Thursday, March 3, 2016

Update my Dynaco SCA-80Q

Dynaco SCA 80Q
Some time ago I wrote about doing some updates to this 45 year old stereo integrated amplifier that I built from a kit in the mid seventies. The Dynaco SCA80Q appealed to me at the time because it was a low cost solution to satisfying sound from a good quality amplifier. I used it exclusively for about 10 years and eventually like anything old it found it`s way to the basement where it was turned on only occasionally through the years.

Last year I thought, heck lets bring the old amp to the cottage. At least there we can enjoy the sound of this antique treasure every day, Well, it was fine for a few weeks but its age started to show and show it did!  A mild, unobtrusive hum slowly developed into a loud and annoying one. I thought it might be the pots and switches and perhaps they needed a little cleaning spray to fix them but I soon discovered that it was much more than that.

I did a little research online and discovered that the old capacitors had seen their days. As mentioned in a previous post I bought a couple of capacitor kits and promised myself that through the winter months I would install them. The kits came in the mail and I must admit they sat around for a while. I had to summon up the nerve to tackle this project. And I did, finally!

The first one I worked on was the C9, the easiest.
C9 capacitor
It was fairly simple procedure and all that is required was the ability to use a soldering gun and to read instructions. This is what the C9 looked like and below is the replacement from a slightly different angle So, basically I stepped up from a 5000 mfd capacitor to three 3300s.
Three capacitors in dynamite formation
Next was the C11. It was more complicated and I admit it was not all that much fun. It meant assembling a circuit board. Here is the C11 completed and mounted. The result was that the hum was gone, totally. Certainly the failing capacitors were the problem.
C11 capacitors on circuit board
There were two other capacitors, the C7s, that needed addressing. It was an optional project. I could have left them in but eventually they would need replacing. I did a voltage test and I found that they were fine but they are 45 years old and wanting to be proactive I decided to change them out. 

They are the speaker capacitors, one for each channel. The C7s as they are called, were changed out for two sets of capacitors in dynamite formation. See the next photo.
2 C7 capacitors sets
The C7 kit is typically for the Stereo 120, a more powerful Dynaco amp. So, I had to interpret the instructions for my amplifier. Not complicated since there are fewer wires to connect. 

The end result is that the amplifier definitely sounds different. There is significantly more bass and a cleaner better defined sound overall. At its improved state it certainly would not be a match for today's audio technology after all it is 45 years old. But it is still very good.

The chassis was cleaned with compressed air, the solder joints were inspected and one or two were 
re-soldered. The oak case, an option at the time, has been refinished. 

One or two other issues have yet to be addressed. First, the pots are very, very stiff and a DeOxit cleaning is in order. I was getting a little audio distortion on one side even before changing out the C7s and banging the pots a little fixed that but they do need a thorough cleaning. I ordered some DeOxit locally and will treat the switches and pots in the next day or two. The front plate also needs a good cleaning. 

Chassis is cleaned, caps replaced
All in all, a great project. For sentimental reasons I wanted to get my SCA80Q renewed so that I could enjoy it in the years to come. I am very pleased with the outcome.