Mastersound Compact 845 with Pvsane 845T

Brf, the first responder to the OP, is correct. The 845-T operates to the RCA/Amperex spec, as does the stock 845A tube, and the B. Every Mastersound Compact 845 amp I've ever seen shipped stock with the prosaic Shuguang 845A, a cheap'n'cheerful power tube. 845-T is a drop-in replacement for 845A and 845B, but it is not a clear improvement over 845A, while 845B generally is. If for some reason you don't want to use 845B, consider the cryogenic 845A sold by ATSI.

Precise bias is desired, but these SET amps have enough latitude to allow drop-in replacement for RCA-spec tubes. If you want to address tube-to-tube inconsistency, then sure have a tech install the right resistor. But doing so is prompted by wanting to address inconsistencies rather than an intrinsic incompatibility with the 845-T. My guess is Mastersound's techs in Europe have no experience with the 845-T and are reluctant to endorse a tube substitution they haven't previously tried.

Phil

Patal,

Unless something has been done to your amp to make it incompatible with RCA-spec 845 tubes -- and if it's running 845A, nothing has -- you can replace 845A with 845-T or 845B. It may be that if subsequently you had the bias checked, testing might suggest that a precise adjustment to the value of the associated resistors can dial in the amp more perfectly. Maybe. But you're not going to harm anything by that simple change of tubes.

Whether you will think the 845-T is better sounding than the 845B, or not, is your call. I did not find the 845-T to have clear advantage to warrant using it, and in my own experience with the tube and observation by others who have reported results to me, I have to conclude the 845-T is less reliable than the 845B. Others may have a different experience. Other than the B tube, my suggestions for not-too-exotic alternatives are the Sophia 845MkIII, and the cryo'd 845A sold by ATSI. Interesting exotic alternatives include the KR -- likely requiring some changes to the filament supply -- and the super-scarce Elrod; expensive! Or for that matter, go hunting for a pair of NOS RCA or Amperex. Also dear.

The major area for upgrade that I suggest you have your tech investigate is recapping the power supply. The power supply caps have a strong influence on the voicing of vivid tube amp like this, and on its dynamic character. The Mastersound SET amps sound a little "slow" compared to my Audion equivalents, to me, and I think this can be easily corrected by judicious selection of capacitors to recap the power supply, and you can pick up more transparency in the bargain. Certainly while a tech has the amp for repair it is easy enough for him to precisely bias the amp for the tubes you choose, too.

Phil