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 Post subject: Mystery Power Transformer
PostPosted: Oct Sat 14, 2017 7:10 pm 
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got this transformer to replace on in a Crosley "fiver"
HV winding with no center-tap
2 filament windings

Ran through the normal tests. No-load current is very low, and no sign of overheating
No-load voltages (input 125)
HV: 300 VAC
Fil 1: ~4.8 VAC
Fil 2: ~8 VAC

?????---If those are supposed to be for 5 and 6.3-volt tubes, then one is too low, and the other is too high
Am I missing something?

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 Post subject: Re: Mystery Power Transformer
PostPosted: Oct Sun 15, 2017 6:15 am 
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Location: Long Beach Ms. USA 39560
The lack of a HV center tap indicates that it is looking for a half-wave or bridge rectifier, which indicates it may have been designed after silicon diodes came into use.
You checked it with no load.
The 8 volt filament winding needs to be checked with the approximate load you expect.
Figure the total current ratings for all the tubes in your radio and put a load on it of the resistance that will draw that much current. The important voltage is at the tube pins.
4.8 volts seems close enough to me for one low-current 5 volt rectifier with short wire leads.
Good luck,
pat

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 Post subject: Re: Mystery Power Transformer
PostPosted: Oct Sun 15, 2017 7:10 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
Is it a 25 cycle radio ?

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de
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Steve Dow
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 Post subject: Re: Mystery Power Transformer
PostPosted: Oct Sun 15, 2017 7:21 am 
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I doubt if the transformer was designed for 25Hz---not enough iron.

The radio in question is 60Hz, and uses a single 5Y3 operating 1/2-wave (plates tied together):
http://www.nostalgiaair.org/pagesbymode ... 003375.pdf

I will try some tests under load.....

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"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Mystery Power Transformer
PostPosted: Oct Sun 15, 2017 7:58 am 
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pixellany wrote:
I will try some tests under load.....
Hi Mark,

Your unloaded rectifier winding being under-voltage worries me.
I fear there's a problem in the transformer.

- Leigh

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 Post subject: Re: Mystery Power Transformer
PostPosted: Oct Sun 15, 2017 8:49 am 
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Yes---we both are prone to "informed paranoia"....:)

I will test again for a possible shorted winding----in the "quick-check", there was no sign of getting even slightly warm with no load

What are we doing up at this ridiculous hour???

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 Post subject: Re: Mystery Power Transformer
PostPosted: Oct Sun 15, 2017 8:55 am 
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pixellany wrote:
What are we doing up at this ridiculous hour???
Talking to each other...

because everybody else is sleeping. ;-)

- Leigh

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 Post subject: Re: Mystery Power Transformer
PostPosted: Oct Sun 15, 2017 9:01 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
No-load voltages (input 125) -- It is listed as 117 on schematic

The filaments return to chassis on a 1 wire feed from transformer. Are all the filaments
reading 8 volts on the actual tube pins poking through the sockets.

Also there are many transformers listed, 60, 50, 25 Hz and one has a primary tap for
voltage selection.

Does the radio work well ?

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de
VE7ASO VE7ZSO
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Steve Dow
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 Post subject: Re: Mystery Power Transformer
PostPosted: Oct Sun 15, 2017 9:15 am 
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Radio has a bad PT.

The PT in question was acquired because it is exactly right mechanically, and seemed to have the required windings. (I would not be surprised if it is also for a Crosley----Until now, I've never seen a transformer set with 1/2-wave tube rectification)

Just found the part number: E-45923-B

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"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Mystery Power Transformer
PostPosted: Oct Mon 16, 2017 1:34 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
The half wave tube rectification was common right up to the end of tube era.
The design rational might be debated. Most of my peers from that era aren't
alive, and some wiser ones fled that trade, perhaps because the food was better
in different lines of work. :D

In the case of Philips, they had bags of their own patents and ways of doing things.

Attachment:
Philips Stereo from 1965.jpg
Philips Stereo from 1965.jpg [ 87.63 KiB | Viewed 592 times ]

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de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Mystery Power Transformer
PostPosted: Dec Fri 01, 2017 6:35 am 
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Well, I did a few more tests and did not find evidence of anything broken, so opened it up. First, put in a few loops of wire to measure the turns / volts constant. At 125V input, I got 5.4 turns / volt.
Next, peeled off a layer of paper to expose the winding that read 4.6 open-circuit. Counted the turns, it matched the 5.4 exactly. Next, removed that winding and counted the turns for the winding that measured 8.3 OC. Also 5.4 turns per volt.

Conclusion: transformer was working as designed.
I took off a few turns to get the one winding down to ~7.2 (for the 6.3-volt filaments), and then rewound the outer winding for ~5.5 volts OC for the 5v rectifier. It's back together, and has been tested at about 90% of full load with no issues. (Got only barely warm after 15 minutes). I missed the 5V slightly----at full load it's 4.8, which I have declared to be be close enough.

We may never know what the transformer was, but now it's on its way to save a Crosley Fiver.

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"It's always something". --Gilda Radner (1946 - 1989)


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