How should I connect an old tube transformer

[mdr30]

Haven't worked with an old transformer like this and need some help to connect it, maybe from German readers.
Primary is easy enough, 8 and 5 for 230V (and a jumper between 7 and 6), but secondaries escape me. As an example it says:
11 . 12 . 13 2x240V (Doppelweg gleichrichtg.)

How should 11, 12, and 13 be connected? And what does this mean:
"Anodenmitte (12) an Masse legen"?

Looking forward to be enlightened!

 

[petertub]

Ahh, those old elfa transformers !
the secondary is adjutable, note that the midpoint (12) is used in all combination and that the outer pointe are moved to accomodate different values. All of them are for a middle grounded (12) and the "outsides" uses a single diode.
2x240Volt uses 12 to ground 11 and 13 each with a diode to B+
2x260Volt uses 12 to ground 9 and 15 each wih a diode to B+
etc

 

[jcalvarez]

12 is the secondary center tap (CT). Then you have to select the other two wires for a full wave rectifier depending on your desired DC voltage:
11-13: 480V CT
10-14: 520V CT
9-15: 560V CT.

 

[gijser]

"Anodenmitte (12) an Masse legen"?

"connect the anode midpoint (12) to ground"

When using a rectifier tube with two anodes, these would be connected to for example 11 and 13, and 12 would then be in between the anodes and connected to ground.

 

[mdr30]

OK, now I get the picture. I was hoping to use the transformer in this PSU:

Would it work connecting 11 and 12 to the rectifier?

 

[grovergardner]

No, don't do that. Just substitute a pair of diodes for the bridge and ground 12. But be aware that the secondary is only rated for 85mA. That is probably enough for your circuit.

 

[chrisng]

Since the supply voltage is 230V and the transformer primary winding is 220V, my suggestion is:

If C3 uses a 470uF/400V capacitor, do not use a tube rectifier, and I think C7 should use 10V or higher, not 6,3V.

 

[mdr30]

Thanks. I think anode voltage should be 195V in this circuit, if I understand things correctly. Here's a link to the amp with schematic:

http://www.jogis-roehrenbude.de/Leserbriefe/Siemens-C3g/c3g.htm

Any further thoughts would be appreciated.

 

[petertub]

chising made the best suggestion. Adding to that : replace the B2 with 2 1n4007 diodes. Less complex.

 

[gijser]

Would it work connecting 11 and 12 to the rectifier?

It would work, but then you are only using the part between 11 and 12 of the secondary winding. When you do as chrisng says, you use between 11 and 13, so twice as much. Now the transformer is used more efficiently. But, for a low power headphone amp I guess it doesn't matter much.

 

[mdr30]

Right. I was just thinking of getting the anode voltage right, what it would end up with after filtering and resistors (500 + 500 + 6,8K). But I guess the C3g could take higher voltage than 195V as well.

 

[gijser]

It is hard to predict the voltage exactly, I would just build it, and if it is too high you can increase one or both of the 500 ohm resistors to drop more voltage.
500 is an odd value, probably two 1k resistors parallel to share the heat?

 

[mdr30]

Good idea - will do. Now I've got the transformer, tubes and sockets. Will order the other parts soon. And so to the case, think I will build the whole thing on the top lid so I'm looking for an appropriate box where the top lid is easy to remove. Any suggestions?

 

[Logic800]

Modushop in Italy have a good range. I've used them several times with great success. https://modushop.biz/site/