Do not know about the VTL MB125, however, the ARC VT100MKII can be tricky and expensive to re-tube. Try
http://mycollins.net/audio/ He goes through the re-tubing procedure for the ARC. (Nice detailed pictures) Last time I checked with ARC, the cost to retube the 100MKII was in the $800-$1000 range plus freight.
I can't comment on the ARC or VTL. But, you can get autobias tube amps. Wolcott's and BAT are 2 examples...
Ease of maintenance led me to the BAT VK-60 with autobiasing. No need to mess with meters and small tools.
The expense and hassle of ARC Tube amps caused me to switch some time ago. Except for the latest model, biasing them was a PITA (for me anyway). There are a lot of amps which allow bias of each tube individually using either an LED or a meter (built in or otherwise). These are easy to use and for the most part allow you to replace individual tubes with like kind and quality with out the need for matching. Auto bias is convenient but not necessary.
Customer usually has to adjust bias because playing around NOS tubes(especially those unproved sources). Standard 6550 on ARC usually don't create problem, I used to own ARC VT100II and classic 120 for total of 6 years(no problems). I am not sure how much freedom you can try differnt tubes on auto-adjusted ones. Also, another Agoner posted before thought his BAT-60 has shorter service life time than his ARC classic 150. I never need services for bias on ARC's amp while owning them(maybe my ears are not golden ones). Once dial-in with reliable tube sources, they are stable. If you play around with differnt tubes, I guess you must be a tweak guys and should not be bothered to rebias them. Some friends have to constantly adjust his tube amps(not to mention the brand), and that's pain!
The ARC has a resister that you clip on aligator clips to to connect to the multimeter and the vtl has two holes that the probes go into. Remember the tubes are hot and your working very close to them so your concentration is required. It takes about 1 minute or so per tube to do each one and after your done with the last tube go back and double check them all again. If your new at this just call the company. Leonard at ARC spend 20 minutes with me on the phone the first time and walked me through it . I was hooked on ARC after that level of service its tough to beat. The ARC VT-100 is a magical amp closer to a work of art than an audio component. Tubes simply sound better more musical and "Just Right" like CJ says. They are worth the extra effort. You only have to bias twice a year or so.
I think IG40 comment to check "mycollins.net" site is a great idea, very interesting and has correct proceedures.
Bias the power tubes in the VT-100 is straitforward, adjusting the input/driver tubes is a little more interesting and will require some basic electronic's backround. I would not try this proceedure without two volt meters.
It is my understanding, ARC recommends adjusting the driver/input tubes at the same time you make a power tube change with the VT-100 original and Mark 2 units.
If you were to purchase a second hand VT-100 amp, several ARC dealers and other service centers can correctly complete this tube replacement/bias service without sending the unit back to ARC. Maintenance should not be to difficult but may require a local Tech for assistance.
That is incorrect. There is no requirement or reason to rebias the input tubes when you replace output tubes. The bias control on the output tubes has no effect on the input & driver tubes. ARC recommends replacing the input & driver tubes after two replacements of output tubes. In reality, the input & driver tubes can go longer than two sets of output tubes, probably three sets before their life is beginning to wane.
I own the VTL MB-185's. Biasing of the output tubes is accomplished via individual trimpots accessible through the top panel once the tube cage is removed, and adjusted using a narrow flathead screwdriver. Each trimpot is associated with its own meter probe receptacle, the other probe being attached to the 'negative' speaker terminal. The only difficulties, if you want to call them that, are that you must own or purchase an appropriate multimeter (selection guidance is given in the manual), and the trimpots themselves tend to be quite touchy, responding somewhat imprecisely to very small turns. I've used easier (Conrad-Johnson), but there should be no problem doing this operation yourself. As far as retubing goes, VTL runs the tubes conservatively and they should last a long time as a consequence. Tube types are not exotic, rare, or overly expensive, though as usual, expect to pay a premium if you choose to retube through the manufacturer instead of buying from a tube retailing specialist.
What fantastic responses from all!!! I thank you for your input and advice. It seems a lot of people own the ARC amps and have mixed reviews regarding their upkeep. Although I've contacted a couple of people with the VTL's they seem a little more staight forward and user friendly. I will check out the "Collins" website that everyone suggested and make sure. Unfortunatly there are no AR/VTL/Rogue dealerships in the local so I cannot hear them to make personal judgements. Therefore I must rely on fellow Audiogoner's for their input. Thanks a bunch
All of the above notwithstanding, I'm pretty sure the biggest deciding difference between your contenders will be sound, not maintainance. Search the Audiogon archives for more - related questions have been asked before.
That is true Zaikesman, but I don't want to have to be sending a 100lb amp back to the manuf. every couple of years. Hopefully I will be able to find some balance between the two, sound and servicablility.
Thank you for all of the responses
I have the MB-125's and the biasing procedure is exactly as Zaikesman has described. Straightforward, easy to do, not particularly time consuming, and except for the one time cost of a $20 - $40 meter (mine's from Radio Shack and works like a charm), it's a no brainer. The replacement tubes are reasonable (your favorite brand of El-34's) and once you set the bias there's rarely much drift if any for long periods. - I check mine about once a month or so... and usually find just the slightest of drift now and then which takes a brief moment to "touch up". It's a beautiful thing. By the way, the amps themselves (besides being a DELIGHT to own) are absolutely wonderful. I've already mentioned their ease of use, the reliability has been exemplary (no problems at all in almost 3 years of use) and the sound IS fantastic. 3D like only tubes can really do, dimensionality, finesse and upper extension but with a bass control that not only belies tubes but sounds way more potent than 125 wpc ever had the right to. Throw in the tetrode/triode switch for whatever music delivery suits your mood or listening choices for the particular session.... and the only thing I'll ever consider trading mine in for would be a move to a much bigger room and the need for even more power. The MB 450's are on my long term wish list. Anyway, I'm gushing here and that's not what you were asking about but, nothing against ARC at all, the VTL's really do "make tubes user friendly", and well worth doing. Good luck.
Could someone provide me some hints to rewire my monoblock to accept 110V input instead of 240V? Thanks for your response.