Back to back transformers in power amp

[juancra]

Hi all!

My name is sebastian and i'm really new to this forum. I have no previous experience with tubes, so I wanna build myself a tube amp. In the beginning of the journy I had chosen a design based on cheap radio tubes that I'd found in www.diyguitarist.com (its called Radio Head, its under Guitar FX stuff) to serve as preamp. I started building it and realized that perhaps it would be cool if I build various preamps in different cabinets and use them with a common tube power amp. So I looked up in AX84 site and found some low wattage (cool for my sound needs) tube poweramps.
The problem is that my budget is kind of tight, so I haven't got a lot of money to spend on the proyect. I know that I'll have to spend some bucks in the output transfomer, but I came to think that I could save some money if instead of using a big power transformer I use common transformers 220v / 6 v in back-to-back fashion as used in many DIY tube preamps, so the question I want to make is ¿Can I feed a 6SN7 or 6L6 tube like the ones portrayed here with a power supply based on back to back transformers?

[black_labb]

not quite sure what you mean by back to back. is that refering to using different transformers for the filament to the rest of the supply? if so that would work fine, just make sure you dont have less than 6v (i'd aim for 6.2 min) on the heaters.

[6267]

I think he's referring to taking say a 120v filament transformer, and wiring it's secondary to the similar secondary of a 240v transformer. That would provide both filament & B+, but I think both transformers would need to be somewhat oversized to provide enough current. It would work though, I've seen that done. Personally, I'd find a big old 1950s tube something and snag that transformer. Do you have a scrap yard, junkshop or craigslist? Sure saves some money, but it can get interesting...you really learn to identify useful stuff after getting a carload of something useless. Free tubes, transformers and chassis, sometimes. At least it's cheap, just don't reuse the filter caps or resistors, in my experience they are not to be trusted .

[juancra]

Hello again!

What Im referring with "back to back" is putting transformers in the same way that appears in this schematic



I think that it could save me a buck if I use that configuration instead of buying a big power transformer. The psu feeds both the B+ and heathers through a regulated DC supply. The schematic shown is for a 12AX7 preamp. What do you think, is it possible to feed a power amp with a psu like this?

[6267]

Those probably won't provide nearly enough current. Personally I'd just scrounge something, but if that's not an option use the BIGGEST 12v transformers you can get cheap. It will be drawing amps off the 12v secondary to make the B+. Also, you'll want at least 250v for any power amp, 300-400v is better. That's why I suggested using a 240-to-12v transformer for the second one in your diagram.