Known and used by hams the world over for 13 years, the old HRO now has a new successor - the HRO-7 - incorporating every one of its strong points and adding a number of modern refinements. To begin with, the HRO-7 is housed in a streamlined gray cabinet which will enable you to meet the XYL's former objections to bringing your rig into the main part of the house. The whole family can listen when you pick up a French OP talking about the latest UN news. Two new miniature tubes have been added to further stabilize the receiver. This will enable you to turn the rig off and on again with an absolute minimum of retuning. As you turn the RF gain control, there'll be no appreciable change in the pitch of code signals and the HRO-7 remains unaffected by normal fluctuations in the voltage sent in by the power company.
The HRO-7 Radio Receiver is a twelve tube high-frequency superhetrodyne for the reception of code and phone signals throughout its frequency range of 50 to 430 Kcs., and 480 to 35,000 Kcs. Long an outstanding and proved performer in Communication and Amateur services, this new series of HRO-7 Receivers features many new refinements emanating from the latest advances in receiver circuitry and design. A new automatic, adjustable threshold, double action noise limiter effectively reduces interference caused by external noise pulses. Two new miniature type tubes, a 6C4 high-frequency oscillator and an OA2 voltage regulator, are employed to give a high order of oscillator stability. The addition of an Accessory Connector Socket, Tone Control, plus other electrical and mechanical revisions give this new HRO greater flexibility and adaptability. A 6 position crystal filter, maximum bandspreading of the Amateur bands, and an excellent signal-to-noise ratio continue to make the HRO a dependable Receiver, capable of maintaining communications despite the most adverse conditions.
CIRCUIT: The circuit employed on all bands comprises two tuned stages of radio frequency amplification, a tuned first detector, a high-frequency oscillator employing a tube separate from the first detector tube, a first intermediate frequency amplifier stage employing a variable-selectivity crystal filter and a conventional second intermediate frequency amplifier stage both operating at 456 kilocycles, a combined second detector - automatic volume control stage, an automatic adjustable-threshold series valve noise limiter, a first audio amplifier stage, an audio output stage and a beat frequency oscillator coupled to the second detector to provide for C.W.reception. A voltage regulator tube is used to regulate the plate supply to the high frequency oscillator tube.
|First R.F. Amplifier||6K7|
|Second R.F. Amplifier||6K7|
|High Frequency Oscillator||6C4|
|First I.F. Amplifier||6K7|
|Second I.F. Amplifier||6K7|
|Diode Detector, A.V.C.||6H6|
|First A.F. Amplifier||6SJ7|
|Beat Frequency Oscillator||6J7|
TUNING SYSTEM: The frequency coverage of the HRO-7 is covered in nine bands as follows:
|COIL SET||GENERAL COVERAGE||BANDSPREAD|
|A||14.0 - 30 Mc.||27.0 - 30.0 Mc.|
|B||7.0 - 14.4 Mc.||14.0 - 14.4 Mc|
|C||3.5 - 7.3 Mc.||7.0 - 7.3 Mc.|
|D||1.7 - 4.0 Mc.||3.5 - 4.0 Mc.|
|E||900 - 2050 Kc.|
|F||480 - 960 Kc.|
|G||180 - 430 Kc.|
|H||100 - 200 Kc.|
|J||50 - 100 Kc.|
|AA||27.0 - 30.0 Mc.|
|AB||25 - 35 Mc.|
|AC||21.0 - 21.5 Mc.|
The micrometer type MAIN TUNING dial drives the four gang main tuning capacitor through a worm drive having a reduction rate of approximately 20 to 1. Backlash is eliminated by the use of a spring - loaded split worm wheel which assures positive drive in either direction at all times. This dial has an effective scale length of approximately twelve feet and is calibrated from zero to 500.
NOISE LIMITER: The new noise limiter in the HRO-7 is the automatic, adjustable-threshold, series valve type. This limiter is double acting - limiting noise on both positive and negative peaks and is equally effective on both C.W. and phone reception.
CRYSTAL FILTER: The crystal filter, located in the first intermediate frequency amplifier stage, is extremely flexible and of most efficient design. A six-position selectivity control and a crystal phasing control are front-panel mounted for adjustment of the crystal filter. Operation of the phasing control provides for easy suppression of interfering signals which may produce objectionable heterodynes.
SIGNAL STRENGTH METER: Signal input reading are indicated in "S" units from 1 to 9 in 5 db. steps and in db. above S-9 from 0 db. to 40 db. on the panel mounted signal strength meter.
AUDIO OUTPUT: Two audio output circuits are provided. Loud-speaker terminals in the form of a five prong socket are located at the rear.of the Receiver and a phone jack is mounted on the front panel. The loud-speaker must have an impedance of from 5000 to 7000 ohms to properly load the output tube.
697 Power Unit, 115 and 23 volt;
SPU-697, same as 697 but mounted on a 5 1/4" rack panel;
686S Power Unit, 6 volt battery operated vibrapack;
MCR Table Model 8" PM dynamic loudspeaker with matching transformer;
RFSH Loudspeaker, same as MCR but mounted on a 8 3/4" high rack panel;
NFM-07 Narrow Band F.M. Adaptor;
SPC Combination Unit, an installation consisting of a power unit, coil container and 8" PM dynamic loudspeaker mounted on a single rack panel 15 3/4" high.
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