2. amps-preamps
  3. 130817-8622

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

I'll begin by saying that I do realize a lot has been discussed on this subject. I read a lot of threads here.  Here is my situation:

1.  ARC retubed and did some other maintenance on my VT100 mkII in April 2015, so they are 3 years and 3 months old.

2.  I have no Idea how many hours are on my tubes in my power amp or preamp.  Tube timers came in later models. Darn, I want a tube timer! (Side note, anyone know if there is a good external or accessory tube timer to buy?)

3.  I learned to check bias on the power tubes, but have not attempted to measure the signal tubes yet.  I am ready to try. I have the tools (need one more multimeter) and I like to be hands on.  When I checked the power tubes 2 weeks ago, they were perfect, despite not being checked or adjusted since ARC did the service in 3/2015.

4. I could be crazy, but I think my system is not as loud as it once was. I am not sure about a diminished sound quality, but it is possible that has occurred very slightly.  No noisy tubes or bad tube static though.

5.  Loads of people spoke about installing KT120s in this amp. Are people in agreement on this?

6.  Is The Tube Store reliable for well matched tubes?

thank you everyone!
- Mark


marktomaras

Showing 3 responses by marktomaras

marktomaras OP
544 posts
 
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





marktomaras OP
544 posts
 
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
marktomaras OP
544 posts
 
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!
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