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 Post subject: radiola 82 aux input.
PostPosted: Jun Mon 10, 2019 11:59 pm 
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Joined: May Mon 27, 2019 3:18 am
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i have a radiola 82. its fully restored and working perfectly. i would like to add an aux input to it. it has a 5 terminal board on the back with the first 3 jumpered out. if i remove the jumper and connect a phone to terminals 3 and 5 i can get sound but its very very quiet. research tells me i need a transformer to up the signal. what kind of transformer should i use or should i use an amp. i attached a schematic with the terminals im talking about on the bottom left. Image


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Tue 11, 2019 12:42 am 
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Location: Dayton Ohio
according to the diagram, 3 and 5 should be jumpered with a 5000 ohm resistor and the signal fed in on 2 and 3.

You may need a transformer such as a 1-3 ratio type like a Stancor A53C. 10,000 ohm to 90,000 ohm step up.

https://www.tubesandmore.com/products/t ... tage-10-ma

Plus an additional volume control, unless you can control the volume from the signal source

-Steve

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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Tue 11, 2019 2:39 am 
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i just tried that. hooking to pins 2 and 3 with or without the resistor to pin 5 does nothing but cause a very loud hum. if i hook it to pins 3 and 5 i get sound but its very quiet. if you look on the other side of the diagram it shows where the wires go. it apears pin 5 goes to the 2nd detector tube. and pin 3 is ground. do you think the transformer would get me enough volume. i have a small amp i pulled out of an old ipod speaker. if i hook that up to pin 3 and 5 i get some more audio but not much. but its just a little ipod amp for 1 inch speakers.


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Wed 12, 2019 7:39 pm 
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what kind of potentiometer would i need for the aux input volume control using the transformer recommended. i will be using a phone or a bluetooth transmitter as the audio source.


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Wed 12, 2019 9:01 pm 
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well, you might try a higher ratio transformer such as an audio output transformer in reverse.

https://www.tubesandmore.com/products/t ... output-8-w

Connect the phone or bluetooth transmitter to the 16 ohm secondary tap and the radio on the 8000 primary tap.

A volume control should be on the radio side rather than the phono pickup side as shown in the schematic. a 50K probably would be optimal.

-Steve

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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Thu 13, 2019 6:41 am 
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ok thank you. i have not purchased any of the parts yet. would you recommend the 3 to 1 interstage transformer or the audio output transformer in reverse. i would like plenty of volume. with just a phone hooked up to it i get just a whisper of sound. could someone take another look at the schematic and tell me how to wire it. pin 2 apears to go to the grid of the 2nd detector. pin 5 goes to the cathode. do i hook to the cathode or the grid to get sound. if i hook to the grid i get nothing but a very loud hum. if i hook to the cathode i get a whisper of volume. if the schematic is correct does the audio signal and ground have to be hooked up a certain way or does it matter. i had the ground hooked to pin 3 ground and the signal to pin 2 or 5


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Thu 13, 2019 11:41 am 
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The audio output transformer in reverse will give the most gain. If the device you're using can drive a pair of headphones, it should work fine.
Plus you have a few taps to experiment with to get the levels right :)

On second though, try a 100K pot for the volume. Its not critical, but it may be a better match.

-Steve

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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Thu 13, 2019 5:05 pm 
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Location: Lexington, KY USA
Thanks for including a schematic. It might have been good to crop and reduce the width of the image a little before including it in the post. The wide image causes the text to run off the screen and requires a lot of scrolling. It is very clear at this size, though.

I think you want to follow the suggested circuit for use with a magnetic phono pickup. The
DPDT switch and 5000 ohm resistor can be the same as seen on the schematic.

An audio transformer may not be necessary, depending on your audio source.

For operation without a transformer, you can try putting a resistor across terminals 2 and 3,
then feeding your monaural audio through a capacitor to pin 2. The return for the audio
source is terminal 3. The resistor between 2 and 3 might be 470k, the capacitor 0.047uF.
You will probably want to include the suggested resistor between terminals 3 and 5. 4700
ohms is the modern value close to 5000.

The audio source must include a volume control, as the one on the radio only works for
radio stations.

If the volume is too low connected this way, you might want to try a step-up transformer.

Ted


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Sun 16, 2019 1:37 am 
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i got a chance to try that. with the resistor capacitor i get barely audible volume. i found an old audio output transformer thats measuring .1 ohm on the speaker side and .780 k ohm on the radio side. i tried that. it plays audible vocals but no bass. is this because the transformer is wrong for the application.


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Sun 16, 2019 2:08 am 
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Joined: May Mon 27, 2019 3:18 am
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heres what it sounds like on am. i dont know why the video quality is so low. it sounds much better in person. https://www.youtube.com/watch?v=76by5nq7W-Y&feature=youtu.be


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Sun 16, 2019 8:44 pm 
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Joined: Jan Tue 16, 2007 7:02 am
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Location: Lexington, KY USA
You might try a bypass cap across the added 5k resistor. The schematic shows one inside the chassis, but the value is unclear.
Something like 1uF. If electrolytic, put the positive end toward terminal 5.

What sort of audio source are you planning to use? There are several older threads about using a transformer. Find one that
uses a single transformer.

Ted


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Mon 17, 2019 1:46 am 
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Joined: May Mon 27, 2019 3:18 am
Posts: 49
i am planning to use a cell phone or bluetooth transmitter. i have at least 2 radios that will require a transformer to up the signal. planning to build a box holding the audio transformer, a volume control, a bluetooth transmitter and a switch to switch the transformer into and out of circuit. that way i can move it to whatever radio i feel like using. i would use an am transmitter but i want the highest quality sound and there is a lot of switch mode power supply interference in my house.


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Sun 30, 2019 3:27 pm 
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Try using 1 K resistor(s).
I use a 1:10 step-up ratio to get volume higher on the input.

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Burl Ives, RIP, oldtimer.
[:l>)


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Sun 30, 2019 4:06 pm 
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Using that PT-291 as shown would give you an approximate 11:1 ratio. The full winding would be about 22:1.

-Steve


Attachments:
p-t291_diagram.gif
p-t291_diagram.gif [ 15.18 KiB | Viewed 299 times ]

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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Sun 30, 2019 9:11 pm 
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Joined: May Mon 27, 2019 3:18 am
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i wired it up like that. using half the winding is not enough volume. using the full winding is ok volume. its kind of tinny though.
way to much high end. what do i have to mess with to get full clear sound like it plays on the radio. do i need to add that bypass cap.
(edit) added the 1uf bypass cap. doesnt seem to have done much. clipped a bit off the top end but now it sounds grainy.


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Sun 30, 2019 9:22 pm 
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I would try reducing the two 1000 ohm resistors (1 k) to maybe 100 ohms?

See if that does anything.

-Steve

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


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jun Sun 30, 2019 9:36 pm 
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Joined: May Mon 27, 2019 3:18 am
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tried 1k is almost inaudible. 100 is ok. i moved down to 1ohm to see what that was like. it plays nicely but its tinny and has way to much high end
i dont understand the schematic well enough to know what i have to do. i would like it to play as loudly and clearly as it does on radio
and i am willing to make some circuit modifications if i have to. adding a 1 uf bypass cap across the 5 k resistor on terminals 3 and 5 made the
volume control on the box i made more effective but made the sound a bit grainy. should i try going up on the cap. lower on the cap. the 5k resistor is
actually 4.7k. should i go up on that. do i need to add a resistor or cap elsewhere on the circuit. should i add a cap on the signal in on pin 2.


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 Post subject: Re: radiola 82 aux input.
PostPosted: Jul Mon 01, 2019 1:00 am 
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I looked at that drawing in the other thread but am replying here, try bypassing that volume control. Since volume is low, it is not needed.

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Burl Ives, RIP, oldtimer.
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