Audio Research LS25 MKII Problem

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Good news

Okay, well I think I found out the problem! Our house is old and has shoddy electrics, I did my best to fix some of it when we moved in. The outlet the pre-amp was plugged into has an intermittent earth problem. I now have it plugged into a different line, and was just running for 3 hours with no problems. Thanks to everyone is offered some help.

You may want to return the tubes and have thetubestore test and certify. If they come back good, think about returning the LS25 to seller and let them get it fixed.

Sorry to hear and I hope you get resolved soon, and post back the problem and fix! I added the same amp a few months back and it has been great with no issues.

I'm in San Antonio TX. There is a guitar place in town that sells tubes, maybe he can test them. They are 6H30s though so I think I read they don't test on your average tester. I could just buy another set of tubes and keep as spare. There is a couple of technicians in town who I could ask about looking at the unit, one is more vintage radio/cb radio I think he was Vietnam era military radio engineer, I'll start with him. If anyone knows a good technician in San Antonio or Austin area?

Thanks

Where are you located? There may be a technician close to you that can check the tubes. The alternative is to send the unit to Audio Research for a checkup (think $600 and up).

It came with out tubes but that did cross my mind, but they sound perfectly fine. I got from thetubestore. Don’t they test all their tubes. I even paid for matched. Seems unlikely they send faulty tubes?

Put the old tubes back in and retry.

I’ve owned ARC preamps for decades and never had an issue with the muting circuit itself. The most likely explanation for your issue is that the muting circuit is doing its job and you have a bad tube.

I just googled "audio research muting" and I see as you say other models affected, sp1 sp6 and sp10 so far. I'll keep reading and see if anyone finds a solution. It seems to of settled down now. Hopefully its just occasionally and not every day thing. Thanks

That was a common problem of the muting activating going back to the SP6. I don't know if ARC came up with a fix for this? A shame if their later preamps suffer from this!