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Dynaco ST-70 kits

javajam12

javajam12

Active Member
Hello - I am interested in the Dynaco ST-70 kits and was wondering if anyone has experience with the different kits available such as the Dynapart kits and the Tube4hifi kits. I know there are quite a few threads about the ST-70 and all the mods one can do. I have not seen much about the major differences in the kits available though, I apologize if I am treading familiar territory. Am I to understand correctly that the Dynapart kits are more original in form and the Tube4hifi ones perhaps a little more refined in parts? I would like to get into tubes soon and wondering if it would be worthwhile to look into these kits? I currently use McIntosh and some Marantz separates and would eventually like to gravitate toward a tube McIntosh amp such as the MC275. However, I can't quite afford that yet so am thinking about trying out the Dynaco ST-70. I do hear nice things about these amps. It appears that one can spend as much as one has on these. I see original ST-70's on ebay for as little as $200 that would presumably need plenty of care and modding as well as pre-built modded kits for upwards of $800. I'm not quite sure I want to build one of these as it has been my experience that kits can end up costing the novice as much or more in the end. I can do basic soldering and the like but am not sure I am up to building the amp. Anyone
have some experienced opinions to share? Thanks for the help and guidance
as I would be lost without the AK! Java
 
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Your story sounds a lot like mine a year ago. I too gravitate towards the MC-275 but could not bring myself to spend the money. I bought one of the tubes4hifi ST-70 clone amps assembled by Bob Latino and I have been extremely happy with it for the past year. I thought about getting the kit but I think he only charges around 100 bucks to assemble it and that was worth it to me as he has assembled a lot of them and does a nice job. I use it with a Conrad Johnson PV-5 and I think it sounds very good. I would order it without tubes and choose your own tubes instead. My understanding of the Dynakit parts one is that their driver boards are modern versions of the original dynaco board whereas the tubes4hifi is a different circuit design that uses three 12at7s instead of the two 7199s. I have been very happy with the amp for around a year now. It sounds great and has worked perfectly.
 
Thanks for the advice. I guess I have a lot of reading to do about tubes! Wow,
what a wealth of information just in this forum.
 
I've had multiple ST70's over the years and still have one awaiting some future hotrodding. I've also got an original MC275. Tough to find any comparison of them except that they have tubes in them. The MC275 sounds anything but tubey to me whereas the ST70 certainly does. I like them both.
 
hey-Hey!!!,
Given your eventual desire to have a more expensive amp, I would suggest a crusty, ugly original St.70. Learn while you resurrect it, and you'll be better able to deal with a more 'spensive McIntosh. Given availability of new production output TX's( and option's on those ), you could even get a chassis with just a power TX on it and go from there.

I am looking forward to my next Mc's; I got a lead on some over vacation...:) They'll fund some interesting DIY for sure!
cheers,
Douglas
 
Stock ST 70, before im using svetlana el34, presently im using 6L6GC & im enjoying using it:banana:

28122007697.jpg
 
I haven't seen the OPTs, but the power TXs from Triode are a marked improvement over the original. Check out the difference in the stack.:yes:
 
Here's a pic of the setup that's currently in my living room:

http://tubehacker.com/events/cornwalls/

I belong to the SMAC (Southeast Michigan Audio Club), and as a consequence I've heard a lot of different amps, both OEM and DIY. The amp that kept sounding "the best" to me over a wide range of setups was the "Keggerized" ST-70. I was fortunate enough to have the Keg Man himself walk me through the buildup of one of these amps, and I rehabbed a rust-bucket of an ST-70 to be what I have now. The only parts that are still original are the chassis, cage, sockets, and cloth lead OPTs. Jay is right, the Triode PT is a great upgrade: It will allow a larger range of output tubes to be run, and it runs a LOT cooler than the original. The driver board in the Keggerized version is a tweaked VTA PCB. There is a UL/Triode switch for each channel between the output tubes. The can cap is a modern replacement. It has a little hum with the Cornwalls, but I haven't heard any with other (less sensitive) speakers. The damn thing driver a speaker like a SS amp! It's got guts from hell! In the end, the build is similar to the "Bob Latino" ST-70 that was mentioned earlier. If I was not DIY inclined, I might opt for the Latino version, but truthfully this is a pretty easy DIY project. It would be totally suited to a handy beginner.

Pretty wood face on that ST-70 you got norelco!
 
Man, that's a nice setup Squidward. I've heard about Kegger's skill with stereo 70s. Mine is an older mod, but I can't remember who's design or which magazine it came from. It's running KT90s, but they are a definate stretch with the stock PT. I'm either going to replace it with a Triode one, or stack another cloth lead one on top and paralell them. The 4 small tubes are 12AT7s. If anyone knows anything about this particular mod I would love to have some info. I know what you mean when you say these can drive like SS. This one has driven every speaker I've tried with no trouble. The outputs are truly special.:yes: Here's a pic of it sitting next to it's little brother, a ST35.:thmbsp:
 
Nice '35, Jay! DIYTube PCB, I presume? I have one as well (tho not as pretty), and it's a very nice amp itself! I was recently over to another AKer's house, and he had one running in triode mode. It was a VERY sweet 8WPC!!!

I have seen that ST-70 mod you have before, Jay. I can't remember what it is, but I'll pass it on if I remember/find it. Did you buy yours on Agon? I seem to remember an ad for one there like that a long time ago.

I would be worried about running all those extra tubes off the stock PT. I'm a chickenshit when it comes to tube stuff tho, always worried something will catch fire! Cooler running PTs are for me the way to go. The triode PT is an excellent piece of iron, if you went that route it would look very nice & clean, and run great. One of the other things that's awesome about the Triode PT is that the teflon leads are so long, you can wire up the rest of a '70 with them when you're building from scratch! Then all your wire matches, and is very very nice!
 
Yep DIY board and original Dynaco iron. I'm trying to figure out how to add a switch to the 35 to go from Pentode to Triode mode, just haven't had time lately. The 70 was my first real tube amp and came from Epay a few years ago. You're right about the PT, it seems to do OK on EL34s, but the lams actually rattle with the 90s and it gets hotter than a firecracker. I don't use it at present and it's in the "when I get some time" area too. Thanks for checkin on the info, this thing would be a bear to reverse engineer.
 
I am not a fan of any wire run longer than it needs to be, and I'm a cheap bastard, so I usually use a pair DPDT switches for a stereo amp's Triode/UL switch. Using a 4PDT is nice for the "one switch" convenience, but I find that it makes for longer wire runs, and they're harder to source (rat shack doesn't carry them, and a pair of nice DPDTs can be cheaper). I would think that you'd probably do the '35 a lot like the '70, with a 100 ohm resistor from G2 to G1. On my '70, putting the switches between the outputs has let me get away with almost no extra wire at all: The UL taps go to one of the switches input, the other has the 100ohm resistor going to G1. The output has a very short run to G2 on the output socket. The same setup, or something similar, would probably work on the '35.
 
Dynaco ST70

Hi guys,
Has anyone had experience with Tom Tutay's rebuilds and mods ?

Thanks.
 
I've always wanted to get an ST 70, but will they run a set of Dahlquest DQ 10s? They are pretty power hungry!
 
I've owned a Panor ST70 II from the early 90's for some time, bought it as a demo model, rock solid dependable. I've since upgraded all coupling caps. Sounds very good but I've never heard an original. It uses 6GH8A driver/inverter tubes which need to be descent tubes or it will sound a bit harsh when played loud. Luckily they are cheap tubes for tube rolling.
 
Marantz7t15 said:
I've always wanted to get an ST 70, but will they run a set of Dahlquest DQ 10s? They are pretty power hungry!
Click to expand...

I'd be inclined to find something a little bigger for DQ10s... from personal experience, with similar size amps.

I'd say, at LEAST 50-60w/ch, tube, to drive them. Solid state, at least 100w/ch, preferably 150+ watts per channel. My benchmark is the Crown DC300A-II... that's the BEST I've ever heard DQ10s sound, PERIOD...

Regards,
Gordon.
 
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