I know my tubes (VT100 mkII) are going when...

Jea48, thank you for the detailed response!

If I decide to keep the ARC supplied input and driver tubes, should I even mess with the bias on those, or should I just install new power tubes, adjust power tube bias, and call it a day?  Obviously that would be easier, but I fear I may be leaving a stone unturned.  The bias on the power tubes was perfect by the way, and I have not checked or touched them since ARC retubed in early 2015.

what do you think of using KT120 tubes in the VT100 mk II? The threads I saw were positive. It seems there is a minor risk of the heaters drawing more power, but I suspect that there is enough headroom in the power supply to handle it.

part of me wants to retube everything, including my preamp. I am devising a plan to build an external tube hour counter, so it would be great to start from scratch with everything, though I also do not want to just throw money away...

i have a dedicated 20 amp breaker with heavy gauge romex power cable in the wall to a single duplex outlet. I use a Shunyata Talos conditioner, and all of my gear is plugged into the Talos, including the power amp.  Do you feel this is ok? Or do you recommend plugging the VT100 directly into the wall?

Thanks,
Mark

Mark,

I would plug the VT100 amp directly into the wall outlet, jmo.....

I do not have any experience or knowledge with regards to the use of KT120 power tubes in the VT100 MK2.
You might want to contact ARC service at the factory in Minnesota.

I found a copy of the schematic wiring diagram for the VT100 MK2.
http://www.arcdb.ws/VT100/VT100.html
Scroll down the page until you come to the two schematics shown.
The first one, on the left, is for one channel of the VT100. The second drawing is for the power supplies. Note the right hand drawing says for the VT100MK2.

I noticed you posted another thread where you say the tubes have more hours on them than you previously thought. You may want to do a complete retube now.
(Unless you have a tube tester and can test the 6922 tubes doing a life test. If you can test the 6922 tubes they must go back in the same tube socket they were removed from.)

Biasing the input and driver 6922 tubes is not for the novice. Lethal DC voltage of around 450VDC will be present where you will be working. You will need 2 meters. Make sure you have clip on test connectors for the meter probes. Side panels on each side of the amp will need to be removed for access to the tube socket contact points where you will attach the meters probes. This is also where the trim pots are located that you will be adjusting.
I suggest you go through Abe Collins’ how to retube the VT100 MK2 a few times before you actually try it yourself, live power.

I can not over state the importance of buying really tight matched 6922 tubes for the VT100 amp.

Jim

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Jim, that is excellent advice.  I agree on the full re-tube.  I am planing to retube my power amp and preamp completely, and at the same time, I am planning to design and assemble a tube hour counting device (described here)

Let me ask a few questions:

1.  I found and used collins's tutorial on biasing the power tubes.  I was intimidated by the signal tubes.  However, I am inspired to learn.  If I want to practice the connections with the two multimeters and agitator clips in a dry run with no power in the amp, how do I ensure that there is no energy in the amplifier?  Should I have music playing and then turn off the power amp so it is still supplying output to the speakers until it fades out?  Or just unplug it and wait a certain amount of time?

2. I spoke to Upscale Audio and Tube Depot on tube matching.  They told me that they match them as best as they know how, and that they do not have a way of offering even tighter matching.  They seemed confidant that their matching is really accurate.  I am leaning towards Upscale Audio, the way that they describe their method and practices seems really perfect.  Do you agree? Are their matched tubes tight enough for the power amp?

3.  Do I need to adjust bias in the LS25 as well?

thanks!

I was intimidated by the signal tubes.  However, I am inspired to learn. 

Part of learning is the knowledge gained from making mistakes.  It would be great if you could watch someone else bias your 6922 tubes the first time. 

Jetter,

I agree!  Any tube veterans want to visit me in Miami for a biasing session?  I will provide a gourmet meal, fine wine, single malt scotch, and a great listening session on the newly biased tubes!

:-) Mark

PS: This is a serious offer