10-20-2014, 07:54 PM
I recently bought a Dynaco PAS-2 from ebay and began restoration. This unit had been modified to just be a phonograph preamp. I ordered a 100k ohm volume control with loudness tap, new polypropylene capacitors and metal film resistors plus a new modern function switch that is much smaller than the OEM switch which had been removed. I had to rewire the front controls to the circuit boards and then changed parts. I added two 12AX7A tubes from some used spares I had on hand. I used the small OD shielded audio cable material between the jackfield and the function switch. This helps eliminate cross-talk between high level signals and adjacent cables. Some old resistors are still present but will be changed later. A new power supply board and electrolytics will be installed where the filament filter capacitors are presently under the old selenium rectifier (silicon rectifiers had already replaced that but the old part was left in place as handy connection lugs).
I did run into a few problems after first try - I had left one wire off of the blend switch and corrected that, restoring audio on the right channel. On phonograph function the left channel was intermittent and touching anything on the PC-6 board would cause the audio to come and go. It turned out that one very fine strand of shield wire had gone into the hole in the PC board where the signal lead was soldered. I removed the strand from the hole and all was well.
I listened several hours and found that overall the sound is quite pleasing but just a little more forward in the midrange than my PAS-3X. The tubes I installed consisted of a 1960s vintage Telefunken and a late 70s RCA from my used tube stock. These two tested with the best emission of the ones I had on hand.
I also added a 1/2 amp fuse in a clip-in holder under the chassis. The unit will need a new face plate to look its best. Additional cleaning is still needed and the volume control shaft will be shortened about 1/2 inch to allow the knob to be closer to the front panel.
You can see some pictures at: http://s1213.photobucket.com/user/rubal1...sort=6&o=0
Joe
I did run into a few problems after first try - I had left one wire off of the blend switch and corrected that, restoring audio on the right channel. On phonograph function the left channel was intermittent and touching anything on the PC-6 board would cause the audio to come and go. It turned out that one very fine strand of shield wire had gone into the hole in the PC board where the signal lead was soldered. I removed the strand from the hole and all was well.
I listened several hours and found that overall the sound is quite pleasing but just a little more forward in the midrange than my PAS-3X. The tubes I installed consisted of a 1960s vintage Telefunken and a late 70s RCA from my used tube stock. These two tested with the best emission of the ones I had on hand.
I also added a 1/2 amp fuse in a clip-in holder under the chassis. The unit will need a new face plate to look its best. Additional cleaning is still needed and the volume control shaft will be shortened about 1/2 inch to allow the knob to be closer to the front panel.
You can see some pictures at: http://s1213.photobucket.com/user/rubal1...sort=6&o=0
Joe
