• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

What are your opinions of the ST-70 and St-120

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Not trying to start an argument here, but with that logic your "original" dynakit is not a dynakit at all but a indianajo dynakit. ;-)

My point is this, I don't know much about this hobby at all. I am wanting to learn, and to get a good start. I was looking at those kits, it said st-70, st-120, so thats what i conveyed here. I saw other kits that were similarly named, and just assumed they where all varients but similar at heart.

Now to what I am wanting to do,

I have a pretty nice home theater setup using modern store purchased components. Marantz sr7001 as a preamp / NAD T955 Amp etc. etc. etc. None of it is 30k McIntosh, but its good midlevel stuff.

I have an extra set of Klipsch SF-1 floor speakers that are sensitive at 94db @ 1m. And also another set of boston acoustics just sitting around that I would like to do something with.

Which takes me to the point here, in my bedroom I have a crappy little ihome dock or something that I listen to music while tooling around my room. I would like to build a kit stereo tube amp, that looks atractive to put in my bedroom, with probably those klipsch speakers. I want for this to have a nice sound. It does not have to beat out my main listening room, but good enough that I can listen to it while reading at night, etc. And I want it to look very very nice as a focal point in my room.

I really don't want have to use a pre/amp simply because I don't want to sacrafice tons of counter space. Which is what i like about those bob latinos. You can use them with / without a pre. Further, I think they are pretty. But that is literally all that I know about them. Which is why I asked your opinions of them...

So here is what I know about the Bob Latino ST-70. It has much bigger transformers (custom wound if I recall) so it can handle the larger tubes. You also have to learn how to bias your tubes, but it is easy with the instructions and a good digital voltmeter. You can run with the EL34, KT66, KT77, and KT88 (and I think the 6550). Head over to the link below and you can read what Bob Latino has used and what he thinks sounds good in the ST-70.

EL 34 v. KT 88

If I ever get a Bob Latino ST-70, I would go with the following build from all the posts and things I have read. Russian PIO caps, the higher gain 12AT7, the 21 step attenuator, and outside of what I can order from the website, some teflon tube sockets, an IEC 60320 C17/C18 coupler for the power cord, and some tubes.

This is all based on my preferences though; on what sound you want, the kind of music you listen to, and what works well with others and what works well within your budget (but do the research yourself as your ears might be different from my tin-ears).
 
Far from an expert here. I built a dynakit ST-35 amp, and a VTA SP8 preamp, both from tubes4hifi. They drop ship the ST-35 from dynakit, Roy at tubes4hifi did have a slightly better deal with tubes included.

If you are at my level of ability. I think the kits from tubes4hifi are a good idea. They have a forum, Bob Latino and Roy Mottram are very responsive on the forum and via email. Lots of support, and if the worst happens, you can send your project back and they will fix it.

I run the 17wpc ST-35 with a pair of 92db 8" full range MLTLs. Plenty of volume, great sound. I am sure your Klipschs will work fine in a bedroom with a ST-70. Good luck.
 
The stereo 70 has its faults and purchasing a kit especially the one mentioned is not the way to go. I would purchase a Stereo 70 off ebay to start with. Then purchase a driver board from Geek. After that is installed and running then purchase a power supply board from triode. You will have far better sound and performance than the driver board with three 12AT7's on it. I can comment because I have tried that driver board in the past. Now, KT88's can and do run on a stock 70 with a bias circuit change. Mine will run KT88's, 6BG6GA's, EL34's and Russian 6n3cE's. Some will try to make you believe that you have to update the power transformer in order to run the 6SN7/6sl7 driver board and or KT88's in the amp. The truth is the amplifier was designed to daisy chain a Dynaco preamp or other that is pulling its B+ and heater voltage off the 70. That is what the octal sockets on the front of the amp are for.
 
You need to remember that doubling power only gains you 3 db when considering amplifier power.

The 70 when bought right is a good value after tweeking it. The mono block 125 is alot more money. I haven't heard one but do own a pair of mono block Quicksilver amps that I have put up against my modified Dynaco Stereo 70's that I have owned in the past and currently own. The 70 will and does hold its own against the mono block amps. I cannot say the same for the 35.
 
After re reading this thread is sound like an advertisement for Tubes4hifi.com

In my opinion I think they are in it just to sell their product. The information they like to give is slanted toward their product. They push you toward a new power transformer telling you that the original will not run KT88's or will not run additional driver tubes and this is false. The Dynaco was designed to piggy back a preamp off the front and not using the preamp opens the door to running different tubes. My 70 runs KT88's and 4) 6SL7's in the driver board and its still running. On a stock transformer still.

Their driver board is different than the original board and sounds better a slight step up. There are other boards out there that sound a heck of a lot better for the money.

Take the money you would have spent on one of their overpriced pieces and purchase a stock Dynaco and mod it or purchase a pair of Quicksilvers or citations.
 
RE Latino st-70 kit

I'll jump in here and say that I built the exact amp you asked about, Bob Latino ST -70 with both cap upgrades and high gain board (12at7's), earlier this year. I can recommend it as a great first build, the detailed instructions and support from Bob are second to none. I'm running kt-88's, cv4002 in the outer 2 sockets and an Amperex France 12at7 in the centre. I have found I do need a pre-amp ( I'm using an Aikido) when using my I-pod as a source. It has enough gain running straight from a cd player but still sounds better with the pre amp in between. I feel that the big bonus with buying a new kit is that it IS new.. no 40 year old transformers, tube sockets etc.. all the "upgrade" work has already been done, if you take your time and build it right you're guaranteed it will sound good. I'm sure Bob will sell you a kit minus driver board if you feel other driver boards are better. One last thought: add up all the time and expense to restore an original, 40 year old amp.. and it still won't look as nice as a new one with stainless steel chassis. Just my opinion of course and I'm sure others won't agree. I hope this helps, best regards and good luck.
 
ST-35

Check out diytube.com :: Index

Shannon should still have some boards available...

Here's my ST-35 with tesla tubes.
n659180021_1579934_3974.jpg
 
I did a KEGGER ST-70 clone PCB and I've been playing with an assortment of iron and output tubes.
The little 6P3S are the least expensive and worked great at 360V with little 8k-8 30watt iron triode more and 6.6k hammond 40 watt UL and Triode mode.
I bumped the power to 475VB+ and tried 6P3S-E 5881 wafer bases, UL and triode mode in 40 and 60 watt 6.6k hammonds, then Svet 6550=C=, followed by EL34's and KT88's.
I've been listening to the Russian 5881 wafer bases for a couple weeks in triode mode with the 40 watt hammonds and found it to be very respectable for the low cost of the 5881's. All tube/transformer combinations sounded better than SS, some were better than others. ( 5881 and 6550 were my favorites in triode mode, 40 or 60 watt 6.6k outputs)
With my speakers and listening room, triode connected is preferred for the fullness of sound, UL sounded a little hollow.
The stock ST70's were weak on coupling caps and power supply, each can be addressed. A truth in advertising was done and revealed that the Stock St70 was only about 18watts RMS/channel.
The modern driver boards with LTP design are a huge sonic improvement, adding additional filtering for the B+ helps to sustain the low end, larger PT current capacity also helps and runs cooler and can boost the true output power!
The bottom line is what do you want to do? Buy a ST70 and dive in a play with the magical upgrade combinations or buy a finished design or kit? Brew your own? You can't go wrong, just take the first step.....
 
The current ST70 kits with improved driver PCB's and power supplies are very good. The original design was lacking as a compromise on cost, but can be improved, overall an easy project. The new 120 would be the way to go for a larger amp, looks like an easy build.
I prefer DIY designs, currently working on a 6JT6 output tube PP amp PCB. I can find the tubes for under $2 each in the 17 volt heater flavor, at 17watts I should be able to squeeze 30watts/channel from them. My current project was a 6LU8 in PP and with Bogen iron a very nice amp. 6LU8's are only 14 watt tubes. Another novar or Magnovar tube is the 6GB5, 13GB5 and 18GB5 European sweep tube. With a top cap and a couple jumpers it can be used. This new design is based on the same mounting locations as the 6L6 based amp that was finished last year with the option of having the slow start damper tube on PCB instead of off PCB. I removed the diodes and first filter cap that would feed the choke from the PCB.
The bottom line is just to get started, it beats watching TV most of the time and it grows on you. It is a worthy challenge up to your creativity.
 

Attachments

  • 9.2 fired_up8.jpg
    9.2 fired_up8.jpg
    362.5 KB · Views: 597
  • REV-C.png
    REV-C.png
    102.6 KB · Views: 598
  • spud on top.jpg
    spud on top.jpg
    661.8 KB · Views: 589
  • spud on bottom.jpg
    spud on bottom.jpg
    712.5 KB · Views: 582
The original power transformer was lacking. It would run quite hot and with tube rectifiers you can not use large caps to power the B+. The output iron is very much the opposite, still very cherished today. A set of output iron will run around $180 -$200 comparable to the cost of a set of 40-50 watt Hammonds.
I prefer 5K-6.6K Raa iron, a little more class A operation.
 
The stock ST70's were weak on coupling caps and power supply, each can be addressed. A truth in advertising was done and revealed that the Stock St70 was only about 18watts RMS/channel.
I disagree. With new electrolytic caps and not very old tubes, I've had no trouble getting my 1961 build dynakit ST70 to put out >17 VACav into two 8 ohm resistors, or into 8 ohm speakers before I owned the resistors. This is on music, using a radio as an input. Of course music is not continuous RMS, but the voltage readings were seconds long, not just peak values. The meters were various over the years, starting with Radio Shack 20kohm/volt junk and ending with the Simpson 260 200kohm/volt one I;ve owned since 1986. (When it had new caps and won't put out >17vac, I bought new output tubes). Lastest re-e-cap and re-power-tube was 2012.
I wouldn't worry too much about running an original ST70 power transformer hot. I ran it 4-6 hours a night and 15 hours on some weekend days in a house in Houston, TX, for a decade 1970-1980. For much of that time my house was not air conditioned, and when I did use AC I've never pulled the house temperature much below 75 deg F. My ST70 sat on the floor, and only in 2012 did I notice it was designed for airflow through the bottom slots and install replacement rubber bumpers on the bottom to get it up off the floor. The only problem at that temperature, the choke melted out a lot of wax onto the metal plate. But the choke still works fine, as do the original transformers sockets etc. I have replaced some high value resistors with metal film for lower hiss, and the paper plate caps with plastic. I never had an actual cap failure, just read a lot of warnings. The original 7199 tubes are in it, and it does sound a little fuzzier (1% distortion remember) on grand piano than a Peavey CS800s at about 1.5 Vac levels.
 
Last edited:
There was a page printed in one of the magazines in response to the Federal Trade Commission on actual output power being rated to continuous RMS output power. I looked for the PDF on my old box but did not find it. Dynaco sponsored/ printed this page. It stated the continuous output power of the ST70 was ~18watts RMS. If anyone has a copy of this please post it.
This was during the rating wars where some manufactures would claim output power based on peak instantaneous power which inflated their capability.
The stock power transformer that I have did run hot, it failed the 3 second test which would indicate temps over 130F. The insulation is time and temp sensitive, the longer at high temperatures the shorter the life which pertains to most organic compounds. I prefer to keep the iron under 120F, electrolytic's don't like to be baked either... Others have stated that they do not mind the hotter temps on their iron, and that is their and your choice to do so. The ST 70 does respond favorably to a higher capacity power transformer with a larger cap bank on B+. It also responds well to KT88 and 6550=C= tubes where output feedback can be reduced especially when phase splitter uses larger coupling caps to improve the low end. It is a great little amp to play with.
 
i agree with roline, tube amps have lower power at lower frequencies because of output transformer limitations...therefore a tube amp rated for 35 watts at 1khz does not translate to 35watts at 20hz, it goes very much lower to about half....

since the FTC rulings promulgated in 1972, nobody bothered to revisit the power ratings to conform with the new rule...
 
Maybe 52 years on one power transformer is not enough. But there are not too many consumer products made now that will last even 5 years, however hot they are. I have had to replace electrolytic caps in the ST70 every 6-8 years when I used it >2000 hours a year, for low power. The last B+ cap I got 1 hour service life out of, and 20 years storage between installation (1982) and finding new non-Soviet output tubes (2012). Leaked the the slime out and blew the fuse the second night.
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.