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In Reply to: RE: ST-70 and PAS posted by petercapo on June 30, 2017 at 16:55:16
Thank you for the input petercapo! I was thinking PAS 3. How did you know it was a PAS 3X?
After the brief research I've done I have to agree with you on a refresh. I plan to replace tubes and do power supply updates and see how she sounds. I like things original if I can.
Follow Ups:
Whoa on replacing the tubes! If it has the original Telefunken 12AX7, they are worth $$. If they are other old stock tubes, they are still valuable, and they have a good chance of still being "good" and sounding great. However, if you are planning on doing work on your PAS, then definitely get an inexpensive current production set of 12AX7 and use those until you are sure your PAS is stable.I know it is a PAS3X because it has the 1.0uF output coupling capacitors (the two small, black capacitors connected between the inside front panel and PC5) and the offset notches on the treble pots. It also has the aluminum faceplate and matching knobs.
The label on the back panel has the later Dynaco logo, so I am not thinking this preamp started out in life as an older PAS-2, which had a somewhat different back panel label. But, later PAS-2X might have had this same kind of label and the owner might have replaced the brass faceplate with the aluminum.
It has four light green coupling capacitors on the PC6 phono board, which I believe Dynaco used in some later production runs, though it still has the brown phenolic PC boards. I estimate this is a late 60s/early 70s PAS-3X. There might be a date stamp on the power transformer or the quad section capacitor. There may be a date code on the backs of the potentiometers, but I don't recall how to interpret them.
If you are thinking of retaining its originality, then I highly recommend, and commend, the Audioregenesis studies of the PAS and Dave Gillespie's study of the Stereo 70. They are landmark works and indispensable:
Edits: 06/30/17 06/30/17 06/30/17 06/30/17 06/30/17 06/30/17 06/30/17 07/01/17 07/01/17 07/01/17
Wish they were original Telefunkens. Tubes were replaced. Like you, i was thinking she was pretty unmolested.
suggestions on a good set of tubes for the PAS and ST-70? Does Mesa Boogie make their own tubes?
As far as I know, Mesa Boogie does not manufacture their own tubes. I suspect they have them made in China to their specification or they just relabel Chinese, JJ or maybe some of the New Sensor tubes.For current production 12ax7, I find the Mullard to be on the warm side while the Tung Sol is more extended and lively. For the phono section, the Sovtek 12AX7LPS is supposed to be a good choice because they are quiet and sound good besides. Buying them from a good tube seller is important, too. For 12AX7 tubes, I like McShane Design and also ebay seller jspht8338. At one time, both were willing to sell me small quantities of matched/balanced 12AX7.
As far as tubes for the Stereo 70, it kind of depends on what configuration your Stereo 70 is in. Is it the original circuit or has a different circuit been installed? Photos?
Edits: 07/06/17 07/07/17
Thank you for the input!
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