COMPLETE RESTORATION SERVICE----DYNA STEREO 70

MUST READ---MUST READ---MUST READ---C'MON NOW, READ THIS RIGHT OFF!!!!..This listing is for the service required to enable nasty, tired old Stereo 70's to become like new and robust......Like Charleton Heston when he beat up all of those guys at the well in "The Ten Commandments"....you know, full of life and sex appeal. So if you have a Stereo 70, plan to get one, or just desire to know more, Read on:

So you have a Dynaco Stereo 70. When Uncle Otis went to his reward, he left it in his closet.....or Grandfather Wilson gave it to you.....or you found it at a garage sale (ha ha...fat chance of that). Whichever.....Bottom line is that it came to you, you have it now. You suspect that it is a very cool piece and that you should take it seriously. Very good, you are correct on that score. You suspect that it may need service and in spite of all the temptation to do so, you refrain from even plugging it in and wish to refer it on for service first. OK...I know that is too much to ask. Actually, you did plug it in but it didn't sound quite right, so you turned it off again. Very good, don't do that again. The fact is that you have one of the coolest tube amps ever put out, but it needs full restoration before you should use it. But where in the world can this be done? Do not go to Joe's TV. Do not go to Circuit City. Do not go to Acme VCR and Stereo Service....Sorry pal, but these people are all in the business of doing something else--They are not on the Stereo 70 wavelength. No, this can only be done by a specialist....and that would be me.

You wonder to yourself, "but if I turn it on and it sounds ok, isn't it just OK?.......The answer is no....it isn't. I know that would be a lot of fun, but you know the real world. You always have to do something to get what you want. At least in this case, it all makes a lot of sense that after 30 years, the unit would need some help with its stability and also with performance. The good news is that the normal restoration on one of these is very straightforward, and always worth the cost. When complete, the unit tends to be very reliable, and the sound is superb......"So just what is a normal restoration anyway?"......Well, I'll tell you in a moment, but first, here is another "before" picture.

Now, to the standard restoration. We will save tube considerations until later as we are now dealing with bringing the chassis itself back into line. On your beloved Dyna, the most important things sitting on that chassis are the transformers. Fortunately, they rarely go out, and this is good, they are not readily available. The most common problems found on Stereo 70's are not surprising.....the caps go bad, the sockets become oxidized, and you will usually find a number of bad solder joints. Many of them were kits after all, and they are often 35 years old. The best thing about this entire situation is its consistency. If you restore a 70 properly, and if you then put good tubes in it, then it is dynamite....a wonderfully warm and engaging tube amp.

So, long story short, we replace the filter caps, and the coupling caps. We remove the selenium rectifier in the bias supply and replace it with silicon, and then replace the caps in the bias supply. When that is done, we clean and deoxidize the tube sockets and we inspect the unit carefully for bad solder joints and fix any that we can find. We use the dremel tool to buff off the input connectors and the output terminals. When this is done, they usually fire right up since we have replaced all of the stuff that is prone to giving us trouble. Of course you don't feel that you are home free until you have set the bias and have burned the machine in for an hour or two and have found that the bias is stable, and that the baby sounds good. Once you have found it to be stable, you then have a machine which will perform beautifully for years.

This is not terribly tricky work, but I do not recommend it to the novice unless you have some bench skill already. It is very important that it is done slowly and carefully, and when the job is complete, it is very good to be able to monitor the current draw of the piece so you KNOW that it is right. The very last thing you wish to do is to foul up and eat a transformer. If you try it yourself and this happens, then don't come whining to me because I am warning you here and now to be careful. So there. The other matter which you must consider is that the filter cap, a 4 section baby has spotty availability. Some of the filter caps you can get are limited to 500 volts, and that is a touch close to the actual operating voltages. To avoid this, our method is to leave the 4 section cap in place because it looks right, and to glue an array of caps in the underside of the chassis to take its place. These have a resultant limit of 700 volts....much better. Take a look:

Now as to the tubes you should use. The best tubes are old....American, or British, or German.....and they are priced accordingly. Certain Russian tubes are not half bad, especially for what they cost. We never, never, never use Chinese tubes, having seen many go bad already. The rule of thumb is to evaluate the tubes you already have in the unit....and to go from there. In effect, you send the unit to me and I make tube recommendations for you. The price quoted for the Stereo 70 overhaul is everything except the tubes. If I find that you have unacceptable tubes, either I can get replacements for it or you can find them and send them to me. We must have the tubes to complete the overhaul, as we wish to set the bias and to confirm performance.

So there you have it. If you have a lovely Stereo 70 and wish for it to be back to its original performance, then you should send it in. If you have any questions, send them via email or call me at (512) 294-5635. If you have a lovely tube amp that isn't a Stereo 70, it is likely that its restoration would be similar to this. Get its brand name and model number, call and ask, and I will speak to that. Take it from me, if you have not carefully listened to one of these fine tube machines, they do have a wonderful sound and are exactly what you need. Thanks, Bill.