1930's Dual 55E Early Magnetic Reproducer Troubleshooting

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galacnor
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1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by galacnor » 14 Sep 2019 03:18

Hello everyone,

I'm currently restoring a 1930's phono-cabinet which is equipped with a Dual 55E. The cabinet is a little surprising in that it contains only the phonograph, no preamp, no speaker, no reciever, nothing, this appears to be how it came out of the factory and its starting to look more and more like I'll need a preamp for it despite what I'd expected.

I was under the impression that early electrical pickups didn't require any preamplification even if many people did have a preamplifier to adjust the equalization of the signal-as the tonearms of the time produced such a large soundwave on their own; but, I'm getting no audible signal out of the tonearm and maybe I got that entirely backwards!

I've taken apart the entire head, checked the rubber pieces to make sure they aren't perished, the magnet still retains its strength, the continuity of the coil by itself and of the entire apparatus together has been verified, I've even looked at the signal coming out of it on an Oscilloscope and it appears to be low, but still a healthy output. I've tried connecting the phonograph to the Magnetic Cart., Crystal Cart., and AUX inputs on a Steintron 57000R with no luck.

Is a flat preamp all I need to get in order to complete this project? Or do you all think there might be another malfunction that I haven't thought of?

Cheers, and if you need more information, just ask! I can upload a picture of the Oscilloscope if needed.

Alex

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by vanakaru » 14 Sep 2019 09:15

Are you sure the wires are good all the way to your amp. If you use ceramic/crystal cart you should hear something via AUX. But since you get nothing on any of these inputs I suspect wiring.

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by galacnor » 14 Sep 2019 10:45

vanakaru wrote:
14 Sep 2019 09:15
Are you sure the wires are good all the way to your amp. If you use ceramic/crystal cart you should hear something via AUX. But since you get nothing on any of these inputs I suspect wiring.
Hello!

Thanks for the reply.

I can always change the wires out but im getting continiuty and a signal down them. Is it possible they might still have a fault? If so, i can definitely replace them easily.

Cheers
Alex

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by nat » 14 Sep 2019 13:12

I've read that some early Rochelle salt/ceramic/crystal/piezo cartridges produced enough output to power a speaker directly. But that probably would be a speaker of unusual impedance, and it would have been at very high tracking forces (by current standards). And Rochelle salts, at least, can degrade over time - I have the impression that they can absorb moisture and more or less dissolve themselves. Regardless, use a meter to see if the problem is the cartridge, not the wires.

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by circularvibes » 14 Sep 2019 16:32

The early magnetic cartridges, like the horse shoe type, would lose output if the magnet is demagnetised. I know there is a way to remagnetise them, but you would have to search antique radio forums for that method. They would have been used with contemporary radios with a two wire input, The original plug would have likely been a two prong bakelite piece. I would try to find a contemporary radio with phono input to try it.

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by vanakaru » 14 Sep 2019 16:51

Loosing magnet may be good bet. If there is no magnet or if it is weak you hear nothing but the coils and wires check out fine. The easiest to test this theory is the get contemporary Neodymium magnet and attach it to existing one or just to the metal part of the body. These come with various sises so you may be able to find suitable one to permanently remedy the cartridge.

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by galacnor » 15 Sep 2019 03:39

circularvibes wrote:
14 Sep 2019 16:32
The early magnetic cartridges, like the horse shoe type, would lose output if the magnet is demagnetised. I know there is a way to remagnetise them, but you would have to search antique radio forums for that method. They would have been used with contemporary radios with a two wire input, The original plug would have likely been a two prong bakelite piece. I would try to find a contemporary radio with phono input to try it.
Hello!

Thanks for the suggestion, unfortunately the magnet and coil were among the first things I checked, the magnet is still extremely strong as far as I can tell, and it attracts anything magnetic that I throw at it, including the screws in the pickup, which made reassembling the head after I completed my servicing quite a frustrating experience!

In regards to the kind of plug that it originally had, it was originally equipped with a 3 prong kind of guy-with the left most and right most prongs being used to complete the circuit the mono audio passed through, and the middle prong being for grounding. From what I understand, it was a standard on radio sets for some time, at least in Germany and maybe in other places. I have a Tefifone and a Meersburg 8 Automatic that both have the same connection. Its a shame that the Meersburg 8 isn't operational at this point, thats a repair job for a whole other day! All in all, being that the original plug is long gone and was replaced with a DIN-5, I plan on replacing the DIN-5 with an RCA and running that into a preamp and then running the preamp into a receiver which is also DIN-5 based with an RCA to DIN-5.

https://i44.photobucket.com/albums/f49/ ... jyqzpv.jpg
vanakaru wrote:
14 Sep 2019 16:51
Loosing magnet may be good bet. If there is no magnet or if it is weak you hear nothing but the coils and wires check out fine. The easiest to test this theory is the get contemporary Neodymium magnet and attach it to existing one or just to the metal part of the body. These come with various sises so you may be able to find suitable one to permanently remedy the cartridge.
I was also hopeful that it would be a problem with the magnet, but, i went through the entire head and redid everything, checked the rubber bits, the magnet, coil, everything. The head seems to be outputting and getting the signal out the cable coming out from it. I'm not against trying a new magnet, but, at the moment I'm convinced that this is probably not the solution. Right now I'm just hoping that its only missing a preamp; but, for some reason I'm also doubting that, too! I've scoped the signal coming out of it. Seems on par with the kind of signal you see coming out of a modern cartridge before it goes through a preamp, so I wonder whats going on! Check out the attached image.
nat wrote:
14 Sep 2019 13:12
I've read that some early Rochelle salt/ceramic/crystal/piezo cartridges produced enough output to power a speaker directly. But that probably would be a speaker of unusual impedance, and it would have been at very high tracking forces (by current standards). And Rochelle salts, at least, can degrade over time - I have the impression that they can absorb moisture and more or less dissolve themselves. Regardless, use a meter to see if the problem is the cartridge, not the wires.
I have also heard about these things and thats why I'm so puzzled by this pickup's relatively low output. The good news is that this is a magnetic pickup so it won't suffer from the same crystal degradation of the piezo electrics and others.

I've put the output cable from the pickup on an oscilloscope and it seems to be emitting a signal with a strength on par with a modern cartridges (see the attached image), so perhaps all it really needs is a preamp. Any further thoughts?

Heres the picture of the signal coming out:

https://i44.photobucket.com/albums/f49/ ... 8qv8ak.png

Cheers

Alex

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by circularvibes » 15 Sep 2019 04:17

Hi There! I haven't seen the three prong plug before. The two prong was the same without the middle spade. I have seen the two prong plug on table radios and consoles from the 1950's back to the 1920's. The main difference is the later radios would have taken a ceramic or crystal cartridge with much higher output. If you can come up with a Telefunken or similar table radio from the 1930's you will likely find what you need. From your references I suspect you are in Germany. Those plugs would have also been in Eastern European radios as well such as Russia. I have a feeling that it won't perform as originally intended with a modern preamp. If you research the schematics from radios of that period, you might find you can assemble a preamp of the right vintage.

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by galacnor » 15 Sep 2019 04:59

circularvibes wrote:
15 Sep 2019 04:17
Hi There! I haven't seen the three prong plug before. The two prong was the same without the middle spade. I have seen the two prong plug on table radios and consoles from the 1950's back to the 1920's. The main difference is the later radios would have taken a ceramic or crystal cartridge with much higher output. If you can come up with a Telefunken or similar table radio from the 1930's you will likely find what you need. From your references I suspect you are in Germany. Those plugs would have also been in Eastern European radios as well such as Russia. I have a feeling that it won't perform as originally intended with a modern preamp. If you research the schematics from radios of that period, you might find you can assemble a preamp of the right vintage.
Hello,

You are correct. I'm in Germany! I'm a transplant from Ohio, though. Came here for university a few years back, met a girl, got married, the standard kind of snafu many young men get into! The Dual phonograph was actually her grandfathers and has been living in her grandparents old house in storage for years, its now our house and during renovations I found him neglected in a storage room and brought him out to stretch his legs. Its a wartime model so the cabinet isnt of the best wood; but, somehow the turntable itself is a beast of a machine and is heavier than the cabinet is when the two are separated. The turntable and cabinet are both interesting and well designed. Theres a queuing light for the turntable, a light for the cabinet underneath, and both automatically turn on and off depending on if the cabinet/turntable "drawer" is opened or closed and they function independently of each other, the head turns over to make changing needles a breeze, and the table has auto stop which is pretty slick for the era.

https://i44.photobucket.com/albums/f49/ ... b1usgb.jpg

I never saw a plug like the one thats missing before i moved here, either. Weird little guy.

I've considered doing as you talk about and finding something period to pair with it. I think about picking up a Volksampfanger which has a phono in on it. They're period, relatively cheap, easy to work on, and will get the job done. I'm sad to say I havent turned up much documentation on the impedance of the pickup or what it wants to work with, so im grasping at straws and just testing anything i can find with it. I figure even if it doesn't sound good a cheap little preamp modified to not apply RIAA will at least give me somewhere to start, but I could be wrong!

We will see what happens. It would be really neat to put together a copy of a vintage preamp for it.

Cheers to you!
Alex

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by 62vauxhall » 15 Sep 2019 05:12

I have to ask, since you claim signal trace on a scope, how much voltage is it producing? "Scratching" the needle across fingerprint ridges should, in my mind, create the maximum output in it's present condition.

You said "on par with a modern cartridge"?

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by circularvibes » 15 Sep 2019 05:12

That is a beautiful turntable Alex. Have you asked what it was hooked to originally? It may still be around but needing a bit of repair. I would have rescued it too! You might try your local library for old schematics. Anything pre WW2 should be appropriate. Those magnetic cartridges went out of favour by the 1940's. Crystal pickups were so cheap to produce. One word of warning with your pickup, never drop it on the record or the motorboard. A shock can be enough to damage the magnetic output or crack the magnet. That was the main reason period technicians had to remagnetise the pickups. They used to have a device for that but most are lost to time. I really hope you get the Dual going, it is a real showpiece.

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by galacnor » 16 Sep 2019 01:50

62vauxhall wrote:
15 Sep 2019 05:12
I have to ask, since you claim signal trace on a scope, how much voltage is it producing? "Scratching" the needle across fingerprint ridges should, in my mind, create the maximum output in it's present condition.

You said "on par with a modern cartridge"?
Please see the video of the scope here-https://youtu.be/RSKsAKmBJWg
I believe its tracing around 10mV/s.

I have already done a little "scratching" with my finger on the needle while the entire apparatus is hooked up to the scope, I believe you are correct in your belief that it is at the height of its output then.

in regards to "on par with a modern cartridge",
I measured a modern phonograph with an LP cartridge and stylus and it also measured about 10mV/s while tracking, which is leading me to believe that we need a preamp!

Any thoughts?
circularvibes wrote:
15 Sep 2019 05:12
That is a beautiful turntable Alex. Have you asked what it was hooked to originally? It may still be around but needing a bit of repair. I would have rescued it too! You might try your local library for old schematics. Anything pre WW2 should be appropriate. Those magnetic cartridges went out of favour by the 1940's. Crystal pickups were so cheap to produce. One word of warning with your pickup, never drop it on the record or the motorboard. A shock can be enough to damage the magnetic output or crack the magnet. That was the main reason period technicians had to remagnetise the pickups. They used to have a device for that but most are lost to time. I really hope you get the Dual going, it is a real showpiece.
Thank you for the compliment!

I've talked to my father in law about it and he had some kind of hand made amp attached to it, which is why he chopped the 3 prong off and added the DIN-5. He's not sure where it is; but, maybe it will turn up and I can do some testing with it.

Before that, it was hooked directly into the Seeburg 8, but, thats not working right now, unfortunately!

I think it was hooked into something else way back in the 30's and 40's; but, thats something I don't think I'll ever find out unless I find some old photos with it in the background.

I've heard about all the stories with the fragility of the magnetic pickups-and I'm really surprised this one is still magnetized, its almost unbelievable.

Showpiece! Again, I appreciate the compliment! I also hope that I get it running, and there will be some pictures and video of it to come once its running properly.

Regards
Alex

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by 62vauxhall » 16 Sep 2019 03:32

With 10mv being produced and fed into a phone preamp and no audio signal being amplified, that would have me scratching my head too. To me that doesn't quite seem possible.

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by circularvibes » 16 Sep 2019 03:38

Hi Alex, if you are getting 10mV then you should be good to add an RCA plug and go straight into the phono input of any modern receiver. I do not think you should have any problems. It won't be a crystal type output of 1 V or more so an auxilliary or tape input won't work. You will have RIAA equalisation but that shouldn't be too bad if you play 1940's and newer records. Any deficiencies could be handled with tone controls. Only acoustic records should need flat input but can sound more pleasant with other EQ curves. If possible, use a new cable for the RCA and see if there is a mute switch under the chassis. I doubt there is a mute but can't rule it out. I see a knob on the player, is it possible to be a volume control or just for power? Some machines used a rheostat for output control.

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Re: 1930's Dual 55E Early Magnetic Reproducer Troubleshooting

Post by galacnor » 16 Sep 2019 11:41

62vauxhall wrote:
16 Sep 2019 03:32
With 10mv being produced and fed into a phone preamp and no audio signal being amplified, that would have me scratching my head too. To me that doesn't quite seem possible.
You and me both are quite confused! I'm considering replacing the cable running from the tonearm to the amp, to me this is one of the last things I could do to remedy my problem with the head being known good at this point. I'm getting pretty annoyed by this crazy thing!
circularvibes wrote:
16 Sep 2019 03:38
Hi Alex, if you are getting 10mV then you should be good to add an RCA plug and go straight into the phono input of any modern receiver. I do not think you should have any problems. It won't be a crystal type output of 1 V or more so an auxilliary or tape input won't work. You will have RIAA equalisation but that shouldn't be too bad if you play 1940's and newer records. Any deficiencies could be handled with tone controls. Only acoustic records should need flat input but can sound more pleasant with other EQ curves. If possible, use a new cable for the RCA and see if there is a mute switch under the chassis. I doubt there is a mute but can't rule it out. I see a knob on the player, is it possible to be a volume control or just for power? Some machines used a rheostat for output control.
I think i'm about to take your advice and add an RCA to the end of a new wire going from the tonearm, that way we can eliminate that as a source of problems. Even though I'm getting continuity, I don't entirely trust that anymore as a certification that things are working correctly!

Are you speaking of that knob shaped thing in-front of the tonearm? That indeed spins back and forth and also doubles as a used needle dish. I don't believe that its connected to anything; but, I will take the player apart again and take a look. Results coming later today!

Alex

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