Dynaco ST70 Original? Or not...

Well..... after hearing all of these responses, and knowing that I do not have the knowledge or skill to do this amplifier the justice and investment it deserves, I guess I will need to verify that the unit works, as least the power supply portion and make sure its salvageable and offer it up to someone who has the knowledge to bring this guy back to life. I purchased it hoping it would be an easy repair and you just needed to replace the tubes and viola! obviously I was mistaken!

James

It might help to post your location - there may be some local kindly AK'ers who are willing to work with you on doing some initial checks. As others have said, if you have an interest, it's a good amp to learn on and if you get it up and running, it's a nice sounding amp with a lot of options for modifications.

I upgraded my working ST-70 with a new driver board, so I have my original driver board available. If you want to give it a go, it's yours for the cost of shipping. One option would be to replace your unknown status board with mine, which will eliminate a lot of components as possible failure points and my 7199 sockets are fine, so you wouldn't have to clean/re-tension the ones on your board.

It will still require disconnecting (cutting or de-soldering) all the wires from your current board and being very careful to label them and note where they need to be re-soldered to my board. If you've never soldered before, you again may want to have someone who has there to help - or at least watch some videos and practice a bit before digging in. The can cap (silver cylindrical capacitor visible from the top of the unit) would still be a question, as well as there are a couple of caps underneath that would also possibly be bad. But you're down to a handful of components, and while aged, they may still be okay enough to determine functionality.

A local AK'er may also have some old tubes that could be used for a quick check versus your having to buy a whole set. Many of us have weaker old tubes that have been set aside as not good enough to use as daily drivers, but good enough to use for a functionality check.

If you can determine that all the transformers are good and it's working, you can then decide the path for restoration and possible mods/upgrades. While your chassis has rust issues and is dirty, if you can do some basic cleaning and stop any further rusting, it's just a cosmetic issue and you can determine whether that bothers you or not. if it's not going to be your long-term tube amp, you can use it as is and it's rough condition will just be a reminder that you brought a piece back from the scrap heap.

The point is, you may have some options if you don't want to give up on it just yet. Good luck and if you're interested in my driver board, just PM me.
 
I’m with captouch. Post your location and you might get a local AKers help. I believe captouch was involved with giving or receiving such help in his local, right cap? (I seem to remember a very cool thread in the Fisher forum with Fernando maybe?)

Don’t let anyone scare you away. The ST-70 is probably the easiest amp to cut your teeth on if you have any ambition at all. It’s a power amp only which makes the circuits simple. These came as kits and 10’s of thousands were sold to common folks who were able to build these units that are still being built as new kits 60 years later. If you are cost sensitive start by checking the transformers. Then make your decision.

Question: If you could get the help would you be interested to learn and do the work?
 
SAFETY FIRST if you don't have any electronic knowledge don't mess around with it ." What I hate about electricity , you can't see it coming "

Learn the hazards!!! And you will be fine.

Well..... after hearing all of these responses, and knowing that I do not have the knowledge or skill to do this amplifier the justice and investment it deserves, I guess I will need to verify that the unit works, as least the power supply portion and make sure its salvageable and offer it up to someone who has the knowledge to bring this guy back to life. I purchased it hoping it would be an easy repair and you just needed to replace the tubes and viola! obviously I was mistaken!

James

Safely working on these is easily done. It’s not rocket sience. These where sold as kits to people that where clueless and I am sure a lot of those builds are still working. I have one that was done as a kit and it’s original (pulled the selenium rect) and works great. As stated above this is the amp to learn on, just get the manual and jump in. Lots of peolple did back in the day and I don’t remember hearing about an outbreak of amplifiers murdering people in the 60’s and 70’s.
 
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I’m with captouch. Post your location and you might get a local AKers help. I believe captouch was involved with giving or receiving such help in his local, right cap? (I seem to remember a very cool thread in the Fisher forum with Fernando maybe?)

Don’t let anyone scare you away. The ST-70 is probably the easiest amp to cut your teeth on if you have any ambition at all. It’s a power amp only which makes the circuits simple. These came as kits and 10’s of thousands were sold to common folks who were able to build these units that are still being built as new kits 60 years later. If you are cost sensitive start by checking the transformers. Then make your decision.

Question: If you could get the help would you be interested to learn and do the work?

Ferninando and I have worked together on multiple projects - the KX-100 probably being the one you were thinking of. My ST-70 I did on my own using the VTA driver board.

I hope the OP gets some help and gets this up and running. A nice tube amp is part of the audio journey. . . :)
 
Ferninando and I have worked together on multiple projects - the KX-100 probably being the one you were thinking of. My ST-70 I did on my own using the VTA driver board.

I hope the OP gets some help and gets this up and running. A nice tube amp is part of the audio journey. . . :)

Yes the KX-100 thread was it. I copied your IBAM. Turned out nice. Thanks. If I can do it than so can others. The Dynaco will be easy.
 
why spend hours or days verifying/contradicting various theories over a 60YO board
when there are replacements for $15 shipped (ebay), and for now a
brand new chassis for $50.

what's your time worth, or more importantly, how long and hard will you
work before you get to listen to this, assuming you have lots of $$$
to pad the time and effort.


I would say that THE ONLY useful piece in this amplifier is transformers. When they are tested good, pull them out and discard the rest. Get all new chassis and board and build all new amplifier using transformers you got.
 
Tempted to agree. The chassis is pretty rough. You can clean it up somewhat but the chrome is peeling off and its got a lot of pitting, it will never be a showpiece. The board I'm more indifferent to, but the lack of available 7199 tubes and the general misery of rebuilding those old boards would make me real tempted to buy a new, stock circuit board that runs some more available pentode/triode tube.
 
I disagree. It depends on your goals and level of commitment. I restored a Fisher KX-100 integrated tube amp that was so rusted it lost all stenciling. That’s cosmetic. After cleaning the rust and dirt away it wasn’t all that ugly. The guys on the Fisher forum encouraged me to save it as a “survivor”. I did and it’s my main rig now. I am so proud that I saved it. It sounds sweet and looks decent. The scars let it show it’s age which is not a bad thing.
 
My Pilot SA-260 and my Bogen DS-225 aren't show queens either, the chassis have some rust, the finish is damaged, etc. I cleaned them up and run them, but if I had a chance to buy a brand new chassis with perfect finish for under 150 bucks, I'd have probably done it.
 
I would say that THE ONLY useful piece in this amplifier is transformers. When they are tested good, pull them out and discard the rest. Get all new chassis and board and build all new amplifier using transformers you got.
That's pretty much where I am with my ST70, plus the chassis. But it would still be fun and worthwhile to begin by getting it working stock.
 
I agree on the flood comment. I once found a stereo 70 that was outside for quite some time that was basically in this same shape. That said, IF you can verify you have a useable set of transformers and do the work your self you should be able to justify the cost of getting it going.
 
I agree on the flood comment. I once found a stereo 70 that was outside for quite some time that was basically in this same shape. That said, IF you can verify you have a useable set of transformers and do the work your self you should be able to justify the cost of getting it going.
Yes, that's what I would do. As long as the three transformers are good, you're 3/4 of the way there. Buy a new chassis, driver board and any other parts needed to rebuild it. It's not hard, just time consuming but you'll end up with quite a prize.
 
I would say this an DIY amp project. It would cost way more for a tech to fix than the amp is worth , if it can be fixed at all. You can buy new Dynaco amps in kits or fully assembled and tested online . I have ST120 kit from Bob L. its nice I built it and I have $1500 in it . SAFETY FIRST if you don't have any electronic knowledge don't mess around with it ." What I hate about electricity , you can't see it coming "
A trained hand can feel it coming, observant people will notice hair standing up and that sweet itch in your fingers before it bites ya. I also work with neon bulbs attached to any probe they will light up when near high voltage.
 
those were actually sold years ago as a non-contact tester for the CRT high voltage supply in television sets. I made one from a chopstick from the local Chinese place and an NE-2 but I have a commercially made one that is essentially the same thing.
 
I know it's an old thread, I have been doing this since 1975 (or so) and every time I got bit, I could never sense it coming, but I only got bit across the hand / forearm, (and only less than 500v) as I have always used the one hand rule.
 
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