Sovtek Mig 50 power transformer change

[Ansel]

i'm interested in changing the power transformer in the MIG 50 with VOX AC30  type power transformer for lower voltage on B+, any other suggestion?

MIG 50 :
The plate sits at around +535V and the screen at +530V. The bias voltage is about –58V and the input impedance for the OT is 4.75K Ohms

the AC30 type power transformer gives a  290vac secondary , and with the MIG 50 bridge rectifier it will give about 290/0.71= 408vdc which is very fair on the B+ and ofcourse it will be less on the screen

my question , if i do this change , do i need to change any resistor or capacitor value? or just tweaking the bias knob for the grid?

[PRR]

Welcome.

Just changing the main B+ down about 24%, no radical change needed. G1 bias should be approximately 408/535 of present 58V, around 44V. That straight-line interpolation is a little off, but all tubes vary, so you will dial-in from there while observing cathode currents and plate dissipation.

[sluckey]

the AC30 type power transformer gives a  290vac secondary

Some AC30s use a PT meant for a FWB, others use a PT meant for a conventional FW rectifier. Be careful to pick the correct PT to use with your Mig FWB, or you may end up with twice as much B+ as you want! Also, you'll probably need to modify the bias circuit since the AC30 PTs don't have a bias winding. Fairly simple but it is a big deal.

[purpletele]

I didn't know that we have the polling option,


My poll would be something like, I have re-wired and changed every component:

a. Do you think that little voltage issue took out my OT

b. Should I stick to just playing guita