Aleph 2

Volkerk

Member
2001-12-25 10:03 am
Hello,

I built the Aleph 2.
Whitch transformer should I use. I need +-45V d.c. also I need 32,14V a.c. But I dont't can find a transformer with 32 V. Can I use a transformer wit 2x36V a.c? Is a 600VA transformator ok?

Whitch restistors and witch dide should I use?

thanks

Volker
 
www.plitron.com has a nice selection of transformers rated at 625VA. Either the 097019201 (33-0-33V) or 097018201 (35-0-35V) would be good choices. Avel-Lindburg probably has transformers in that same range as well, but I don't have a list of their transformers handy.
Higher VA is nice, but costs more, of course. I believe the production unit used a 600VA, though, so anywhere in that area will be fine.

Grey
 
Hi,

I'm interested, in building the aleph 4,
I already have two transformers wich I have set parallel on each other (it works), because they have the same voltage (2x35V AC) one is 300VA and the other is 450 VA wich makes 750VA.
Should this be enough?
Or should I buy a bigger one?

Thank you.
R. Blankesteijn
 
Grey,

I disagree, paralleling two transformers of the same voltage, but different VA ratings will work fine. As the load increases, the smaller transformer's output voltage will decrease quicker than the larger one, reducing the current draw from that transformer, and balancing the power. In the real world things aren't that nice, and the balance won't be properly split between the two transformers, but you will get a usefull increase in power.

There are a few other factors to consider. You will have to use seperate rectifier bridges, and combine the supply rails after that. If you join the transformers at their secondary AC out, then at no load, a potentially large current will flow. Imagine a 0.5v difference between the two transformers, and the secondary windings are 0.1ohms. A current of 5A will flow, which may be a problem.

Cheers, Adrian
 
Adrian,
You start out disagreeing with me (no problem there), but sound as though you're agreeing with me by the end of your post (no problem there, either). I might try such a stunt myself, if it were late on a Saturday night, and I was desperate to try something before going to bed, but...neither of us will be there to watch R. Blankesteijn's circuit come up. If the experiment goes badly, things could get ugly. I prefer to play it safe in cases like this.
Micke,
My thinking is that the smaller transformer could overheat, due to being asked to deliver too much current. There are many variables here that are beyond our knowledge, such as the impedance of the secondaries of the two transformers in question, how conservatively the transformers are rated, etc.
As a general rule (barring late Saturday night experiments) I prefer to parallel (or series, for the matter, although there are neat tricks you can play with series transformers if you watch the current draw) identical transformers.

Grey