R.L. Drake

Drake Mods - General Mechanics

Authored by VE3EFJ


The "B" knobs are of two types. One is a set-screw type (as in number 2 and 3 above,) and the other is a slip-on type with the little metal spring like Collins uses. The set-screw type will work to replace either of the originals.

  • Sensitivity Check - all Drake 4 line
    All Drake receivers and transceiver should provide a noise peak as the preselector is passed across the tuning range, even on 10 meters. If your equipment does this with no antenna connected, you have all the sensitivity you can use. If it fails to provide a peak, alignment is immediately suspect. Generally, the calibrator should provide an S9 meter reading on 10 meters, progressively increasing as the band switch is rotated to 80 meters.

  • Front Panel
    The 4 line has spacers in the 4 corners of the front panel. Be care- ful when you remove the front panel. The thickness of the spacers seems to be 1/16" or so and they are, of course, black. They disappear as soon as they hit the ground.

  • Screws and fittings
    There are no metric fittings that I know of. Most of the machine screws are 4/40, the case cover screws are 6/32 and the chassis sheet metal screws are usually #4. The foot screws are 10/24.

  • Speakers
    All Drake equipment is standardized to 4 ohm speakers. This impedance is important. Use of 8 ohm speakers will produce considerably less audio output and is not recommended.

    On all the Drake C line and before, as in all audio power stages that have an output transformer, never crank up the audio gain with- out a speaker attached. Never connect an A/C volt meter across the primary. Transients generated in the output transformer, especially without a load, will create very high voltage spikes through the collapsing magnetic field. This is how output tubes arc, output transformers short and volt meter rectifiers get punctured.

  • Replacement Speakers (KD6VK)
    The speaker that I have used in several Collins speaker enclosures is a standard RS 5 x 7 replacement unit with 40-1261C as a part number. I have never used it with a Drake unit, but the sound should be similar if the speaker is any good. The key component is the spacing of the mounting holes and I believe that these are standard.

  • Power Supplies
    The Drake vaccuum tube transmitters and transceivers use the same AC/3 or AC/4 supply. When using alternate supplies such as the Heath HP-20 or HP-23 ensure that the low voltage 250 volt supply is indeed this level. Do not provide more than 265 on this power line.

  • Transmitter Meter PA Current Resistor
    When you buy your 'new' Drake, check the value of the cathode resistor in the final circuit. The value of this resistor will depend upon the model of transmitter or transceiver. I've seen a number of these cooked. Usually they go higher in value, causing a number of problems. With the resistor higher in value, the meter will read You'll end up setting the bias too low, causing poor transmitted au- dio.

    It would be wise to verify the meter calibration against the idling current. Using the T4C for example, it has its PA bias set for 70 ma and has a meter resistor of 3.3 ohms. Set to 70 ma, you should measure E=I*R, or .07*3.3 or .231 volts across this resistor. Measure across the resistor and NOT at the meter terminals.

    Similar problems with setting the proper idling current will be observed if the PA current meter needle is not resting at zero.

  • Intermittents
    Some intermittents may be difficult to find and somewhat hard to explain. Inspect the bottom of the chassis carefully and you will observe screws holding down terminal strips and circuit boards. All the screws that you can easily access should be backed off 1/2 turn and retightened.

    A TR3 suffered the above problems and was cured by the above approach. Most of this equipment is 20 years old or older. In the case of the TR3, it was 33 years. The obvious suspect is corrosion.

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