Re: Retro fit radio
Posted by HH56 On 2020/2/17 16:58:09
I am not sure I would hold my breath for something working off the control head only. I believe the person who did the radio in the video may be a poster here and if he sees your post may have lots of insight. If not, I will offer 
Because the control head on pre 41 radios connects via mechanical cables to work the on/off volume control and tuning capacitor in the power box and the modern radio on a board kits such as that Aurora used in the video still relies on some of the original radio controls and signals for its command and station select needs, I have not heard of any retro fit that can just use the head alone without having a control box from which to take the needed signals to feed to the modern boards.
I would think it certainly possible to have the mechanical controls work the shafts of a complete modern radio as far as on/off and volume but it would probably take some serious engineering to get the old head knob turn ratio to turn the modern tuning control exactly correct so the radio dial indicator in the head unit would align with the frequencies as shown on the dial in the modern radio. It could probably be done with a custom gear train such as used to match speedos to different transmissions. Just have not heard of anyone trying to do it.
One other issue is if it is a deluxe head, some of those with push buttons in the head unit most often controlled an electric motor in the power unit to turn the tuning capacitor to a specific spot when one of the buttons was pushed. On other models the buttons did control separate oscillators but still those modified the base tuning circuit electrically just as turning the knob or motor would mechanically. Believe the screws inside the knobs on the 22-23 series radio in the video used to set the stations move a tuning oscillator operated by the button which modifies the tuning capacitor. On later radios a cam is moved and setting the cam to a specific angle moves the tuner to a controlled spot to select a station. In either case the tuning signal is still used for changing stations in the board kits.
No idea if the buttons could be made to directly work a kit unit without having some kind of tuning signal. 55-6 radios did use electrically connected tabs which slid across a support under the buttons and was positioned at a particular station. When a button was pushed its tab supplied an electrical signal to the tuning mechanism which stopped when the position of the tab was sensed. If the modern radio could support direct input from the buttons similar to that operation then head buttons alone maybe could be made to work the circuitry. I would think there would need to be some serious shielding and some kind of interface to the push buttons and wiring so electrical noise in the rest of the car could not get fed back to the radio. Also, old mechanical switches frequently "bounce" when making a connection. The period of instability before a solid on or off connection is finally obtained from the button is insignificant on old circuitry but could cause damage to solid state components.
All in all, I would be surprised if there would be enough demand for anyone to spend time and money developing an interface to a radio that would work with just the heads. If you do not have buttons to contend with then it should be simple enough to make adapters for the shafts to be turned with the heads mechanical cable operation only -- provided you can find a gear kit to get the tuning ratios in the range of being correct.
For a modern radio, have you considered something like a Secret Audio setup. It would need a 12v inverter to power it off a 6v car but with one of those the original head would be a dummy for looks only or, if you have the entire original radio, that setup could be kept intact. The electronics for the Secret Audio could be hidden and radio operated by their remote control or you could mount their small head somewhere. The head could be in the glovebox or made to fold up and hide under the dash.
Because the control head on pre 41 radios connects via mechanical cables to work the on/off volume control and tuning capacitor in the power box and the modern radio on a board kits such as that Aurora used in the video still relies on some of the original radio controls and signals for its command and station select needs, I have not heard of any retro fit that can just use the head alone without having a control box from which to take the needed signals to feed to the modern boards.
I would think it certainly possible to have the mechanical controls work the shafts of a complete modern radio as far as on/off and volume but it would probably take some serious engineering to get the old head knob turn ratio to turn the modern tuning control exactly correct so the radio dial indicator in the head unit would align with the frequencies as shown on the dial in the modern radio. It could probably be done with a custom gear train such as used to match speedos to different transmissions. Just have not heard of anyone trying to do it.
One other issue is if it is a deluxe head, some of those with push buttons in the head unit most often controlled an electric motor in the power unit to turn the tuning capacitor to a specific spot when one of the buttons was pushed. On other models the buttons did control separate oscillators but still those modified the base tuning circuit electrically just as turning the knob or motor would mechanically. Believe the screws inside the knobs on the 22-23 series radio in the video used to set the stations move a tuning oscillator operated by the button which modifies the tuning capacitor. On later radios a cam is moved and setting the cam to a specific angle moves the tuner to a controlled spot to select a station. In either case the tuning signal is still used for changing stations in the board kits.
No idea if the buttons could be made to directly work a kit unit without having some kind of tuning signal. 55-6 radios did use electrically connected tabs which slid across a support under the buttons and was positioned at a particular station. When a button was pushed its tab supplied an electrical signal to the tuning mechanism which stopped when the position of the tab was sensed. If the modern radio could support direct input from the buttons similar to that operation then head buttons alone maybe could be made to work the circuitry. I would think there would need to be some serious shielding and some kind of interface to the push buttons and wiring so electrical noise in the rest of the car could not get fed back to the radio. Also, old mechanical switches frequently "bounce" when making a connection. The period of instability before a solid on or off connection is finally obtained from the button is insignificant on old circuitry but could cause damage to solid state components.
All in all, I would be surprised if there would be enough demand for anyone to spend time and money developing an interface to a radio that would work with just the heads. If you do not have buttons to contend with then it should be simple enough to make adapters for the shafts to be turned with the heads mechanical cable operation only -- provided you can find a gear kit to get the tuning ratios in the range of being correct.
For a modern radio, have you considered something like a Secret Audio setup. It would need a 12v inverter to power it off a 6v car but with one of those the original head would be a dummy for looks only or, if you have the entire original radio, that setup could be kept intact. The electronics for the Secret Audio could be hidden and radio operated by their remote control or you could mount their small head somewhere. The head could be in the glovebox or made to fold up and hide under the dash.
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