I'm Nicola from Italy. More than 40 years ago my grampa bought a fully equipped stereo system with radio, record and audio reel players and (above all!) a Dynakit Stereo 70 with a PAS-2 pre-amplifier and two "Esquire" speakers from ElectroVoice.
About ten years ago I retrieved speakers, ST-70 and PAS-2 and started using them. I had no experience with electronic jobs, so I simply cleaned and powered them up. I used them for ten years.
Last winter the ST-70 began to emit a 120Hz hum. I searched solutions on the internet and replaced the can capacitor. The new quad-cap is the only piece changed in over 40 years, everything else is completely original.
I know that I could make a lot of improvements to my Dynakit but I'm not so expert with electronics and I believe that is better not to touch an old thing if it works!
By the way, some days ago my ST-70 started to make a singolar short noise on the left channel only. Each time I switch it on, after 2 or 3 minutes I can hear this noise once. Apart from that, it works well.
I've seen the quick troubleshooting guide on this forum, especially point 13: "One channel cuts out completely or drops in volume after time". I don't know if my problem is connected to that, so I recorded the noise from my ST-70 left channel to have your opinion.
Waveform screenshot: img38.imageshack.us/img38/1279/st70noise.png
The noise sounds like when you power up something for a few seconds, then you turn it down. So it has an initial peak and a final peak. Between these two peaks, there are 2-4 seconds of "almost" silence: normally the amplifier has a little operating noise. Between the peaks, the operating noise is a bit louder.
In order to be sure that this noise depends only on the amplifier, I tested it with no input (rca disconnected) and with different speakers. On more recent speakers, peaks are less loud, but still exist.
The only coupling of the ST-70 with other pieces is the power cable coming from the PAS-2 output.
Thanks in advance for your opinion and for this forum, I'm new here but I feel this is a friendly community!
Last edited by Nicola on Tue Dec 13, 2011 7:57 am; edited 3 times in total