Hello,

Thanks to some tips I found on this site I finally have my 6V Bendex radio playing again. Basically all it needed was the points in the vibrator to be cleaned, which I accomplished by passing 120V AC through it with a 40W bulb in series for a minute or so - I still can't believe this worked! I also replace all the paper and the three eloctrolytic caps (which I installed backwards first! the negative end goes to the ground, which is positive on this radio...) as a matter of course. Not knowing when to leave well enough alone, I am considering adding an aux input to this radio. Here is the schematic:

http://www.nostalgiaair.org/PagesByModel/387/M0002387.pdf

My understanding is that it should be connected to some of the wires going to the volume control, but I'm not sure which ones? Also, I believe a switch has to be put in to cut off the circuit to another part of the radio but again I'm pretty clueless?

Alternatively I could use a small AM transmitter but am I correct in assuming I would get worse sound quality?

http://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html

Thanks in advance for any input, Ken

:Hello,
:
:Thanks to some tips I found on this site I finally have my 6V Bendex radio playing again. Basically all it needed was the points in the vibrator to be cleaned, which I accomplished by passing 120V AC through it with a 40W bulb in series for a minute or so - I still can't believe this worked! I also replace all the paper and the three eloctrolytic caps (which I installed backwards first! the negative end goes to the ground, which is positive on this radio...) as a matter of course. Not knowing when to leave well enough alone, I am considering adding an aux input to this radio. Here is the schematic:
:
:http://www.nostalgiaair.org/PagesByModel/387/M0002387.pdf
:
:My understanding is that it should be connected to some of the wires going to the volume control, but I'm not sure which ones? Also, I believe a switch has to be put in to cut off the circuit to another part of the radio but again I'm pretty clueless?
:
:Alternatively I could use a small AM transmitter but am I correct in assuming I would get worse sound quality?
:
:http://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html
:
:Thanks in advance for any input, Ken

Ken H:
Using a small AM transmitter would certainly compromise the sound quality over running direct to the volume control. To use the audio section of the radio as an amplifier only, do this: Locate the wire that runs from the 2nd IF transformer to the volume control, and remove it. I don't know exactly what you want to do, but you need to connect a SPDT toggle switch, with one side to the IF transformer, and the common to the volume control. The other side of this switch goes to the jack you plug your external audio. You will, of course, not have stereo, so use a stereo jack and connect the two sides together. The wire connecting the radio to the jack and switch panel (assuming you want to place it under the dash) has to be shielded.

You might can get a jack that will automatically disconnect the radio when the external is plugged in, just like a headphone jack.

Lewis

Thanks Lewis, I will give it a shot! Ken

::Hello,
::
::Thanks to some tips I found on this site I finally have my 6V Bendex radio playing again. Basically all it needed was the points in the vibrator to be cleaned, which I accomplished by passing 120V AC through it with a 40W bulb in series for a minute or so - I still can't believe this worked! I also replace all the paper and the three eloctrolytic caps (which I installed backwards first! the negative end goes to the ground, which is positive on this radio...) as a matter of course. Not knowing when to leave well enough alone, I am considering adding an aux input to this radio. Here is the schematic:
::
::http://www.nostalgiaair.org/PagesByModel/387/M0002387.pdf
::
::My understanding is that it should be connected to some of the wires going to the volume control, but I'm not sure which ones? Also, I believe a switch has to be put in to cut off the circuit to another part of the radio but again I'm pretty clueless?
::
::Alternatively I could use a small AM transmitter but am I correct in assuming I would get worse sound quality?
::
::http://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html
::
::Thanks in advance for any input, Ken
:
:Ken H:
:Using a small AM transmitter would certainly compromise the sound quality over running direct to the volume control. To use the audio section of the radio as an amplifier only, do this: Locate the wire that runs from the 2nd IF transformer to the volume control, and remove it. I don't know exactly what you want to do, but you need to connect a SPDT toggle switch, with one side to the IF transformer, and the common to the volume control. The other side of this switch goes to the jack you plug your external audio. You will, of course, not have stereo, so use a stereo jack and connect the two sides together. The wire connecting the radio to the jack and switch panel (assuming you want to place it under the dash) has to be shielded.
:
:You might can get a jack that will automatically disconnect the radio when the external is plugged in, just like a headphone jack.
:
:Lewis
:
:
:
:

:Thanks Lewis, I will give it a shot! Ken
:
:::Hello,
:::
:::Thanks to some tips I found on this site I finally have my 6V Bendex radio playing again. Basically all it needed was the points in the vibrator to be cleaned, which I accomplished by passing 120V AC through it with a 40W bulb in series for a minute or so - I still can't believe this worked! I also replace all the paper and the three eloctrolytic caps (which I installed backwards first! the negative end goes to the ground, which is positive on this radio...) as a matter of course. Not knowing when to leave well enough alone, I am considering adding an aux input to this radio. Here is the schematic:
:::
:::http://www.nostalgiaair.org/PagesByModel/387/M0002387.pdf
:::
:::My understanding is that it should be connected to some of the wires going to the volume control, but I'm not sure which ones? Also, I believe a switch has to be put in to cut off the circuit to another part of the radio but again I'm pretty clueless?
:::
:::Alternatively I could use a small AM transmitter but am I correct in assuming I would get worse sound quality?
:::
:::http://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html
:::
:::Thanks in advance for any input, Ken
::
::Ken H:
::Using a small AM transmitter would certainly compromise the sound quality over running direct to the volume control. To use the audio section of the radio as an amplifier only, do this: Locate the wire that runs from the 2nd IF transformer to the volume control, and remove it. I don't know exactly what you want to do, but you need to connect a SPDT toggle switch, with one side to the IF transformer, and the common to the volume control. The other side of this switch goes to the jack you plug your external audio. You will, of course, not have stereo, so use a stereo jack and connect the two sides together. The wire connecting the radio to the jack and switch panel (assuming you want to place it under the dash) has to be shielded.
::
::You might can get a jack that will automatically disconnect the radio when the external is plugged in, just like a headphone jack.
::
::Lewis

Ken:
Looking more carefully at the schematic, I see a resistor in the circuit. Leave it alone, and just have the volume control connected to the common of the switch. Everything else goes to the "radio" side of the switch, so that when you are in the "external" position, your tape, CD, Ipod, etc. is connected to the volume control and nothing else

Lewis

I did this to my 1949 Mercury radio (in my 1951 Chevrolet). CDs sound nice. However I have found that mixing channels on solid state devices can cause distortion. You are better off mixing the two channels through 50-100K resistors (for the "hot" wires, not the ground wires....they can usually be tied together, since they always are with a headphone plug anyway).

Another thing I did which is optional, of course, is put the RF filaments on the switch. In that case I was using a DPDT switch. Thrown one way the radio was connected to the amp, and the filaments of the RF tubes lit up. Thrown the other way they were disconnected, and the aux jack was connected. That saved me a little extra power, which, in a 1951 Chevrolet, is hard to come by. Now I have it running with a 90 ampere alternator regulated at 7.4 volts, so I have no problems with accessories. With the old 35 amp. generator, extra juice was little.

T.

:I did this to my 1949 Mercury radio (in my 1951 Chevrolet). CDs sound nice. However I have found that mixing channels on solid state devices can cause distortion. You are better off mixing the two channels through 50-100K resistors (for the "hot" wires, not the ground wires....they can usually be tied together, since they always are with a headphone plug anyway).
:
:Another thing I did which is optional, of course, is put the RF filaments on the switch. In that case I was using a DPDT switch. Thrown one way the radio was connected to the amp, and the filaments of the RF tubes lit up. Thrown the other way they were disconnected, and the aux jack was connected. That saved me a little extra power, which, in a 1951 Chevrolet, is hard to come by. Now I have it running with a 90 ampere alternator regulated at 7.4 volts, so I have no problems with accessories. With the old 35 amp. generator, extra juice was little.
:
:T.

Good idea, T. I got my experience when 45 RPM just came out, and RCA made a little record changer for 45 only. I adapted many a AA5 in some teenybopper bedroom to let her play the 45s (say Elvis) through her bedroom radio. My hormones hadn't kicked in yet, so the only reward I got was having all the girls smooching up to me while all the football players (who used to be the heroes) watched.
Lewis

Well, this worked successfully. I used a closed-circuit 1/8" phone jack from Radio shack (274-246) so that when nothing is plugged in, the normal AM circuit is complete from t2 to the volume knob. When something is plugged the connection back to t2 gets cut off.

Right now it seems to work ok without resistors. Are you saying that the right and left channels from the ipod should each pass through a 50-100k resistor before being connected together? Will this reduce the volume?

Thanks again, Ken H

::I did this to my 1949 Mercury radio (in my 1951 Chevrolet). CDs sound nice. However I have found that mixing channels on solid state devices can cause distortion. You are better off mixing the two channels through 50-100K resistors (for the "hot" wires, not the ground wires....they can usually be tied together, since they always are with a headphone plug anyway).
::
::Another thing I did which is optional, of course, is put the RF filaments on the switch. In that case I was using a DPDT switch. Thrown one way the radio was connected to the amp, and the filaments of the RF tubes lit up. Thrown the other way they were disconnected, and the aux jack was connected. That saved me a little extra power, which, in a 1951 Chevrolet, is hard to come by. Now I have it running with a 90 ampere alternator regulated at 7.4 volts, so I have no problems with accessories. With the old 35 amp. generator, extra juice was little.
::
::T.
:
:Good idea, T. I got my experience when 45 RPM just came out, and RCA made a little record changer for 45 only. I adapted many a AA5 in some teenybopper bedroom to let her play the 45s (say Elvis) through her bedroom radio. My hormones hadn't kicked in yet, so the only reward I got was having all the girls smooching up to me while all the football players (who used to be the heroes) watched.
:Lewis

It shouldn't reduce volume, since not much loading takes place at the audio input.

Connect the two channels together and listen to music with a lot of crisp treble. Listen with both channels connected, and then just one. See if you notice a difference. Sometimes the treble can sound raspy. It all depends on the design of the CD player or Ipod's output.

T.

:Well, this worked successfully. I used a closed-circuit 1/8" phone jack from Radio shack (274-246) so that when nothing is plugged in, the normal AM circuit is complete from t2 to the volume knob. When something is plugged the connection back to t2 gets cut off.
:
:Right now it seems to work ok without resistors. Are you saying that the right and left channels from the ipod should each pass through a 50-100k resistor before being connected together? Will this reduce the volume?
:
:Thanks again, Ken H
:

Ken:
If it works OK right now without resistors, and you are happy, leave it alone and enjoy it. I am glad you took my advice about using a jack that would make for automatic operation.
Lewis

Ken,
I'm not familar with the IPOD low impedance headphone output circuit, but basic theory says don't connect 2 outputs together as you have. I would guess the output impedance is between 8 and 32 ohms, so a vacuum tube input will not load it down, even with a couple series resistors to avoid the two outputs driving each other, and protect the IPOD from eventual damage. Does your owners manual mention shorting of the outputs or using the wrong headphone. Most newer low power audio integrated circuits are short circuit protected at the output, but an ounce of prevention is worth a pound of cure. I think Mr. Murphy covered it quite well, "if something can happen it will"

marv

:Well, this worked successfully. I used a closed-circuit 1/8" phone jack from Radio shack (274-246) so that when nothing is plugged in, the normal AM circuit is complete from t2 to the volume knob. When something is plugged the connection back to t2 gets cut off.
:
:Right now it seems to work ok without resistors. Are you saying that the right and left channels from the ipod should each pass through a 50-100k resistor before being connected together? Will this reduce the volume?
:
:Thanks again, Ken H
:
:::I did this to my 1949 Mercury radio (in my 1951 Chevrolet). CDs sound nice. However I have found that mixing channels on solid state devices can cause distortion. You are better off mixing the two channels through 50-100K resistors (for the "hot" wires, not the ground wires....they can usually be tied together, since they always are with a headphone plug anyway).
:::
:::Another thing I did which is optional, of course, is put the RF filaments on the switch. In that case I was using a DPDT switch. Thrown one way the radio was connected to the amp, and the filaments of the RF tubes lit up. Thrown the other way they were disconnected, and the aux jack was connected. That saved me a little extra power, which, in a 1951 Chevrolet, is hard to come by. Now I have it running with a 90 ampere alternator regulated at 7.4 volts, so I have no problems with accessories. With the old 35 amp. generator, extra juice was little.
:::
:::T.
::
::Good idea, T. I got my experience when 45 RPM just came out, and RCA made a little record changer for 45 only. I adapted many a AA5 in some teenybopper bedroom to let her play the 45s (say Elvis) through her bedroom radio. My hormones hadn't kicked in yet, so the only reward I got was having all the girls smooching up to me while all the football players (who used to be the heroes) watched.
::Lewis

Ken,
As I recall, and unless newer techniques have arrived, modern IC audio power amps use a technique called BTL, "Bridge Tied Load", where each of the 2 leads (+ and -) are driven by a power stage, but out of phase similar to push/pull tube amps. Some consumer IC's offer this advantage selectable as either BTL or single ended drive on the same chip. The main advantage is the doubling of the power output in the BTL mode, but eliminates the DC blocking cap used in older solid state designs, and being co-located on the same silicon chip allows precision DC matching of the components as well. I've been away from this stuff several years and never studied it in detail anyway, but this technique, along with short circuit protection may be why you havn't destroyed your IPOD as yet.

marv

:Well, this worked successfully. I used a closed-circuit 1/8" phone jack from Radio shack (274-246) so that when nothing is plugged in, the normal AM circuit is complete from t2 to the volume knob. When something is plugged the connection back to t2 gets cut off.
:
:Right now it seems to work ok without resistors. Are you saying that the right and left channels from the ipod should each pass through a 50-100k resistor before being connected together? Will this reduce the volume?
:
:Thanks again, Ken H
:
:::I did this to my 1949 Mercury radio (in my 1951 Chevrolet). CDs sound nice. However I have found that mixing channels on solid state devices can cause distortion. You are better off mixing the two channels through 50-100K resistors (for the "hot" wires, not the ground wires....they can usually be tied together, since they always are with a headphone plug anyway).
:::
:::Another thing I did which is optional, of course, is put the RF filaments on the switch. In that case I was using a DPDT switch. Thrown one way the radio was connected to the amp, and the filaments of the RF tubes lit up. Thrown the other way they were disconnected, and the aux jack was connected. That saved me a little extra power, which, in a 1951 Chevrolet, is hard to come by. Now I have it running with a 90 ampere alternator regulated at 7.4 volts, so I have no problems with accessories. With the old 35 amp. generator, extra juice was little.
:::
:::T.
::
::Good idea, T. I got my experience when 45 RPM just came out, and RCA made a little record changer for 45 only. I adapted many a AA5 in some teenybopper bedroom to let her play the 45s (say Elvis) through her bedroom radio. My hormones hadn't kicked in yet, so the only reward I got was having all the girls smooching up to me while all the football players (who used to be the heroes) watched.
::Lewis