Hotbox power supply trafos

[Aharon]

I once built a Hotbox and I remember really liking the sound a lot.
No longer have it and I want to build another using mostly parts in my toolbox.

The question is ,if I use the transformer back to back "trick".....can I use a 110V-12v-12v as the primary
and a 12V-220V as the second transformer for HV?

The first has 2x12V windings so I'll use one for heaters in series I guess,maybe DC?
Thanks
Aharon

[bancika]

you can parallel secondaries for more current and hook up tubes to use 12.6V (only pins 4 and 5)

[Aharon]

Thanks bancika.
By the way I'm having great fun with diylayoutcreator.
Aharon

[DrNomis]

Because both of the transformers that you want to use have 12V AC secondaries, you should be fine using them, just make sure the 12V AC secondaries have an adequate current output capability to run the Tube/Valve heaters as well as drive the transformer you want to use to generate the +HT, otherwise you might find that the voltages you get a bit lower than expected, for the two 12AX7 Tubes/Valves you'll need 12.6V/ 300mA at least to run the heaters....

[Aharon]

Thanks DrNomis.
I made a guesstimate based on the size of the 110V/12V trafo ,should be close to 1A.
The 12V/220V I know for sure is 1A.
Aharon

[bancika]

At first I made power supply for hotbox like that and it worked fine until I accidentally fried it so I ordered a custom toroid. But back-to-back is ok.
You won't really get 220V on the other side though. 220:12V will do around 14V without load which gives ratio of ~15.7. Multiply that with 12V you'll have from the first transformer and you get around 190VAC without load. Under load you can expect it to fall down to 170-180VAC. When rectified you'll get around 240-250V which is perfect for that kind of preamp (you can go up to 400V)

[Aharon]

Thanks again.
Aharon