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Help me find a transformer......

mark norwine

Member
Messages
17,205
I'm designing an effect that will be built into a 1U rack and can't find a PT that will fit. Specs:

- 120V pri
- E-I or Toroid.....I don't care.
- The blank rack box I'm using has a useable internal height of 1.42 inches.....I'm bound by that limitation.
- The effect will have 2...*maybe* 3....12A_7 tubes, so what I need is:

>>>winding #1: 6.3Vac CT @ 1A
>>>winding #2: ~240vac @ 12mA [max] No CT needed; I'll use a bridge.

I've looked all over.....can't find anything that small (electrically & physically).

I know I can use multiple transformers, I know I can front-to-back them, I know I can boost the windings, etc. But I'd really like to find one (1) discrete PT that will drop in & work. "Ear mount" greatly preferred.....but if you know of a suitable PC mount, I can make a board.

Ideas?

Anyone?
Anyone?
Bueler?
Anyone?
 

12AX7

Member
Messages
98
Hammond:

229A230 for 320vdc B+

229A12 parallel for 900mA 6.3v

229B230 and 229B12 for more VA and mA

(build on pcb or eyelet board)
 

mark norwine

Member
Messages
17,205
I spent a lot of time on the hammond website last night, and I think separate transformers may be what I need to do.
 

12AX7

Member
Messages
98
I spent a lot of time on the hammond website last night, and I think separate transformers may be what I need to do.
I like the 229a series because they're less than 1.5" W x 2" L x .875" H, semi-toroidal, and most of all inexpensive! :aok
 

VacuumVoodoo

Member
Messages
1,545
How about getting an OTS standard 120V/12V ca 2A transformer, run heaters off 12V AC, rectify and :idea run a DC/DC converter for the HV ?
You can build a decent one with a photo flash capacitor charger chip like this one from Linear Technology.

Of course it's a little more complicated than a raw transformer and can give you problems with FCC if you're planning on volume production, but for a single unit or two it's cheaper than custom trafos. DC/DC converters are fun.:banana
 

mark norwine

Member
Messages
17,205
I bought two low-profile Hammond's last night from Mouser.....a 230vac & a 6vac.

It's a simple solution that fits; perhaps not as elegant as a single transformer, but for $11 each, who's complaining?

mn
 

terminal

Member
Messages
142
two separate transformers: 1 for the filaments, 12.6v .

and another one, either a 120v or a 240v. you can use a voltage double circuit for the power supply (ala the Atlec 436C) with a 120v and get 250v-270v for the plates.
 

donnyjaguar

Member
Messages
4,194
Like terminal above, I made a tube preamp in a 1u box. I used a 12V transformer that had two windings on the secondary and two on the primary, so that it could be used with 120V or 240V input. I used only the one 120V on the primary, ran the filaments from the secondary paralleled and put a voltage doubler on the unused primary. That gave me about 300Vdc to play with for the two 12AX7 tubes' supplies at just enough current. Its not a big transformer at all but keeps its cool okay.
 




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