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FM Converter for vintage radios by David WINTER

Tune with the original dial, listen through the original tube amplifier !

DAB / DAB+ ready (using a DAB-to-FM transmitter).

Modules come either spare (as pictured) or as a splitable 4-module board.
Prices include worldwide registered shipping.
This electronic circuit uses devices which are sensitive to electrostatic discharges.
It is housed in an antistatic bag before shipping and packing.
It must be carefully installed by a qualified technician after having properly restored the radio.
Full installation details (easy) will be provided in PDF to all buyers.
If you are not a qualified technician who knows how to restore tube radios, you are installing and using at your own risks.

The FM-DW module converts most vintage tube radios (mains powered) to the 87.5-108MHz FM band.
Stations are tuned using the original dial, and the original tube amplifier is preserved.

DAB/DAB+ radios can only be heard using a DAB/DAB+ to FM transmitter, which avoids cut-outs on the radio to insert additional controls and a LCD screen.

Note: this module connects to the tuning (variable) capacitor of the radio.
AM bands can only be preserved by adding a custom switch design.

Main specs:

- FM 87.5-108MHz using radio's dial for tuning.
- Mono audio output using radio's tube amplifier for listening.
- No additional controls required, no external mods !
- Easy to install: three grounded holes + grounded bottom layer.
- Powered by heater circuit or a DC source.
- 2ft (60cm) external antenna is enough in most cases (can be housed in radio cabinet).
- Very compact: 3cm x 3.5cm !

Installation procedure:

Before all, make sure that your radio is accordingly restored and NOT connected to the mains (plug MUST be removed). The mains switch of your radio should be cleaned and not produce excessive arcing.

The FM module does not require the IF section, so you may disconnect the plate and screen circuits to avoid replacing capacitors which won't serve. The tubes of the IF section may be removed only in radios with parallel heaters. If the high voltage increases too much after disabling the IF section, a resistor should be added to the DC "pi" filter, depending on how it is wired (i.e: output tube plate(s) connected before or after the filter).

- The module's ground must be connected to the chassis first, especially with AC/DC sets. The three grounded holes, as well as the grounded bottom side allow a solid attachment to the chassis.

- The module's CV pad must be connected to the tuning capacitor, which must have a grounded body and NO contact faults with the rotary part. Nothing else must be connected to the tuning capacitor except a trimmer, which, when present, should be set to its maximum. For short wave radios which use low capacitance tuning capacitors, several sections can be connected in parallel to add more capacitance. In this case, make sure that the minimal value doesn't exceed 50pF or so. For portable radios which have a positive ground (i.e chassis connected to the +), the tuning capacitor's body must be insulated from the chassis and grounded.

- The AC/DC in pad can ONLY be directly connected to a grounded 6.3Vac heater winding with no center tap. If the heater winding has a grounded center tap, or if it outputs less than 6.3Vac, a voltage doubler is required. The type of doubler depends on the type of heater winding (see schematics below). AC/DC radios without a grounded heater winding (i.e heater connected in series) MUST use a sparate DC power supply of at least 6Vdc and not more than 16Vdc. Miniature circuits from quality cell phone chargers work very well as long as they deliver at least 6Vdc. Radios with a 2.5V heater circuit either need a small step-up transformer (2.5V to 6.3V), or a separate DC power supply.

- The Antenna pad can be directly connected to the radio's antenna plug after removing the original components wired to it except for AC/DC radios, which must have a 1M Ohms resistor between the antenna pin and the chassis, and a 10pF capacitor (approx.) between the antenna pin and the antenna plug.

- The Audio out pad should be connected to the radio's LF amplifier through a 27K resistor, with a 150K resistor between ground and the end of the 27K going to the LF amplifier. This will reduce output noise, and increase sound fidelity. For AC/DC sets, you may add a 0.01µF/630V capacitor between the Audio out pad and the 27K resistor.

- Verify your wiring and connect an antenna. Calibration can now be performed.

Old calibration procedure, only for modules shipped BEFORE Nov 7, 2021:

- Turn the radio on. It is not required to wait for the tubes to warm up.
- Set the tuning capacitor to its maximum value (fully closed) and press the calibration button once. Pressing it twice or more won't affect the procedure. Radio can even be turned off if required.
- Set the tuning capacitor to its minimum value (fully open) and press the calibration button once. Pressing it twice or more won't affect the procedure.

Verify that the FM band now covers the whole radio dial.
Repeat the calibration procedure if necessary.

New calibration procedure for modules shipped AFTER Nov 7, 2021:

This calibration consits in choosing where the FM band starts and ends on your dial.
During calibration, the button must always be pressed quickly (i.e: less than a second).
The FM-DW module ships reset, and will not tune until full calibration is performed.
- Turn your radio on. It is not required to wait for the tubes to warm up.
- Set the dial where the FM band should start (87.5 MHz) and press the calibration button once.
- Set the dial where the FM band should end (108 MHz) and press the calibraiton button once.

If you happen to press the calibration button by mistake or by accident, or if you get lost during this procedure, the module can be reset as follows:
- Power the FM-DW module OFF and wait for a few seconds.
- With the calibration button pressed, turn the FM-DW module ON. Release after a second.
- The FM-DW module is now reset and stays silent: you may power it OFF and calibrate again.

Verify that the FM band now covers the whole radio dial.
If a new calibration is necessary, reset the module before calibrating.