As far as output transformer impedence, I am still trying to figure out how that is figured into the equation?
The impedance of the primary is the load the tube works into. Less impedance in the primary, the more current is allowed to flow. More impedance in the primary, less current is allowed to flow. So the impedance of the primary has a direct effect on how much current the power supply needs to provide.
The easiest way to make some decisions here is to just pick your output transformers. The rest of the circuit can be tailored around them.
I forgot to mention, I want to try to keep the PS in tube format. Trying to keep this thing all tube as possible
Well I would recommend silicon rectification since this is a lot of current needed. But...if you really wanted to go with tube rectification, you will need dual 5AR4 rectifiers to support a 50+50 watt amp. The 5AR4 will drop about 35 to 40 volts DC just to run them. So you need to add 35 to 40V DC into the calculations so that when it is dropped across the rectifiers you are left with the plate voltage you want.
If you go with the example I provided in post #7, the power transformer needed was a 315-0-315 secondary. But you need 40V DC additional so that when the 40V is dropped across the rectifier, you are left with 400V DC delivered to the plates. The voltage conversion factor (after transformer losses) is approximately 1.3. Doing some math: 40V DC / 1.3 = 31V AC extra needed from the high voltage secondary winding. Thus, with 5AR4 rectification, you need a 315 VAC + 31 VAC = 346 VAC secondary. That's close enough to 350 VAC, which is a quite common secondary, so you would go with a 350-0-350V secondary.
Double checking the math: 350 VAC * 1.3 = 455V DC (with cap input filtering in the powers supply). Subtract 40V for the rectifier drop = 415V DC. Subtract 15V (an educated guess) to do some additional filtering through a choke) = 400V DC.
Dual 5AR4 rectifiers will require 5 VAC at 3,8A filament current.
4x EL34 tubes will require 6.3V at 6A filament current.
Frontend tubes will require about 2A additional filament current. So you need a 6.3V secondary at 8A. You probably won't find one that big in an off-the-shelf unit, but you could go with dual 6.3V secondaries at 4A each
Summing up for this example, you need a power transformer with the following specs (assuming stereo chassis build):
- 350-0-350 center tapped at 350 mA
- 5V at 3.8A
- 2x 6.3V at 4A
Edcor has a transformer that almost meets specs, the XPWR173. Its specs are:
- 350-0-350 at 400 mA
- 6.3V at 7A
You would need an extra 5V transformer at 3.8A and an extra 6.3V transformer at 2A to round out your transformer needs.
But this is just an example. You really need to know the primary impedance on the output transformers before you get too much further along here.