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 Post subject: GE Record player Bad output transformer
PostPosted: Nov Thu 07, 2019 11:18 pm 
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Joined: Nov Thu 07, 2019 11:11 pm
Posts: 41
I recently acquired a ge-rp-1590a however after recapping i find it is emitting a terrible smell and one output transformer is extremely hot.
I need to know the best replacement for it as it is worrisome that it is getting this hot. It is right next to the rectifier tube which is also getting hot but this transformer is getting hot enough i worry it will catch fire the specs are 6000 ohm primary 6-8 ohm secondary and it is ge part number rs2716.
I would appreciate any help on this
I just measured the transformer out of the circuit primary is at 15 ohms vs 6000 ohm ohm on the parts list and 500 ohm on the schematic
also there is a hum


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 2:57 am 
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Update the good transformer on the other channel measures 500 ohms on the primary


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 3:47 am 
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500 ohms is about right for the DC resistance. The 6000 ohm value is the impedance and applies only when the secondary load is as specified. IOW, the transformer provides an impedance ratio (AKA transformation)--this is not something we normally measure.

A low DC resistance reading on an output transformer primary is not very common, and suggests that something has failed catestrophicically. To confirm, measure the DC resistance with the transformer disconnected from the circuit.

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 11:34 am 
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The 15 ohm measurement is out of circuit i was fooled into thinking it was good at first by measuring in circuit where i got 1500 ohms
I have found an replacement that ge claims worked back in the day
a stancor a-3337 off of vivatubes for 50


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 12:49 pm 
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Generally speaking, output transformers don't typically go bad in the way you are describing.
Something else may be causing the transformer to get too hot, such as the output tube its attached to conducting too hard.

Have you replaced the .01uf coupling capacitor between the preamp and the output tube? If it is leaky, it could cause your problem.

-Steve

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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 2:09 pm 
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Joined: Nov Thu 07, 2019 11:11 pm
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I am certain the coupling capacitor or the 7189a tube is not at fault what may have happened is when the saler plugged it in to test with the bad electrolytics in it and a bad ground on that speaker caused the transformer to short out.
All other caps are either cera
mic or mica which are not known for failing.
Not to mention prior to discovering the scalding shorted transformer i figured it was a bad tube so i swapped the tubes that transformer was still hot it didn't follow the left tube however if i removed the left tube from circuit the transformer no longer gets hot


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 6:49 pm 
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A shorted (low-resistance) winding won't make it get hot - but a short to the core (ground) definitely will. And if there's a capacitor from the output tube plate to ground, it's an immediate suspect.

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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 7:06 pm 
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Location: Urbana, Illinois
Are you certain it isn't the power transformer that gets too hot?
There are 3 transformers in total.
The largest one is the power transformer.
The 2 smaller transformers are the left channel audio output transformer and the right channel audio output transformer. Both of these are exactly the same size.

A simple test for the power transformer is to remove the 5Y3 rectifier tube, then power up the amplifier. Nothing should get hot.

I use a Kill-A-Watt (cost: $20) to measure the power consumption of radios/amplifiers where I suspect something is shorted or failed.
The standard power consumption of your unit with everything working correctly is 62 watts, 0.6 amps.
With the 5Y3 removed, this should drop to perhaps 15 to 20 watts.
If you remove ALL of the tubes, then it should drop even lower, perhaps <10 watts.
There will also be a difference depending on whether the turntable motor is running or not. The turntable motors usually consume about 5-10 watts.

If the power transformer still gets very hot very fast, with all of the tubes removed, then it is faulty and must be replaced.

-EB


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 7:32 pm 
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Joined: Nov Thu 07, 2019 11:11 pm
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I am certain its the left audio output tube its the small one beside the 5y3 I also have had a shorted coil get hot fast especially if the coil is not only shorted to itself but the case or core which is grounded to the chassis.
What I suspect happened to fry it was as follows the saler bought at auctuon plugged it in to try it found the weak left channel and sold it on ebay. When plugged it in with the leaky filter caps and the bad left channel ground for the speaker it caused that audio output transformer to suddenly be shorted to ground on the primary through the bad filter cap which was clearly budged out when i got and also turn into a choke


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 8:17 pm 
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Joined: Nov Thu 07, 2019 11:11 pm
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Also from i know of transformers is that if you have a transformer rated for a certain voltage. It will have a certain number of turns of a certain size wire. Then if anything should happen to make that length of wire shorter ie a short developes and then you try to put the same amount of voltage into the damaged transformer as you did the undamaged one it will run hot.
Also keep in mind here it is rated at 500 ohms on the primary and measures 15 ohms that is no small short it has lost 485 ohns somewheres and the 7189a tube feeding it has no way of knowing this so it still pumps the full signal in hence it runs hot


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 9:45 pm 
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My apologies, I somehow missed reading you measured 15 ohms on the primary.

-Steve

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-Zenith
-Sparton
-Pre-War FM
Consoles and floor models, the bigger, the better!


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Fri 08, 2019 10:08 pm 
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Try this test:
Completely disconnect both primary wires that go to the failed output transformer. One of these primary wires is connected to the B+ power supply rail. The other primary wire is connected to the plate of the 7189 tube. Disconnect both of these wires and tape them up.
For this test, the secondary wires of the failed output transformer don’t matter whether they are still connected or not (there are no DC power supply voltages on the secondary).

Then temporarily connect a 500 ohm 10 watt resistor between B+ and the plate of the 7189 tube for the bad channel. This resistor acts as a temporary substitute for the failed output transformer.

The amplifier should then play normally on the other channel without anything overheating.

Of course there will be no sound heard from the speaker for the channel without its output transformer.
But the other channel should play and should sound good.

For an additional test of the failed output transformer, measure both its primary and secondary DC resistance while it is entirely disconnected from the rest of the amplifier. For this test, all wires of the faulty transformer, both primary and secondary, must be disconnected. In addition, measure for any DC resistance between the primary wires and the metal case of the transformer. This should measure as “open circuit” - infinite resistance. Also measure for any resistance between primary and secondary. Again, this should be open circuit, infinite resistance.

As mentioned in another post, it is possible that the primary winding shorted out to the metal case of the transformer. It is also possible for a transformer to develop an internal short circuit between primary and secondary.

If you confirm the output transformer failed, unfortunately I doubt you will be able to find an exact original factory replacement. But there may be a Hammond brand audio output transformer available that has the correct specs. It needs to be “single ended” with about 6000 ohms primary impedance and rated for >=5 watts of audio output power.

-EB


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Sat 09, 2019 2:11 am 
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Joined: Nov Thu 07, 2019 11:11 pm
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Just checked the secondary got 640 ohms on it schematic calls for .8 checked between the secondary and primary and they are connected together at 400 ohms.
Also I now have a stancor a-3337 from viva tubes coming which according to the parts list is the same as the oem transformer. Probably the only one around anymore
Now I see what through me off i was checking the secondary and got 15 ohms and the primary has 500 ohms like it should however it is shorted together if only marginally.
also i checked the 2 ceremic .01 mfd caps and they are both fine no short


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Sat 09, 2019 6:29 pm 
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SpaceFerret42 wrote:
Just checked the secondary got 640 ohms on it schematic calls for .8 checked between the secondary and primary and they are connected together at 400 ohms.
Shorts between primary and secondary are relatively common in audio output transformers. This is the fault that your transformer has.

A good audio output transformer typically has 200-800 ohms primary resistance, <2 ohms secondary resistance, and a totally open circuit (infinite ohms) between primary and secondary. Measurement between transformer frame and primary should always have infinite resistance. Sometimes (but not always) one end of the secondary is connected to the transformer frame on purpose.

Quote:
Also I now have a stancor a-3337 from viva tubes coming which according to the parts list is the same as the oem transformer. Probably the only one around anymore
Now I see what through me off i was checking the secondary and got 15 ohms and the primary has 500 ohms like it should however it is shorted together if only marginally.
also i checked the 2 ceremic .01 mfd caps and they are both fine no short
Please let us know how well the replacement output transformer works. It should be fine.

-EB


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Wed 13, 2019 2:38 am 
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Joined: Nov Thu 07, 2019 11:11 pm
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The new transformer works well.
now i have to worry about the bad speaker.
plus what would cause a whistle at low volume?


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Wed 13, 2019 3:34 am 
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Joined: Jan Wed 16, 2013 12:04 am
Posts: 1618
Location: 77001
SpaceFerret42 wrote:
what would cause a whistle at low volume?

Make sure the 12AX7 tube socket is cleaned well, and
clean the tube pins of oxidation.
You may want to sub another known good 12AX7, if whistle persists,
after cleaning.
H


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Wed 13, 2019 12:30 pm 
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Joined: Nov Thu 07, 2019 11:11 pm
Posts: 41
Fair point will have to try the cleaning and if it persists purchase of new tubes.
How does one clean the tiny 12ax7 socket holes the pipe cleaner or q-tip method seems to big?


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Wed 13, 2019 4:11 pm 
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Joined: Jan Wed 16, 2013 12:04 am
Posts: 1618
Location: 77001
SpaceFerret42 wrote:
Fair point will have to try the cleaning and if it persists purchase of new tubes.
How does one clean the tiny 12ax7 socket holes the pipe cleaner or q-tip method seems to big?

The 12AX7 may be in a phenolic mount, which can be degraded by
de-oxit and other cleaners.

People here recommend to spray or dip the pins of the tube with cleaner,
insert tube into socket, remove and wipe off pins.

Repeat several times, and wipe off any residue on the phenolic socket,
top and bottom.
H


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Wed 13, 2019 4:32 pm 
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Joined: Nov Thu 07, 2019 11:11 pm
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That actually might work have to try plus i never use deoxit or other harse cleaners as find rubbing alcohol works well and easier for me to get as i have to get other cleaners from web


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 Post subject: Re: GE Record player Bad output transformer
PostPosted: Nov Wed 13, 2019 5:05 pm 
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Location: Urbana, Illinois
SpaceFerret42 wrote:
The new transformer works well.
now i have to worry about the bad speaker.
plus what would cause a whistle at low volume?
This amplifier circuit uses “negative feedback” which is obtained from the secondary of the output transformer.

Depending on how the new replacement output transformer is connected, this feedback could be either “negative” or “positive.”

Positive feedback turns the audio amplifier circuit into an OSCILLATOR. (We don’t want this). This could be the source of the “whistle.”

Therefore, you should temporarily reverse the polarity of the 2 wires that connect to EITHER the primary OR the secondary of the replacement output transformer. Reverse the connections ONLY on one side, either the primary or the secondary. Not both sides.

The correct connection should not whistle. And there should be no oscillation visible when testing the circuit with an oscilloscope.

Another way to test: Connect AC voltmeter across secondary of output transformer. With amplifier turned on and the volume control at a low level setting but without a record playing on the turntable, there should be very little AC voltage. If it is oscillating, there would be >1V of AC, and this unwanted AC voltage might be largest when the volume control is near minimum.

When output transformer is wired correctly (for negative feedback) the AC voltage at output transformer secondary should remain very low for all settings of the volume control.

Then, when you are playing a record, there will be a varying AC voltage here that gets larger when you crank up the volume. But when you lift the needle from the record, the AC voltage should drop to a very low value ( <200mV ).

-EB


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