John referred to as.
“Acquired this Pioneer amp I’ve purchased. Not sounding too good. Are you able to have a look?”
Yeah, why not?
It is Pioneer SA-6200 , relationship from round 1974. It is described as a medium energy versatile amplifier.
Powering up and it’s totally distorted on the correct channel.
It is clearly by no means been aside earlier than. It is filled with mud inside. A very good signal, means it hasn’t been bought at!
I clear up the pots and switches as a matter in fact, however the fault is definitely within the energy amp.
It is the same old 70’s push pull single rail association. AC coupled to the audio system.
Checking some voltages, and one thing’s very amiss on the enter stage. The voltages on the enter present mirror, Q1 & Q5 are very fallacious.
Positive sufficient C1 has failed, and is nearly quick circuit.
So it is duly evicted. Appears like an electrolytic, would not it? Nicely, it is not. It is made by Sanyo, and is, in actual fact, a tantalum capacitor. Once they’re of this age, they’re extra evil than the electrolytic!
It is rated at 0.47uF at 25V. I have not bought any, so I’ve substituted a 1u 63V poly. It will out-live me. I’ve modified it is best mate on the opposite channel too.
Speaking of capacitors… many of the electrolytics on the amp are in poor form too.. many bodily leaking and crusty. Let’s change them whereas we’re in there …
The re-capped board is fitted again in, and examined. Sounds good 🙂 Making about 14.5 watts RMS into eight ohms. It is speculated to be 15. Close to sufficient after 44 years 😉
The amp is buttoned again up, and given a soak testing with a little bit of Emerson, Lake and Palmer.
One attention-grabbing factor to notice, is the amp has two phono inputs. One doubles up as a mic enter. Each the inputs feed the RIAA equaliser, so your mic additionally has the RIAA EQ curve utilized! Ah nicely…