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I need the correct way to bias new tubes in my ARC VT100MK111 AMP

First off I am not new to extreme high voltage as I have spent years around it and possess the necessary tools etc. This amp of mine has always and still play wonderfully. My thoughts are that after over twenty years it likely needs new output and driver tubes. So on that note here we go. From all that I have read one article states that I MUST have a CD player connected to the preamp inputs and on with nothing playing. Another article states that I MUST have my preamp connected to the preamp inputs and on but muted. Another article states that I MUST have my loud speakers connected to the outputs. Another article states that ALL ARC amps are designed so that they can be biased without anything connected to either the inputs or outputs of the amp. Now I fully understand the warm up procedure and the actual biasing procedure as to me it is very simple. My plan it to pay a bit more and buy the replacement tubes directly from ARC. So, can one of you guys / gals who without question knows the real answers please tell me what is the proper procedure? Thank you.

warren100
faustuss's avatar
faustuss
818 posts
 

@warren100 

Based on the link to ARC instructions @ghdprentice provided for you I would check the bias first after sufficient warm up and if all the tubes fall between 20mV and 65mV you’re golden and I would put off the search for replacement tubes going forward. It doesn’t matter how old they are but weather they fall within the specified bias parameters. Any vendor will try to sell you new tubes otherwise they’d be out of business.

Oh, as the instructions state consult the owner's manual for complete instructions as it appears the test points aren't easily located and there are further procedural considerations to be observed! You may be able to source the correct user manual online if you don't the original on hand.

rsmith73
47 posts
 

+1@ghdprentice

I owned a VT100MKIII and it is easy to bias.  Before I sold mine, I replaced the output tubes with Gold Lion KT88 tubes.  The best the amp ever sounded IMHO.

I purchased from Upscale Audio and the tubes were top of the line.

warren100 OP
5 posts
 

Once again, THANK YOU to all of you who have taken your time to respond to my questions. Have a great day.

testpilot
1,019 posts
 

When replacing power tubes, be sure to turn down the bias when inserting the new tubes to prevent the possibility of red platting.  Once inserted and warmed up (at the lower bias level), only then can you increase the bias to the manufacturer’s specifications 

warren100 OP
5 posts
 

Thank you for the advice.

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