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ST-70 acquisition, now what?

Don't sacrifice safety for originality. If at all in doubt, replace the power cord. It is only wire and unlike Fisher power cords with the molded on emblem, there is nothing special about the original.

Shelly_D
 
dmag said:
For simplicity sake, you might completely disassemble and clean the parts, buy a new can cap and wire and reassemble according to the original dynaco instructions. Dynaco's manual was truly idiotproof. Then you can mod or not.
Click to expand...

this in fact is basically what I will be doing but is the manual stupidhead proof? LOL thanx dmag and I have begun the de-soldering chore.

Lavane said:
Personally, I would buy a new board kit. You will get better sockets and a much better made board. Those phenolic boards are like old dried out Graham crackers. Brittle and weak.
Click to expand...

the board is my biggest quandary and I have seen a couple resources for a duplication of original design using the 7199 tubes. still pondering this as I complete the de-soldering activity.

gadget73 said:
Ditch the can cap. Replace the ones in the cardboard tubes too. Those old style components aren't really obtainable anymore, and frankly they do not age well so I wouldn't go seeking NOS ones either. On some level you're going to have to accept that this will not look how it did in 1965 or whenever it was made.

If you do want it to look like it did, you're probably going to have something that is really only suitable for shelf decoration. I wouldn't be inclined to run an all-original amp on a regular basis for fear of it having a meltdown.

The residue on the tube sockets is probably solder flux. If it chips off with a little bit of poking and is an amber sort of color, thats what it is.
Click to expand...

I will absolutely be replacing the cap can, and no real interest in NOS for these types of things. Definitely will go with quality replacements for all caps and resistors. I would love to find NOS switches if there is a known resource for them. I will take a close look at the residue but not really amber, more a chalky look.

shelly_d said:
Don't sacrifice safety for originality. If at all in doubt, replace the power cord. It is only wire and unlike Fisher power cords with the molded on emblem, there is nothing special about the original.

Shelly_D
Click to expand...

Shelly I appreciate the concern and I share this concern. The cord is solid, no evidence of brittle, cracking, exposed etc.... but I will likely go with a more substantial grounded replacement.

Once I have completed the dis-assembly of all components I will post a few more pics and finalize parts order.

Geoff
 
+1 on replacing the board with a 6U8 type. Even thou you can find old 7199's they are most likely heavily used and near the end of their sonic life.

Besides getting a new board will solve a number of "ills" You can order an assembled board from VTA.

http://www.tubes4hifi.com/ST70.htm

Don't get the 6SN7 board unless you are willing to do more modifications then just drop in the new board.
 
airtime said:
+1 on replacing the board with a 6U8 type. Even thou you can find old 7199's they are most likely heavily used and near the end of their sonic life.

Besides getting a new board will solve a number of "ills" You can order an assembled board from VTA.

http://www.tubes4hifi.com/ST70.htm

Don't get the 6SN7 board unless you are willing to do more modifications then just drop in the new board.
Click to expand...

If I'm not mistaken the 2 VTA boards are the same as far as the install.

I never heard the VTA in a 70, only a 120.
I prefer the stock board in a 70 to a VTA in a 120.
Honestly different output tubes and transformers. So not really apples to apples.
Just an observation
 
nj pheonix said:
I never heard the VTA in a 70, only a 120.
I prefer the stock board in a 70 to a VTA in a 120.
Click to expand...

I've used the stock board in an original 70 and a Curcio replacement, then the upgrade board. I prefer the simple replacement board over the balls out upgrades personally.

One thing that is VERY nice with the VTA board is you can use the 12BH7. A much better sounding tube than the 12AU7. I tried rolling a dozen or so 12AU types and always came back the 12BH7.
 
I (also after extensive rolling) also preferred the 12BH7s in that board.
The long black plate RCAs specifically!
 
nj pheonix said:
I (also after extensive rolling) also preferred the 12BH7s in that board.
The long black plate RCAs specifically!
Click to expand...
I wound up with two OS long plate 12BH7's and a NOS Tungsol E80CC in the center. I tried the 12BH7 in the center, along with many others, and the E80CC long plate won out.
 
Lavane said:
I wound up with two OS long plate 12BH7's and a NOS Tungsol E80CC in the center. I tried the 12BH7 in the center, along with many others, and the E80CC long plate won out.
Click to expand...
Keg recommended those to me. I tried a few variants. Came back to the BH7s. I also swapped in the octal board. I had (have) a lot of respect for that amp . I did move it. One other thing Keg said to me . Its not for everyone.
While i never had them both at the same time, (memory is a funny thing) I'm more satisfied with the (basically) bone stock 70. (again different iron, output tubes, . Except for basic topology, a different amp.
 
nj pheonix said:
Keg recommended those to me. I tried a few variants. Came back to the BH7s. I also swapped in the octal board. I had (have) a lot of respect for that amp . I did move it. One other thing Keg said to me . Its not for everyone.
While i never had them both at the same time, (memory is a funny thing) I'm more satisfied with the (basically) bone stock 70. (again different iron, output tubes, . Except for basic topology, a different amp.
Click to expand...
I've had a number of the original ST-70's during the early years of ebay. Yeah, when you could buy a Dynaco for $100 or so. At that time I did try a number of the available replacement boards as well as the "supped up super modded" version boards. I never cared for the big high end boards and always came back to the BASIC (non 7199) replacement boards.
 
@nj pheonix Keg suggested them to me also. But me being me I had to try everything else first. Then I tried both the Philips and Tungsol E80CC's. The reason I went with the Tungsol is it has this slight darkness to it. With less busy passages there is what sounds like (to me), a quiet space around the instruments. I guess I just hear more detail. The ECC99's sounded nice too, but had a fatter sound that was a bit much with some music. I still need to try a 6SN7 with an adaptor though, being a fan of the 6J5.
 
alright....give

love the banter here on tube rolling. I have read on numerous occasion of this form of entertainment but never have I done it. I have a question on this though. It seems as though the consensus is the classic board with 12AU7 or like is favored and no mention of the "octal" board using the 6SN7 tubes. Don Sachs (McShane tech) told me in no uncertain terms to just get the octal board. I am going to get one or the other and wonder if you guys have any thoughts on this comparison.

Geoff
 
I think the consensus was make it work with the stock board and see what you think.
I think you could start a whole new thread on after market driver boards (I'm sure it's been done already)
I'm also reasonably sure there's no consensus on which after market board is best. (Purely subjective)
As you saw in the brief friendly exchange even with the same after market board, you won't get consensus on tube choices.
It will come down to your ears.
You need a starting point.
You have to address the PS anyway.
Fix it stock. Listen to it.
If you think its not what you want it to be, have at it.
Most importantly, enjoy the journey.
 
nj pheonix said:
I think the consensus was make it work with the stock board and see what you think.
I think you could start a whole new thread on after market driver boards (I'm sure it's been done already)
I'm also reasonably sure there's no consensus on which after market board is best. (Purely subjective)
As you saw in the brief friendly exchange even with the same after market board, you won't get consensus on tube choices.
It will come down to your ears.
You need a starting point.
You have to address the PS anyway.
Fix it stock. Listen to it.
If you think its not what you want it to be, have at it.
Most importantly, enjoy the journey.
Click to expand...
EXACTLY and well put.

Just get it in good working order in "near stock" condition. THEN mod it up with Octal boards and what ever. I think you're going to find a few of those high end mods to be very taste specific . And more times than not, not what you were looking for. Come to think of it that was my down fall with my first Dynaco. I went hog wild WAY to early and ended up selling the thing in frustration. A good working Dynaco is a good sounding amp.
 
stupidhead said:
I am a bit torn on this angle. I fully understand the equation of old tube 7199 becoming harder and harder to find. However it is far from unobtainium as some suggest, more that it commands a premium due to availability. The actual struggle I am really having is whether to replace the board at all? My soldering skills and equipment are of a novice level, and I am dubious of reworking the original board myself for fear of the traces lifting or otherwise mucking it up as I have read repeatedly. Seems replacing board (oem design) with a more recent production/materials/pre-populated is the easiest approach, but does veer a bit away from oem? I would love to find some like minded AKer local to me who has the skills needed to rework the original board, and as Ferninando said



So again, if anyone local to me (Southern NH) is of a mind to give me some assistance with this, I believe I would like to keep the oem board and rework with fresh components. I would be happy to drive to or host an afternoon of board rework.

As promised, a few more pics of the disassembled guts of this thing, first the transformers.

View attachment 1002166

and again, all I have done is extract from chassis (desolder not cut wires) and of course I tagged and recorded all leads. A bit of mild cleaning and a coat of wax leaves these in very presentable condition and I am not even considering repaint. I much rather the romance (and appearance) of original, a little beat up as opposed to a perfect appearing repainted anything.

The choke shows no evidence of overheating and I have done virtually no cleaning prior to taking this picture.

View attachment 1002168

and I have seen a 65 on this and all transformers as well. Safe bet it was produced in '65 yes?

Then this pile of pieces/parts is all in decent shape, depending on final decision of board approach will dictate just how much of this gets undone. I will get new (oem style) switches for power and m/s. The fuse holder is not oem I am told so will effort an oem style (or original) if available. I have not taken close ups but a question about the tube sockets. On one side it appears as there is some crusty remnants on the top surface of the sockets. Not a lot, but definitely there. The other side pair is clean to the original surface and no evidence of crustiness. In the below pic the bottom pair of sockets is the clean pair and the upper shows the crustiness. I will get some better pics of this later but thought I would mention now.

View attachment 1002169

Then there is the cap can. Again I did not take close up but there is definite evidence of crusty leakage coming out of the bottom of this thing. Forget the romance, just replace with a new version unless someone has other ideas?
My real quandary is about the cord. I suspect I can clean this original one and reuse, but I am leaning towards replacing (and grounding) cord with something a bit more substantial. Where do I draw the line for keeping it original?

View attachment 1002170


Folks, I greatly appreciate the input here.

Geoff
Click to expand...
About the tube sockets, I would replace them all since you have it apart. Why take a chance of blowing a good (expensive) power tube. I used the Japanese , silver plated ones from Angela Instr. The 7199s are not as critical but.......
The power cable should be a 3-wire in my opinion. Why take the chance that a high voltage lead could detach and contact the chassis. That would put 425v on the metal chassis. Just be sure to plug all your 3-wire plugs into the same outlet (strip) so the Earths are all together.
 
nj pheonix said:
I think the consensus was make it work with the stock board and see what you think.
I think you could start a whole new thread on after market driver boards (I'm sure it's been done already)
I'm also reasonably sure there's no consensus on which after market board is best. (Purely subjective)
As you saw in the brief friendly exchange even with the same after market board, you won't get consensus on tube choices.
It will come down to your ears.
You need a starting point.
You have to address the PS anyway.
Fix it stock. Listen to it.
If you think its not what you want it to be, have at it.
Most importantly, enjoy the journey.
Click to expand...
I like my VTA amp. If an original Dynaco fell into my lap I would rebuild it stock with all new caps and resistors. But, I think I would use a new stock configured board. Better sockets and better made board. With the VTA ST70 I built I used the 12au7 board. Many different tubes can be tried and with adaptors you can still use 6SN7 octals. I completely went through a FM3 tuner and those old boards were a pain to work with. The traces were fragile and so were the boards themselves. If the single all in one board available wasn't so expensive I would have used it.
 
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