Audio Research PH7

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 

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. 

Thanks Tablejockey. I agree about the tubes. I figured I would at least try and reseat them just to see what if any impact it would have. Further investigation I have determined that it has something to do with Temp as well. When I let the tubes cool and reseated them the unit performed as expected until it got to full operating temperature. Once hot the problem returned. It plays fine until I either mute it or put it in mono.Other than that it sounds great. As long as I don't mute it lol.  The PH7 originally was made with 3 power supply tubes which ARC came out with a upgrade to the unit to convert it to 1 power supply tube. This unit does not have that upgrade and I was considering sending it in anyway to have that done. I thought I would take my time doing that since I just got it and enjoy it for a month or two but I think I am going to just send it in with this new development. The buttons on the front panel connect to a small circuit board in the front of the unit that is not part of the main board so maybe its just simply replacing that board. 

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. 

@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. 

  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.

@gerardff 

i agree that ARC should have found the problem with the unit when In for the upgrade based on the checklist that they say the do whenever the unit comes in for service. However I can see them missing it if it was not exhibiting the symptoms at the time. I would think if it's not a weak solder joint but rather a weak resistor or other component sometimes those things are hard to see with a visual inspection.they say the check for cold/weak joints.  I am however happy you found a work around that you are ok with. 

In regards to the power supply tube upgrade I did finally get a call back from ARC a few days after the unit had been taken to the local tech and the upgrade is still available for $300 and I do plan to send it in, but I am going to enjoy it for a few weeks first. I was told it would be a 3-4 week turn around and with round trip shipping add another 2 weeks  plus another $100 lol. 

I hear you on rolling the output tubes and i have have made a note of the ones your using and I have planned to do just that at some point. The unit sounds so darn good As it is and it is hard to imagine it sounding any better but that is the beauty of the hobby right. 

Regarding it soundibg better with the the top off I wondered about that and may operate it in that way as well. It kinda makes sense when you think about it and I'm sure that is the reason why most of their newer gear has the tubes exposed on the cabinet design. 

Thanks for the info. Good stuff.