Transformer Selection Question

[Kaaskop]

Hi EL34 world
I’m new to the forum and this is my first post. I’ve been learning about tube amps and loving it. I have so far made 2 more or less successful builds. A Spitfire and a variation on a Champ. My next project will be a 6V6 JCM 800 20 Watt Marshall (Rob Robinette). However now I see so many great projects generously share by Doug Hoffman that are very attractive, but I guess it will have to be one at a time.
https://robrobinette.com/images/Guitar/Marshall/RR2104_Master_Volume_Micro/RR2104_Master_Volume_6V6_Schematic.pdf
My question is about Transformers. I will use Hammond’s because in Canada they are available and well-priced. Availability, cost and shipping are a problem with Heyboer etc...


Power Transformer
I need Secondary between 290-0-290 to 330-0-330 (150 ma) / 50 Bias / 6.3 volts / 5.V
I give this range for the secondary HT because the site makes references to them all at different points. I’m looking for a good amount of breakup (distortion) but I’d like to keep the 6V6 plate voltage close to 300VDC. My question is will this work with 290-0-290 or is the higher HT a factor in getting the breakup.

Hammond Options
291CX secondary 325-0-325/207 ma - 50 bias – 6.3/4A – 5V/3A
https://www.hammfg.com/files/parts/pdf/291CX.pdf
272FX secondary 300-0-300 / 150 ma – 6.3/3A – 5V/5A (no 50 bias)
https://www.hammfg.com/files/parts/pdf/272FX.pdf
290PAZ secondary 290-0-290 / 140 ma – 6.3/3A – 5V/2A (no 50 bias) amps too low?
https://www.hammfg.com/files/parts/pdf/290PAZ.pdf
270FX secondary 275-0-275 / 150 ma – 6.3/5A – 5V/3A (no 50 bias)
https://www.hammfg.com/files/parts/pdf/270FX.pdf

My understanding is I can create a 50 V tap off the HT line

I haven’t decided on a rectifier yet but keeping in mind voltage drop,
Solid State 4 volts
5AR4/GZ34  10 V


Output Transformer
I need  20 watt / 8 ohms Sec
My understanding is that I need about 6600 Pri ohms for 6V6’s at 20 watts.
https://www.hammfg.com/files/parts/pdf/1750H.pdf
However, on my last build with EL84’s I used 6200 Pri ohms for 15 watts
https://www.hammfg.com/files/parts/pdf/1750Y.pdf
The 6200 Pri is a much more substantial OT then the 6600 Pri option at 20 watts.
I understand the different Pri ohms to watts is because the tubes have different requirements. What I want to know is can I use the 6200 Primary with 6V6’s at 20 watts. My guess is yes but I’d rather not guess.

I’m new to this so all the above information is just my understanding right or wrong and I’m happy to be corrected. I’d graciously appreciate any feedback.