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Dynaco-Doctor Forum Welcome! Need support, you got it. Or share your ideas and experiences. |
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Dynaco-Doctor Forum Welcome! Need support, you got it. Or share your ideas and experiences. |
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In Reply to: Dynaco newbie - Stereo 400 options posted by Maxmano356 on May 10, 2013 at 11:45:27:
If I understand you correctly, you have the speaker outputs from the ST400 going back to the input of the speaker selector switch on the PAT5, and then from the speaker outputs on the PAT5 to your speakers? You say when you "select no speakers on the preamp" the ST400's meters peg. That is really odd - using the preamp to disconnect the speakers should not make any difference in the movement of the meters. Something is amiss there.
So you should carefully go over how you have the outputs of the amp wired to your speakers one more time. Try going directly from the ST400 to your speakers, start with the volume control down, and gradually increase the level. Maybe the problem was how you had the speakers connected through the preamp. (Or maybe somehow the preamp is *seriously* miswired to inject signal into its output if the speaker switch is off. Look at the web site below for schematics and compare those to what you have - maybe you'll find a wiring error.)
Also, the fact that you heard what sounded like a relay thunk once but not after that suggests the output relay may be old and stuck or gunked up. I have cleaned relays before by removing the plastic case, pressing the relay contacts closed manually, and gently pulling through a thin strip of regular old printer paper soaked in rubbing alcohol to remove any accumulated crud. (The paper acts as a gentle abrasive and the alcohol dissolves gunk without damaging anything.) A gunked up relay could explain the lack of output signal from the amp.
That Dyna gear was good (not great) in its time. The preamp (especially the early non-bifet ones with LM301 op amps) was not particularly detailed or open sounding, and the tuner had an issue with rolled-off low frequencies. I believe the power amp was a Jim Bongiorno design (may he rest in peace), and was probably the best piece of the three. (I had a PAT5, FM5 and ST150 (which was derived from the ST400) when I was in college, and I have fond memories of them, but looking at them now, they are 40 year old designs that were built to a price point even back then.)
Are they worth recapping? I would only replace capacitors that have gone bad with age. Because they are cosmetically clean, you'll find a buyer out there somewhere who'll want them for nostalgia's sake. You'll of course get better money if they work, but if you do sell them, leave them as stock as you can - your handiwork will probably reduce their value, not increase it.
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Follow Ups
- RE: Dynaco newbie - Stereo 400 options - JonM 09:36:10 05/14/13 (0)
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