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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
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.
wlutke
696 posts
 
Trivia - There is a (square?) button on the main board to reset the tube hours counter to zero. Two 6H30 power tubes were replaced with one 6L6G/5881 tube because of short life and high failure rate. The 6922 signal tubes can be rolled with outstanding results. I have a used PH7 for 4 years now and very reliable. Great pre! It works best with .5 mv carts although my DV XX2 MKII is .28 mv and works great. The PH7 is very quiet.
barnettk OP
410 posts
 
@wlutke Good to know on reseting the tube hours. I figured there had to be a way to do it since tubes can be replaced. I agree that the PH7 is an outstanding pre. Great sound staging and very quiet even though I have not had the power supply upgrade. I have a call into ARC to see if that upgrade is still available. After more testing this appears to definitely be a temp problem and most likely with a bad resistor or maybe a cap. If I remove the cover to allow more ventilation the problem does not occur. Once I put the cover back on 15 mins later after heat collects in the cabinent the problem is back. Sonically there is no problem. it sounds fantastic, but don't want this to lead to a larger problem down the road. I found a guy here in the Atlanta area that specializes in tube gear and I am going to drop it off today. If I send it to ARC Im sure that i can count on being without it for 4-8 weeks. I will post back to let you know what the problem turned out to be. Thanks for all that replied. 
barnettk OP
410 posts
 
  Hi guys well we found the problem with the PH7. The mute relay was bad. The tech found the problem in about an hour including the time it took to fail. Right under $200 to fix the problem. Hopefully we have had our glitch for this mission.
Thanks for all the help. Back to the music.
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