2. analog
  3. 129692-78269

Audio Research PH7

Hello everyone. Going to post this in this forum as well as the amp/preamp forum. Just want to run this buy you guys to see what comes out of it. I recently purchased gently used Audio Research PH7 phono preamp. The Preamp had 3 hours on the tubes according to the display. I have had it for a week now and till now it has worked flawlessly. Typically I will mute the preamp to change records, etc. Today I muted changed a record and when I unmated the right channel did not play. turned the unit off and waited for about 10 mins and powered it back up, and the right channel came back. muted/unmuted right channel goes out. According to the seller the PH7 lay dormat for a few years prior to selling it. I am wondering if it could be one of the tubes could simply be failing, but it seems more like a curcuit problem than a tube problem. Any thoughts or experience with this particular issue with the ARC PH7?
barnettk
randy-11
1,913 posts
 
does it have any electrolytic caps in it?

age?
barnettk OP
410 posts
 
Randy-11 I would assume so, but not sure. When I purchased this unit I was a little concerned about if the caps could have discharged while sitting so long, but I would think that would take 15+ years for that to happen. I am not a electrical engineer but based on what I have read it would take longer than a few years. Could be wrong about that. 

barnettk OP
410 posts
 
Randy-11 according to the shipping labels on the box it was shipped from ARC in 08.. it has been used since then but obviously with only 3 hours on the tubes not much since then 
barnettk OP
410 posts
 
Ok just took a look and yes there are several large electrolytic Caps on the main board. A couple on the piggy back board that the front panel buttons connect to. Visually they do not look bad i.e not deformed, or none are leaning or discolored. 
jmcgrogan2's avatar
jmcgrogan2
6,346 posts
 
@tablejockey , +1. I doubt it is the tube, but it won't hurt to try.

Sounds like it could be a cold solder joint, as temperature seems to have some affect, or a capacitor. It could have been a weak cap to start with, however, two enemies for caps are high temperatures, and dormancy. 
Lack of cycling (on/off cycles) and/or high heat can shorten a capacitors lifespan significantly.
More to discover