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My salvaged Dyna 70 - the first pictures.

Moon_Man

Moon_Man

The wheel is turning and you can't slow it down.
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Salvaged this Dynakit Stereo 70 from a certain trip to the dump along with a Dyna preamp, an AR-Xa turntable and a Voice of Music tuner. This is my first tube amp, so any insight as to what you see here would be invaluable.

First, as it was found:

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Now with the cage off. Lots of dust and dirt. Probably spend quite a few years in a basement, but it couldn't have been a damp basement as there is very little rust and corrosion.

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A close up of the circuit board assembly. Nasty:

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After the judicious use of compressed air and a soft bristle brush, a much better looking specimen.

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A close up of the cleaned up circuit board. Note the "Black Cat" caps and Dynaco tubes - do these help to determine the vintage of this unit?

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The underside. Is that the dreaded selenium rectifier in the center of the picture? Also - has the choke been replaced?

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Close up of tubes.

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And finally, the test. "We have ignition".

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Left it turned on for less than a minute, but I suppose I'll will actually see if she still sings at some point. There is obviously a lot of work in her future, but first I'll need to educate myself.

These finds have re-prioritized my fix-it list, with the amp, pre and tt now at the top (well, behind my already apart Timewindows).

Whadda ya think??

Tom
 
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Well, there's a couple hundred bucks worth of Mullard tubes there, and the leads look like they might be the desirable cloth ones.
The ST-70 is a well worked amplifier here and there will be plenty of help to guide to you here.

You did great!!
 
sweet, hook up some cheap speakers and a cd player and give it a listen for an hour or two.
 
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Whoa! Andy, Fern, are you telling me that I can assume that the tubes are good to go?
 
My priority list:

Get rid of the selenium rectifier.

Replace the can cap

Replace bias supply caps and resistors.

Replace driver board components.

Don't run it too long before replacing the parts that can take out trannies.
 
Check the date codes on the transformers. That should give you a reasonable clue as to when it was built. Nice score, especially with all the original tubes.
 
Moon_Man said:
Whoa! Andy, Fern, are you telling me that I can assume that the tubes are good to go?
Click to expand...

Most likely. I'd say about less than 1% of the tubes I find and test are trash and probably 50% are strong enough to sell easily. The rest are certainly solid enough to use as daily drivers or use as tubes in amps I sell.

If those are brown base Mullard EL34s that test strong, they're worth a pretty penny themselves.
 
I have to say from the pics it doesn't look as if it was used much. The board usually discolors from heat and I don't see any sign. (at least from pics). Tubes might be near perfect. You might want to replace PS cap (electrolyte tends to dry out).
 
I'd say that one deserves to be put back bone stock (except for caps, and other bad things underneath). Have you listened to it yet? Sometimes kit amps didn't work because the builder goofed. I think a lot of these found there way to top closet shelves etc... That may be what you have. I've had two so far, an AA151, and a KX200. The 200 would work, but sound terrible, the 151 wouldn't have had any B+.
 
a thought.. hollowing out the old resistors and caps. and useing them as shells to hide the new smaller parts inside.. so it still looks all origional.
 
Those plastic shell caps are quite difficult to do that with. Its two shells that are sort of glued together. If you get lucky and manage to crack them along the seam, it might be possible to pack a modern small cap inside but I've not had much luck getting those to crack in the right spot. Usually they just shatter if they weren't already swelling up and cracking on their own. Resistors I wouldnt even try that with. If the ones topside need to be replaced and original appearance is a concern, some Allen Bradley carbon comp resistors would look exactly like whats there now. For all that, A-B might be whats there now.
 
Nice to see original "Dynaco" 7199s. As others have said, this looks totally original, including the choke.

You did hook up some speakers before powering up, right?

To add to the to-do list, I would consider replacing the two slide switches, or at least give them a squirt with switch cleaner and work them to and fro.

gadget73, please could you post info on how to check the date code on the transformers? On this, I've just seen this thread here: http://dynacotubeaudio.forumotion.c...te-of-manufacture?highlight=date+manufactured
 
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There should be a string or two of numbers on the transformer. One is typically the part number, the other should be a 6 or 7 digit string that has the transformer manufacturer's EIA code and the date code. See yonder list for how to read it:

http://www.triodeel.com/eiacode.htm

The larger capacitors also should have the manufacturer and date codes on them. Tubes will too, but being Mullards they use a different date code arrangement that I do not know.
 
jaymanaa said:
I'd say that one deserves to be put back bone stock (except for caps, and other bad things underneath). Have you listened to it yet? Sometimes kit amps didn't work because the builder goofed. I think a lot of these found there way to top closet shelves etc... That may be what you have. I've had two so far, an AA151, and a KX200. The 200 would work, but sound terrible, the 151 wouldn't have had any B+.
Click to expand...

Not stock. The driver board on the Stereo 70 is a gawdawful circuit. You're better off pulling the board, setting it aside along with the 7199s and storing it, and replacing the board with either a VTA or DIYTube driver board. That way you have the original circuit should you decide to sell it, but you won't have to suffer with the sub-par audio from the stock driver board.

-D
 
nj pheonix said:
I have to say from the pics it doesn't look as if it was used much. The board usually discolors from heat and I don't see any sign. (at least from pics). Tubes might be near perfect. You might want to replace PS cap (electrolyte tends to dry out).
Click to expand...

Even all the print on the components is almost factory fresh ... maybe change "not used much" to not used as all? It's a kit build, so maybe whoever built it never could get it going right and shuffled it off to the side ... waaaay off to the side ...

Kinda like mine ... winter's coming, so there's still hope I'll git er done ... <G>

Anyway ... the can cap and resistors at least. The clock is ticking on those when they leave the factory - doesn't matter if it's used or not. The new replacement cans have also got more beef to them ... the stockers were borderline when new. Those old carbon resistors are pretty, but I'd bet a read on a meter would put them all over the place for values as they soak up moisture and drift ...

And ya ... killer find. I got an old roof I got to cart down to the dump this week ... have to keep a close eye on what everybody else is tossing!
 
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My plan is to do all listen to it briefly to make sure it works and then to undertake repairs.

Gadget: I will check the date codes on the xformers and post.

nj: I agree, it doesn't look like it was used much.

aidyn: Not really that interested in bone stock, more getting a nice looking working unit, with possible upgrades, like a new board.

Dandy: only had it powered up for around 30 seconds, so I wasn't too worried about having a load on it.

Thanks for all your help. Keep the ideas coming!

Tom
 
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