Easier maintenance ARCVT100mkII or VTL mb125

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.

Hi Alun,
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.
Good Luck,
Steve

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.