Low resistance in power transformer secondary
« on: July 01, 2020, 08:47:18 AM »
Hello DIYers!

A quick advise needed please.. i have an old tube amp as my next project. Starting with my power transformer.

Secondary should measure 300Ohms and 330 Ohms to ground according to the schematic drawings but I am not nearly there.. i am getting 200 Ohms and 220Ohms..

This means that this transformer going downhill?  Approx 50-60 years old transformer..?

Many thanks for the advise. !


JohnRoberts

Re: Low resistance in power transformer secondary
« Reply #1 on: July 01, 2020, 09:23:27 AM »
Hello DIYers!

A quick advise needed please.. i have an old tube amp as my next project. Starting with my power transformer.

Secondary should measure 300Ohms and 330 Ohms to ground according to the schematic drawings but I am not nearly there.. i am getting 200 Ohms and 220Ohms..

This means that this transformer going downhill?  Approx 50-60 years old transformer..?

Many thanks for the advise. !
I wouldn't expect a graceful drop in resistance over years. A possible failure mode is an insulation breakdown that causes nearby turns to short with each other. I would not expect a 33% drop in resistance from that failure vector.

Can you test the transformer functionally?

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: Low resistance in power transformer secondary
« Reply #2 on: July 01, 2020, 01:13:21 PM »
I wouldn't expect a graceful drop in resistance over years. A possible failure mode is an insulation breakdown that causes nearby turns to short with each other. I would not expect a 33% drop in resistance from that failure vector.

Can you test the transformer functionally?

JR

Hey JR

Thanks for the note. I would need to wait a couple of days until I can fire it up... there is a special 2 prong cable I would need and I don't have it  yet.

I went through this  very nice little amp (attached) and besides the wax foil capacitors, everything else are pretty much within 15% +/- specs...


EmRR

Re: Low resistance in power transformer secondary
« Reply #3 on: July 01, 2020, 02:14:55 PM »
If they had another vendor wind transformers it could account for it.  I expect it’s fine. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

JohnRoberts

Re: Low resistance in power transformer secondary
« Reply #4 on: July 01, 2020, 03:54:23 PM »
If they had another vendor wind transformers it could account for it.  I expect it’s fine.
+1... I'm not the transformer guy here...

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: Low resistance in power transformer secondary
« Reply #5 on: July 03, 2020, 01:09:37 PM »
Thanks guys for the suggestions. Will go through and check the other components and turn it on in order to see /check the voltages...  :)


 

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