Fan Mod for Drake T4

REAR VIEW OF FAN INSTALLED

This modification adds a cooling fan as shown in the photo. This particular T4X received a 3-inch fan which required drilling four holes in the RF enclosure. We do not really need forced air cooling, all we want is better air flow than we get from natural convection. Therefore a smaller fan will also work well. A 2.5 inch fan can be mounted by using the holes already present in the RF cage.

SIDE VIEW OF FAN INSTALLED

The fan extends out from the cabinet but only for about an inch or so. Note the direction of airflow is into the cabinet. Airflow in the other direction would probably work as well, but this does the job well. There is no filtering of air. You can expect an above normal accumulation of dust from the fan and may need to clean the radio more frequently.

CLOSEUP OF THE THE FAN INSTALLED

SCREW HEAD AT THE INSIDE OF THE RF COVER

The mounting screws are installed with the heads inside the cover. This allows plenty of clearance to components under the cover.

If a three inch fan is used, the RF cover will need to be dr illed for the installation.

LOCATION OF THE FOUR HOLES IN THE COVER

The cover is steel. It will rust if the new holes are left unpainted.

CLOSEUP OF HOLE AFTER PAINTING

You can avoid the drilling and painting by using a 2.5 inch fan.

A 3 INCH FAN INSTALLED TO THE RF COVER

Power for the fan is obtained from the 12 vac filament supply. A single diode, half wave rectifier is used. It is filtered by a 100mfd/35vdc capacitor. A 51 ohm 2 watt resistor is used to reduce the voltage to the fan to about 11 vdc. The result is a whisper quiet fan and plenty of air movement. The actual value of the series resistor will vary from 10 ohms to 100 ohms depending on the current needs of the fan and your desire for airflow. Most fans of this type need current around 150ma. and voltage from 8 to 12 volts dc.

TOP VIEW OF CHASSIS SHOWING STAND-OFF LOCATIONS

Two teflon insulated stand-offs are used to support the additional components.

UNDERSIDE OF CHASSIS SHOWING ADDED COMPONENTS

There is plenty of room for the diode, resistor, and capacitor. The diode is connected from the filament supply to the final cage to one of the stand-offs. Cathode to the stand-off. The same stand-off is connected to the plus side of the capacitor. The grounded end of the capacitor is soldered to an existing ground lug in the radio. The resistor is mounted between the two stand-offs. Power for the fan is taken from the second stand-off. Teflon sleaving is used to protect the power lead. The return side of the fan motor is connected to a solder lug which is installed under one of the screws holding the RF enclosure.

The additional cooling should significantly improve tube life.

I AM OFFERING A KIT TO ADD A COOLING FAN

Included are:
1 - 12 vdc ball bearing fan (2.5 inch)with mounting hardware.
1 - 100mfd/35vdc capacitor
1 - Silicon Rectifier Diode
1 - 51 ohm 2 watt resistor
2 - Teflon insulated stand-offs and mounting screws
1 - Solder lug 1 - Complete instructions with schematic.
THE KITS ARE SOLD OUT AND NO LONGER AVAILABLE

The advantages of buying a kit are convenience and support.

All parts to do the conversion are included in the kit. With the exception of tools and solder, there is no need to scrounge for parts.

All kit purchases are guaranteed to result in a working modification. I will provide whatever support is needed to get your modification up and running.






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 Last updated Sep-2006

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