04-11-2014, 09:22 AM
I have a ST-70, PAS-2, and FM-1 (with multiplexer) that my Dad built in 1961 and '62. I have been through the ST-70 and the preamp and have replaced all of the black tubular caps, the electrolytics, a couple of out of spec micas, and a few resistors> I matched component pairs where noted on the schematic or parts list. I replaced the electrolytics in the tuner, but not the other caps because they are all ceramic.
One of the EL-34s was missing, so I replaced them with a matched quad of Russian Mullards. After a while I replaced the 7199s with 6GHAs with the adapter. The whole system sounds great, given the mediocre quality of my speakers. The sensitivity of the FM is really impressive.
I've had intermittent problems with balance between the two stereo channels. Replacing the 12AX7s in the PAS-2 preamp with a matched quad seemed to work, but now, only a few days later, the ST-70 developed a balance problem! It's giving me fits. I'll probably start a thread on it once I've had a chance to dig into it and check a few obvious things.
And if that weren't enough frustration, the FM-1 suddenly developed a loud hum that is independent of the volume control. If I turn the tuner volume all the way up and the preamp volume way down, the hum is gone, but it is quite horrible with the volume controls set any other way. Another thread to be started later, I suppose.
One of the EL-34s was missing, so I replaced them with a matched quad of Russian Mullards. After a while I replaced the 7199s with 6GHAs with the adapter. The whole system sounds great, given the mediocre quality of my speakers. The sensitivity of the FM is really impressive.
I've had intermittent problems with balance between the two stereo channels. Replacing the 12AX7s in the PAS-2 preamp with a matched quad seemed to work, but now, only a few days later, the ST-70 developed a balance problem! It's giving me fits. I'll probably start a thread on it once I've had a chance to dig into it and check a few obvious things.
And if that weren't enough frustration, the FM-1 suddenly developed a loud hum that is independent of the volume control. If I turn the tuner volume all the way up and the preamp volume way down, the hum is gone, but it is quite horrible with the volume controls set any other way. Another thread to be started later, I suppose.
John Honeycutt
