Converting an AM Tube Radio to FM
Updated June 2026
Many tube radios built from the early 1930s through the 1960s still work well but receive 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 developed a circuit that you can plug into your working radio (replacing 1 or 2 tubes) to convert it to FM operation. It does not require any 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 unpopulated circuit boards available, making it easy and neat to reproduce.
June 2026 update: A second (and probably last) iteration of the board is available.
History of my FM conversion projects
FM Converter (FMC) as seen in Winter 2025 (Vol 65, #4) edition of "The AWA Journal"
Start here: FM_Converter_2025 or FM_Converter_2025_V2 These documents describe the design and construction of the FM converter. The two documents are similar. I iterated the board (minor changes) in spring 2026, the V2 document reflects the newer version. For instructions for your specific radio, look at the "Radio-specific Instructions" below.
YouTube Video describing operation and installation.
Circuit Board Assembly Instructions:
Circuit Board <--V1 of board
Circuit Board V2 <-- V2 of board
Radio-Specific Instructions:
All-American 5 <-- The quintessential 5-tube AC-DC set with series tube heaters
AC Radios <-- Radios with large power transformers and parallel tube heaters
Car Radios <-- Tube car radios with negative ground
Component Selection and Circuit Board Availability:
Bill of Materials
This document describes where to get the bare boards and other components
This is a csv file to be opened with a spreadsheet and/or imported into DigiKey (you may need to disable your securiy software to download this file) DigiKey Part Numbers
For the dedicated: Turn your AM-SW radio into an AM-FM radio with small modifications to this converter AM-SW_Converter
This is what the board looks like (with Si4836 chip, and negative voltage generator. V2 board):
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
Fifth and final and best version, 2024-2026, is described above as the FMC.
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 Inventions:
I am certainly not the only person who has attempted 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