Help on 300B power trans...
I actually ran this in Power Supply Design, but thinkin’ it might be better here.
I am getting ready to order two power transformers for my first 300B mono blocks. ElectraPrint has requested the Volts and amps of each secondary winding. DuncanPSUD2 has supplied me with the information I need for the mains, but the question I have is for the current (amps) for the remaining secondaries. Simple questions I know but like I said, this is my first 300B, just want to make sure…
From the attachment:
The heater supply for the GZ37 is requiring 5V and 2.8 amps for the current taken from a fact sheet. Would it be correct to say – 5V/2.8 amp for this secondary?
This amplifier is a mu-stage with a 6AC7 – 6SL7 combo, both tube heaters requires 6.3V, 6AC7 needs .45 amps whereas 6SL7 needs .3 amps, O.K. to choose the higher value for both? It is also center tapped, how about – 6.3V/.45 amps - CT (?)
Last but not least the secondary for the 300B, it starts as a 6.3V and ends up after being rectified at 5V. How would I determine the amps needed here? The 300B calls for 5V/1.2 amps, sooooo - 6.3V/ (?) amps…
Note, I just finished visiting Boozehound’s site and noticed that he gives his heater amp a bit extra, i.e., 5Y3 asked for 2.0 amp and he specified 3.0.
Any help would be great!
On the rectifier filament, I would specify 5V 3A. That's the "standard" and will let you use other rectifiers (like 5U4, 5R4, etc.)
For the 6.3V winding, you need to add the current requirements of the tubes. So you need a minimum of .45 + .3 = .75A. You would be safe specifying a 1A current to give you a little headroom.
For a DC rectified winding, there are many rules of thumb, but you typically multiply the DC current needed by 1.8x, so 1.2A x 1.8 = 2.16A. Sometimes it's best just to tell the transformer designer that you will rectify it and draw 1.2A DC from the winding, and let them size the winding appropriately.
I'd just send the schematic to Jack at electraprint, he will know what to do, I think...
Its a good chunk of change to put down for these transformers and your conferring reccomendations - puts it at rest.
Best - Stan
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