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trombone 15th May 2006 03:14 AM

Transformer problem
 
Probably a stupid question. I have a transformer that seems to be failing. That is, its voltage output, AC and DC, is lower than normal. I find no cause (which doesn't mean I've thought of everything) other than it's failing. But I always thought transformers either work or they don't. I wasn't aware they could weaken gradually. Or am I way off base here?

Assuming it is, does anyone have an idea where to get another one. It's 10 volts and 10 amps. A high current filament supply transformer.

ray_moth 15th May 2006 07:41 AM

Quote:

That is, its voltage output, AC and DC, is lower than normal.
Not sure what you mean by this - what DC output? Are you rectifying the heater supply? If so, it might help to describe the circuit you're using.

trombone 15th May 2006 09:01 AM

Yes, it's a heater circuit on a tube preamp. The Transformer feeds a voltage regultor. Usually the DC off the rectifier and going to the regulator is around 10 volts. The regulator drops it to 6.1. Now the DC going off to the regulator is about 6.4, which does not supply enough drop voltage.

The AC voltage on the bridge seems low, too. About 10. I think it was higher once.

I'm still trying to see if something is wrong in the circuit that I missed, but I'm running out of possibiities. I haven't found a short, the input cap is okay, etc. but my question was basically about the transformer itself. I had always thought they worked or they didn't. I wasn't aware that they could weaken gradually--if they can.

Craig405 15th May 2006 09:11 AM

Hi,

Transformers dont degrade over time, but they can overheat and possibly short out secondary windings causing the voltage output to change.

If you remove all load from you transformer you should get about 11/12v at a guess, just a bit higher than the rating of 10v. If thias is the case which it probably will be the transformer is fine and you may just be drawing more current than you were before when the voltage was higher.


Regards
Craig

cliffforrest 15th May 2006 09:29 AM

your (bridge? - you don't say!) rectifier may have failed and you are only getting 1/2wave rectification.

Any chance of 'scoping it?

EC8010 15th May 2006 10:30 AM

Quote:

Originally posted by Craig405
Transformers don't degrade over time,
Their cores can degrade - it doesn't lower the output voltage, but the consequent core saturation causes plenty of leakage flux.

Craig405 15th May 2006 11:09 AM

I stand corrected.... learn somthing new every post :)

EC8010 15th May 2006 12:36 PM

I couldn't believe it the first time I saw it causing hum bars (induction directly into the neck of the CRT) but a search coil and replacement of the transformer proved the point. Since then, I check transformers with the search coil...

ray_moth 15th May 2006 12:45 PM

Is it possible the primary of your tranny isn't getting its full voltage: either because the mains voltage is low or because there is too much resistance somewhere in the feed to the primary?

trombone 15th May 2006 01:41 PM

The post advising me to check the transformer without a load wins. I thought I had done this, but I hadn't. Transformer is good.

Now all I have to do is figure out what the blank is wrong with this regulator. It's been a problem for a long time.

Thanks, all.


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