Converting a Tube AM radio to FM
There were many tube radios built from the early 1930's well into the 1960's that worked well, but received only AM broadcasts. The AM band has fewer and fewer stations, and are generally "Talk Radio". How easy would it be to convert one of these radios to FM?
Well, FM is fundamentally different than AM, so it's not just a matter of changing the frequency at which the radio operates. I have devised a device that you can plug into your working radio (replacing 1 or 2 tubes) to convert it to FM operation. It does not require modification to the radio itself, so will not affect the radio's value as an antique. These can be built by someone with an intermediate understanding of analog electronics. I have custom boards available, making it easy and neat to reproduce.
History of my FM conversion projects
FM Converter
FM_Converter_2025 Start here. This document describes the design and construction of the FM converter. For instructions for your specific radio, look at the "Radio-specific Instructions" below.
Youtube Video describing operation and installation.
How to assemble the circuit board CircuitBoard
Radio-specific instructions:
All-American 5
AC Radios
Car Radios
Component Selection and Circuit Board Availability:
This document describes where to get the boards and other components
This is a csv file to be opened with a spreadsheet and/or imported into digikey DigikeyPartnumbers
Historical Attempts:
First version, circa 2003 FM_Converter
The second version was quite complicated and I have not documented it, but I discuss it in the third version.
Third version, circa 2018 FM_Converter_2018
Fourth version, circa 2021. FM_converter_2021
Background Information:
Ap note on the Philips TDA7000 chip Philips_ap_note Here's the 7088 data sheet Data_sheet
There are better chips than the TDA7000 series. Check out the Skyworks (Silicon Labs) Si4800 series, used in the latest version:
Si4825 Si4825_Ap_Data Si4836 Si4836_Ap_Data
Data sheets for the PLL chips 4046 9046
Other's Inventions:
Lest I thought I was the only one trying to do this...
The FM5: an FM radio module for retrofitting tube radios from Radiofil in France RadioFil (I am told that this is obsolete and no longer being sold)
Another version from France FM-DW which is current and being made in large volumes.
An Italian Version Convertitore