Mastersound Compact 845 with Pvsane 845T

HI All,
This gets a bit more complicated,I recieved a e mail from mastersound which advised the only way they could advise on the value of the resistor as a mod for the 845t was if they physically had the valve so a engineer could do the required checks.
I dont see that to be rocket science and would have thought they would or could do this quite easily.Even then they stated that it could not be a definite solution in regard to determining the exact value of the resistor.
One would have thought it would be in their customers interests to go down this path and advise customers bearing in mind the PVsane 845T is a god valve and likely wanted to be used by mastersound 845 Amp owners .
If that was not enough I got home last night and was watching TV when the PH5 Pre Amplifier switched on by itself.I thought I had ghosts.checked the on off switch this was okay reconnected the power with the switch removed it still came on.There was a small LED flashing on a circuit board on the same side of the switch.
Both amps are going back to mastersound for repair.It never rains but it pours.Anybody know of a Valve P0wer Amp which would be as good as the Compact 845 which is integrated.going to keep the PH5 when fixed

HI Brf
Sorry for not anwsering your questions .The 845 compact is shiped with standardc 845 Shuagang valves.The shuagang 845B is somewhat different to the 845T hence the need for the mod.Albeit the 845B is compatible with the compact 845 without any modifications.
Re operating specs you are quite correct but I find it very difficult to get detailed information from them.I think this is caused to a considerable extent by the language barrier.They should suply it withe the operators manual which is also scant in this regard.

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

Cobra /Phil
Thanks for that,am I right in understanding that the 845 t would be ok as drop in and have no adverse effect on the existing resistors.Plus, that the 845B is better than the 845T. The amps are going back tomorrow for repair can you suggest any upgrade that would be worth doing such as capacitors etc which would be worth while.Might as well have it done while they are in the hands of a competent tech from Jordan Acoustics in scotland.
Thanks Guys

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