PHILIPS 661 STEREO TEST AMPLIFIER – Actually this unit is not an original Test Equipment, but I make it became one. And, after see how useful it is, I decided to insert it at the site. The backbone of the unit is an old audio system made by Philips in late 70's. It was found at the junk, with food and other garbage. Since the original wood cabinet was irreparable, and the sound of the unit were really great, I took off the turntable and inserted it on an old 19" standard cabinet I had as spare. I use it for checking audio sources, to test speakers and many other things. I put a BNC inlet on the front panel, to ease the access to the input, since the back inputs are DIN type. Also I placed the output access on the front panel, to test speakers.
The audio power of this rig is not over 10W per channel, but the THD is very very low - believe me, under 0,01% at 10W!!! And the sound is very weighted, as I like, but have a particular brilliance only found in more (really much more) expensive sets. Every time I turn on this rig I impress myself with its sound. Actually the output is switchable between front and back. The front is free to be connected on speakers under test, and the back output is connected to my MIBRIO speakers set. The Phono input is connected to the front panel, as you can see below; the Tape input is connected to the PC audio output; the Tuner input is connected to the DELTA 105. When you insert a plug on the front outlet, the back outputs are disabled, end you can either use the front outputs to test speakers or to listen with earphones.
When I want to test audio sources, (DVDs, CDs, Tapes, MP3's, etc) I use the MIBRIO set and the front input; when I want to check speakers I use the front output and an audio generator on the front input, or music content from Tuner or Tape inputs. If you have an old audio amp stuck at the attic, give it a good job. It will reward you.
Here are the schematics of the 661 amplifier