Suitable power transformer for 6L6 Champ build

[Resonator Guy]

One of my winter projects this year will be a Champ build in a neat cabinet I have. How do I go about figuring what PT to use with a 6L6. I know it isn't much of a change sound-wise, but I want to do one a little different this time and I have some NOS 6L6 tubes to try.
I have been considering a PT from AES with secondaries of 325-0-325 V, 375 VDC @ 70 mA(DC )
What do I need to consider other than mA needs.
This is the cab I will be filling.

[Alan0354]

Take a look at Weber. It is a little beefier all around in spec. https://taweber.powweb.com/store/022772sch.jpg

This is there site:https://taweber.powweb.com/store/magnetic.htm

The current of HV and filament and floating filament spec are the things I am looking for and you'll find the weber transformer always spec a little more than requirement. 6L6 draw a lot more filament current than 6V6.

[Resonator Guy]

Thanks Alan, but what I was asking more is what calculations are required to determine PT suitability.

[Alan0354]

I looked at some OT for Champ in Classic Tone, it is a single end power amp, some have 5K and 7K tap. Being a 6L6, you use the 5K tap. For +B=375V, assume the 6L6 can pull down to 75V. So the peak swing is from 375 to 75= 300V. For 5K primary, the peak current is 300/5000=60mA peak. To run in Class A for SE, you need at least 30mA ( half the peak) to keep the tube on 100% of the time. For class A, average current draw is the same with or without signal. So theoretically you only need PT with 30mA. So 70mA should be enough. 100mA is even better.

The real thing you need to look at is the filament current requirements. 6L6 draw 0.9A of heater current vs 0.45A for 6V6. there is definitely an increase using 6L6. So Weber is better as it spec more filament current.

[Resonator Guy]

Thanks Alan, That gives me some good detail to start working with.

[Alan0354]

If you are building from ground scratch, consider this OT. It's bigger than the original Champ. It's 15W. 40-18031.

I don't know the detail of this transformer. It is critical to choose a single end OT. Single end is not like Push Pull at all. There is imbalance DC current flowing in the OT. This can saturate the OT. Usually the OT has to be designed a little different in hifi with bigger air gap to avoid core saturation. It is not as critical in guitar as the frequency does not dip as low as hifi application. BUT if you change to 6L6, you can run in higher current and get more power. You are stressing the original small OT.

You can also look at other brands OT, I am not endorsing Classic Tone, just the first one I look at. You want to find one that can take a little more power than the stock replacement OT for Champ.