The new ST70s

Fisherdude said:

Yep, that's it. Insulated all the way to the end, and the little clip sticks out when you want.

Why just the ground probe, tho? I like it on both. Clip the neg to a ground ref point, then the other to the test point. I just never feel comfortable holding a plain point while I turn my head and look the other way.

Click to expand...

They can be used for either. They come in red and black. That's just a pic I found on epay to illustrate your good point.

Just didn't want to see anybody fishing around live circuits with alligator clips. OUCH!!!!

Rick

this is a great post! I ordered the VTA board about a week ago and have been waiting paitently. Very nice fellow to talk with.
Kegger, if you could point me in the right direction with assembly shoot me an email.

How is the construction coming along on the new Dynakit?
(When you get to the VTA part get a hold of me)

I've got Arm013's here at my place.

ST70s, new, used, upgrades, etc

Hi everyone,
my first post here at AK, I've heard my name has been mentioned a few times so thought I'd see what's happening here.
This post started with discussion of building new ST70s, I've built quite a few using all new parts over the past few years (actually built a NEW one using all NOS parts nearly 20 years ago!) and it's great that someone has finally started offering all the needed parts from one place. But for those who want to make a nice amp a GREAT amp (in my opinion) the parts cost of the VTA (tubes4hifi) mod is nearly identical to the original, and in the past I have offered complete kits this way, but I'd rather just offer the PCBs than supplying all the heavy/expensive parts for the complete amp.
I also have a customer who WILL build a new amp for anyone, and the price is only about $150-200 more than the price of the kit from DynaKitParts, so it's a real deal.
Also as Kegger has mentioned, making the switch to 12AU7s or 12BH7s is a real simple plug in deal with just a few minor parts changes, and this is recommended for those with very high effiency speakers), others like having the extra gain the mod gives, along with the totally neutral, transparent, wide bandwidth & soundstaging. I haven't tried his latest suggestion of removing ALL loop feedback (I only use 13db compared to the original 20db) but will try it soon and report back. Many customers have wound up replacing MUCH MORE expensive amps with this amp because the sound is GREAT MUSIC, not just alot better.

The construction is coming along just fine. My soldering technique is better than I expected, though the tube socket lugs & bias assembly lugs were hard to make a clean-looking contact. As this is my first DIY foray, I've had to invest in a lot more extras than I've expected, and that adds up. Though I will say I'm glad I went with a Weller soldering station, purchased a couple extra soldering tips and quality solder. A few days of inhaling lead smoke (even with a fan) caused me to go out and buy some gloves & a $40.00 respirator. I look rather silly, but as much as I don't want to have children, I'm not sure I want to go sterile.
Additionally, I've ordered a nice graphing calculator and a new Fluke multimeter (Fluke 115), as I will most likely be troubleshooting when I power this sucker up (within the week). Word on the street is that a nice multimeter is an essential DIY accessory, though I reluctantly parted with the better part of $200 for it. The graphing calculator is for some math and/or circuit analysis courses that I might take in the Spring, and it comes with a USB cord so I can download some great electronics programs off the internet. I can only imagine what can be accomplished with some experience, reverse engineering, and a sound foundation in the principals of electronic theory.
At the moment, I'm waiting for the tubes to arrive. I ordered two Sovtek 7199s, four Electro Harmonix fat-bottle 6CA7s, a Sovtek 5AR4, and two JJ/Tesla 12AU7s (for the VTA board), all matched. They should be here on the 29th. I feel like a little kid on Christmas Eve.
I ordered the 7199s because I'm building the amp to current stock spec to allow my ears to get accustomed to the sound, then proceed to the two modifications I've purchased. So it may be a couple months before I'm picking Kegger's brain about his suggested VTA tweaks (12BH7s vs 12AU7s, hmmm...). I think everyone can understand how fair it is to wanted an informed opinion about each mod, each step of the way. Maybe I'll even feel experienced enough to take some measurements with the Fluke, just for that quantitative edge.
I should stress how helpful everyone here and especially Kevin at Dynakit has been. He's promptly answered every email I've sent during construction, and without asking, shipped out a 1k resistor to me to replace one I chipped while soldering it to a tube socket. The guy's a real sweetheart, and though everyone's got their 2 cents about how a authentic Dynakit reproduction should be offered, I honestly believe the tech support is top-notch and can grow to offer component alternatives as their finances allow. I really think I went a great route.
Lastly, I don't really accomplish much on days I work (invariably a 7-hour shift, starting at 5:30 AM, constantly moving on my feet, with no lunch break), so my DIY work proceeds on my two days off; not quite as fast as my obsession desires. Additionally, I'm reading a couple texts to educate myself on electronic principals, so I'm trying to balance my time off (aka soldering time, LP buying time...) with learning my smarts.
All this, and I haven't even tweaked (or serviced) the Klipsch Fortes I got a couple months ago...

Question: what should be my first mod, my Triode cap board or the VTA board?

Best,
Benjamin

Hey Roy thanks for chimming in.

Brinkman thanks for the progress report, have yu taken any pic's?
I would do the cap board first as the upgrade, for it will benefit both
before and after the VTA upgrade is done. Cool to see yu getter done!

Keep us updated!

I can post photos using Tinypic, but I don't know under what menu I can shrink the photos down to suggested forum viewing dimensions. Any suggestions (I'm using iPhoto)?

Best,
Benjamin

I just use Paint to resize photo's and upload through AK with the advanced
post a reply button then just point to the place on my pc and send em up.

or just use www.imageshack.us and do the thumbnail for forums, works every time

Figured photo-resizing out. The HELP menu bar really, um, helped me out. Will post photos after lunch & job interview.

Best,
Benjamin

Alright here are some near-completion ST70 photos:


This is a close-up detailing the non-stock ceramic tube sockets in profile. In the background is my Weller soldering iron and my "helping hand" with magnifier.


This is a detail of the power supply board. I'm satisfied with my soldering so far.


This is a nudie pick of my ST70s bottom.


This is a close-up of my rats' nest of wires, some of which were left untrimmed anticipating the eventual istallation of Triode cap board.


This is the stock bias assembly.

Hope ya'll approve!

Best,
Benjamin

Photo's are just a weeeee bit small but we get the Picture none the less!
Looks great, thanks!

Keep us posted!

Sorry about the little pics; I was recommended said formatting without having seen the format in practice... but hey, who cares, I got my tubes today!
If only the company party wasn't tonight.
Tomorrow: multimeter arrives.
Within the week: variac arrives.
FYI, I'm not waiting on the variac to power up the ST70. Can't wait to have it in the arsenal though.
Soon enough I'll be posting "action" photos of the ST70... my Klipsch Fortes have been practically begging for it...

Best,
Benjamin

I know it's hard to wait but I don't work without my variac on a piece,
even a piece I've had up a million times. Just the feeling is right to me.

Brinkman said:

Soon enough I'll be posting "action" photos of the ST70... my Klipsch Fortes have been practically begging for it...

Best,
Benjamin

Click to expand...

I know the feeling Benjamin the Klipsch Forte's and ST70 were made for each other.

You should have seen the look on my oldest son's face when my ST70/Forte combo blew away his "1000W" surround sound system.

Hey guys!
I threw the switch on the ST70 last night. When I finished the ST70 I was blurry-eyed and had a splitting headache, but I couldn't retire for the evening knowing how few connections were left to solder.
This morning saw me tinkering with the bias and whatnot, finally hooking up the speakers, spinning my first LP...
Well, after almost ten minutes, I noticed some visible over-exertion on the two left output tubes...
So I've powered everything down and am awaiting tech support, but those ten minutes... man! The solid-state shrillness coming out of my Fortes is nil. The mid-range is robust (finally), and I was assessing the bass when my I noticed the problem in tube-land. It seemed to have more bass extension than I expected (re: common criticisms of ST70), but bass detail & definition may need help.
For obvious reasons, I should issue an assessment only after I have cleared any & all technical hurdles, and seeing as this is my first tube amp, these experiences may be more common than I know of during initial bias adjustment/listening trials.

Best,
Benjamin

So what yu got?

I'm currently using an early 1990's ST70 Series 2. It is basically a reproduction on a cleaner chassie with solid state rectification. The circuit is essentially the same as the original. It is a very good sounding amp. I upgraded all the signal caps with MIT's and have it hooked up to my Forte II's. The Mullard EL34 clones are a big step up from EH tubes. I've been using mine off and on for about 12 years and it has been rock solid dependable. Good luck with yours.

Kegger,

I'm going to take notes today as I put the ST70 through the musical wringer. I must say I do have reservations about an assessment from a purely sonic perspective, as that becomes less of an issue when one takes into account the pure joy of a owning a pristine stock ST70, as well as the pride of having built it myself with absolutely no prior experience soldering. It's fairly easy to lose sight of the fact some components offer much more than plug-and-play & specs; an ST70 can have more dimensions to it than any pre-assembled amplifier. It's only honest when one deals with it on those terms.
That said, I will be tweaking it! The pandora's box is open. When does one stop thinking of what to do to their little hotrod?

Destructor,

Unless you or a prior owner has modified it, the series II has a solid-state bias as well as rectification, right? Also, I believe the transformers are of a Japanese stock and the onboard power-supply capacitance is higher. If so, your low-end should have more oompf. At least, that's according to this article: www.tnt-audio.com/ampli/dynaco1e.html. It looks like some of the more popular modifications for the series I ST70 (and dynakit ST70 repros) include elements found in the series II design. Of course, any ST70 with a coupling cap board modification and any one of the many upgraded power supply circuits is a different beast altogether... how different and in what ways is something I wish to explore & post in a methodical manner.

Best,
Benjamin

Agreed it's hard to take the (Proud pappa sindrome) out of the equation when
it comes to sound quality for sure. Was curious how well mechanical it's runnin?

A good performing tube amp with a decent circuit and decent parts should be
very sonically pleasing, then progress as you go to improve where you see fit.