2. amps-preamps
  3. 1045887478

ARC LS25 MK1 Trouble-Shooting

I would appreciate any comments on trouble-shooting the following problem. I moved my Audio Research LS25 MK1 pre-amp to a new audio rack and re-started my system. Initially everything sounded fine for a few minutes until I heard a "pop" sound from one speaker with the source material (tuner) still being amplified. I changed my source from tuner to CD and there was initially no problem. After about one minute the only sound was a hissing from the one channel and then my power amp shut down. I replaced the pre-amp function with that from a receiver and everything operates correctly. As for some history on the ARC LS25, I purchased it used here on Audiogon about a year ago and have had no problems. I also powered up the ARC pre-amp and verified that all four vacuum tubes were glowing. Is there anything else that I should check before calling Audio Research on Monday? Thanks for your help.
blc1800
bobgates
535 posts
 
Sounds like one of the 6DJ8 tubes in the line stage went bad.
gmorris
351 posts
 
I agree with Bobgates.
You can isolate the tube by swithing the tubes from L to R channel.

george
blc1800 OP
1 posts
 
Thanks for the correct diagnosis. I replaced the existing tubes with a spare set of Sovtek 6922 which I received when purchasing the unit. Some additional questions: when initially turning on the system there was some crackling sound that went away after the first few seconds- is this normal? Also, is there a burn-in period for new tubes and what are the different "musical" attributes of the various tube manufacturers. Thanks again.
j_k
234 posts
 
The only time I have heard crackling sounds from my LS-25MK1 is when the tubes were shot.... It never does it now.. Make sure the new tubes you buy are fairly well matched or you may get a "ringing" sound when changing the gain level... Burn-in on tubes is usually 48 hours for a fairly decent sound. I would also leave the preamp on the lowest gain setting with no input for 2 hours before listening to new tubes... This lets them start up "slow".
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