basics as you seem to know your way around a homebuilt radio (not to disparage Bob Latino's superb instructions and instant availability should confusion arise) and because they've been well covered.
I'm proud owner of both an ST-70 (den) and ST-120 (living room), and in the past, with lower efficiency speaks than now, a pair of M-125 mono-blocs. My -120 is lashed up to a modified and hugely improved SP-14. Driver tubes are octals, as are all four tubes in the pre-amp.

Here's something to consider, since you're on a budget (aren't we all?) and dipping your toe into the water.

Start with one ST-70. If it's not enough juice for your listening comfort, build another one, flip two switches and run each mono, left and right.
There are no flies on the ST-120, but a pair of ST-70s using El-34s will sound every bit as good as the -120 with the KT-88/6550 outputs, and the tube cost considerably less. If you hunt around, you can find a decent quad of NOS 1950s-era Mullard or Telefunken El-34s (6CA7 is their U.S. nomenclature) for about $60/tube. That times eight for two ST-70s will run you ~ $500. Four KT-88/6550 New Old Stock (NOS) will run you easily north of a kilobuck. So just tubing-up will save you >$500 and probably a lot more. I speak here to the genuine original US-made TungSol 6550 and British-made GEC or Gold Lion KT-88s -- both types of which were manufactured through the mid-1960s.
Different arithmetic will apply if you go to current Russian- or Chinese-made tubes, which are far, far less expensive than the originals and, some claim, are just as good.
My "go-to" guy for new-issue tubes is Jim McShane of McShane Designs, who is well-known to Forum members for his integrity and quality control.
So you've got options. Start with the smallest and cheapest, one ST-70. If that doesn't turn your crank, add another down the road and even Magnepans will roar.

Again, welcome to Tommy's Holiday Camp. As you get sucked down our little rabbit-hole, remember two cardinal Forum rules:
1: The only dumb question is the question not asked;
2. Tube watts are fatter than silicone watts.

Good luck,
dpb

One more thing -- if you're over 40 or thereabouts -- reading glasses and maybe a magnifier.

dave

solderblob wrote:One more thing -- if you're over 40 or thereabouts -- reading glasses and maybe a magnifier.

dave

And more light. Did I mention that? More light. Skin-burning, blinding, operating room, or nuclear blast white light. Unless you like cold solder joints.

Thanks for the suggestions. I like lots of light and I have a 48" shop light right over the bench. and a couple of desk lights. I have a collection of reading glasses. I'm 64, there are reading glasses all over the house. I don't own any tools from Harbor Freight. I had not heard of an isolation transformer, I had to look it up. No Variac, but I do have a DBT and a collection of various wattage bulbs. I usually buy good tools, I like to collect tools. So any excuse to buy a tool. I have an anti static mat over a rubber mat covering the bench. (I stole my wives yoga mat, it almost fit the bench perfect). My big sin is my benches are in the garage on the concrete floor. Maybe if I got a carpet scrap to go under it and my stool. I do always wear shoes out there. I am a member of AK and they been a great help with my vintage SS and speaker gear. One of my other "hobbies" is a 67 MGB I've owned for nearly 30 years. I remember as a kid peeking in the back of the tv set through the vent holes and seeing all the tubes glowing, the heat coming off the back and even the smell. Every once in a while my dad would pull all the tubes out and we'd jump in the Hudson and go to the local grocery store and test the tubes. Every store had a tube tester near the entrance. Most my friends that are musicians have tube gear. All the stereo gear I've owned has been solid state, HK, Yamaha, Marantz. I've had a tube setup on my bucket list for a long time.

If you are working over concrete, shod or not, a bench-based Isolation Transformer is an absolute must. It will not offer 100% complete protection, but it is vastly better than nothing.

Please, also, do not cobble one together from spare transformers, look for an instrument or medical grade device designed for the purpose, and to run all day if necessary.

I would avoid fluorescent devices unless proven 'noise-free', and be equally cautious of the lower-end no-name LED devices.

Welcome! Again!

I'll add my thoughts since I just placed my order yesterday for a ST-120 for my living room.

I have an 8 watt per channel amp in my home office that's a little under powered for me.
Since it's under powered I'm going to wind up having to build another amp to replace it.
So for me the lesson learned was to buy a higher rated amp the first go around and
save the money (and effort) in the long run.

HarryY wrote:I'll add my thoughts since I just placed my order yesterday for a ST-120 for my living room.

I have an 8 watt per channel amp in my home office that's a little under powered for me.
Since it's under powered I'm going to wind up having to build another amp to replace it.
So for me the lesson learned was to buy a higher rated amp the first go around and
save the money (and effort) in the long run.

Hello HarrY.
You're thinking right. Probably not a guy on this Forum who hasn't blown a tweet or a voice coil at one time or another, and in probably 99.99% of cases, the speaker was damaged by an insufficientlyr-powered amp. Solid state amps "clip" -- that is, start shoving DC out the speaker posts which will cook any sized speaker, and right quick. Tube amps clip as well, but you hear a deterioration of sound before blowing the whole works.
For most of us, our speakers are the biggest component of the stereo budget -- or should be. I've never heard of an amp being too big for the speakers.