Convert DAC to add FM

[Ruairi]

Hi I'm looking for an electricity-certified repair person to modify and add FM to my DAC 90A, since the BBC on LW will cease in a few days.  Grateful for any suggestions. Ruairi C

[boater sam]

Hi,  
A DAC 90A is not perhaps the best set to convert to FM as its a live chassis with no transformer and has no low voltage supply to power the conversion.
It is possible, just not as easy as a set with an earthed chassis and transformer.
Do you have another set you could convert?

[Mike Watterson]

It would be easier to have a micro power LW or MW AM with a loop to couple to radio. Feed it from Satellite, FM radio or even DAB.

[ppppenguin]

This thread discusses adding Bluetooth to a DAC90A: https://golbornevintageradio.co.uk/forum...p?tid=9216 Seems like an easier proposition than making a safe FM conversion. Though it also mentions adding David Winter's FM module.

[boater sam]

The David Winter conversion will work but the question of a power source remains. Possibly using the output valve cathode bias may provide the necessary voltage but its contentious. 
Providing a mains fed transformer for the conversion and at the same time converting the poor pilot lamps to 6.3v fed from the same transformer would be the best solution.

Sam.

[bobhowe]

The David Winter conversion will work but the question of a power source remains. Possibly using the output valve cathode bias may provide the necessary voltage but its contentious. 
Providing a mains fed transformer for the conversion and at the same time converting the poor pilot lamps to 6.3v fed from the same transformer would be the best solution.

Sam.

Hi Sam you can fit an Auto transformer that Ed Dinning can make it will still be a live set but it has a 6.3v winding for the dial lamps and this can power the David Winter Module . Having this Auto transformer is a big bonus that you have bright dial lamps cooler running set and his conversion works superb i will ask David winter to post a topic about these excellent FM Modules kind regards Bob

[david winter]

The David Winter conversion will work but the question of a power source remains. Possibly using the output valve cathode bias may provide the necessary voltage but its contentious. 
Providing a mains fed transformer for the conversion and at the same time converting the poor pilot lamps to 6.3v fed from the same transformer would be the best solution.

Sam.

Powering the FM-DW module using the 6.3Vac heater circuit is the usual way to do. Of course this supposes that one side of the 6.3Vac winding be grounded. This won't work if for example the 6.3Vac is a part of an auto-transformer.
For AC/DC sets I always use a separate 12Vdc supply. You need under 100mA so those tiny Chinese PSUs will do. I also add a series resistor to drop the voltage down to 7Vdc or 8Vdc, which reduces the inherent noise of those switched PSUs.
In any case, never power the module from the cathode bias voltage.

[bobhowe]

It would be easier to have a micro power LW or MW AM with a loop to couple to radio. Feed it from Satellite, FM radio or even DAB.

Hi Mike David Winter is trying to reply to this thread please could you validate his new account kind regards Bob

[PerdioPal]

A small "wall wart" power supply with case removed will supply the power, and very cheap too. As to using the cathode bias for supply I can't see a problem if it is derived from a 5V1 Zener diode in series. That would give the output valve an easier life and still have the same current/voltage ratio for "auto bias" albeit with a lower standing current. We (well me) never use the full power of a radio anyway.