TABLE OF CONTENTS General Specifications 3 I General Description 5 II Installation Instructions 6 A. B. C. D. E. F. G. Unpacking Location Power Requirements Antenna Requirements Speaker Requirements Anti-VOX Muting III Control Functions A. B. c . 9 Front Rear Jacks Side Controls & Jacks IV Operation Preliminary Control Settings B. Single Sideband or Double Sideband Suppressed Carrier Reception c. C. W. Reception D . AM Reception E. RTTY Reception F . Adjusting Dial Calibration G .
27 VI Service Data A, B. C. D. Removing Top Cover Removing Bottom Cover Tube Replacement Troubleshooting 32 VII Alignment Instructions A. B. c . D. E. F. G. H. I. J. 27 27 27 27 50KC Oscillator Alignment 50KC I. F. Alignment Crystal Filter and Filter Match Transformer Alignment 5595 KC Oscillator Alignment Antenna RF, and Injection Circuit Alignment 100 KC Calibrator Alignment V.F.O.
GENERAL SPECIFICATIONS FREQUENCY COVERAGE: 3 . 5 - 4 . 0 MC , 7.0-7.5Mc, 1 4 . 0 - 1 4 . 5 , 21.0-21.5, and 28.5-29.0 MC with crystals supplied. Ten accessory crystal sockets are provided for coverage of any 10 additional 500 KC ranges between 1.5 and 30 MC with the exception of 5.0-6.0 M C . SELECTIVITY: Drake tunable passband filter provides: .4 KC at 6 DB down and 2.6 KC at 60 DB 1.2 KC at 6 DB down and 4.8 KC at 60 DB 2.4 KC at 6 DB down and 8.2 KC at 60 DB 4.
TUBES AND SEMICONDUCTORS: TUBE FUNCTION 12BZ6 12BA6 6HS6 6HS6 12BE6 12BA6 12BA6 2N3394 2 - 2N3394 6EH5 12BA6 12AX 7A 2N706 2N3858 2N3394 lN714 0B2 and lN483A 2 - lN3194 lN3194 lN270 and 2N3394 2 - lN483A lN483A lN483A 2 - lN270 R.F. amp. 100 KC calibrator 1st mixer Premixer 2nd mixer and xtal oscillator 50 KC I.F. 50 KC I.F. AVC amp./AVC det. Audio amp. Audio output Noise blanker amp. Noise blanker amp.
I GENERAL DESCRIPTION The DRAKE R-4A is an extremely versatile communication receiver designed to bring you every feature desirable for the ultimate in the reception of all modes of amateur communications. It provides a linear permeability-tuned solid state VFO with 1 KC readability, and premixed injection with crystal controlled high frequency oscillator for stability on all bands. A 100 KC crystal calibrator is built-in.
II INSTALLATION INSTRUCTIONS A. UNPACKING Carefully remove your R-4A from the packing carton and examine it closely for signs of shipping damage. Should any be apparent, notify the delivering carrier immediately, stating the full extent of the damage. Fill out and mail the enclosed warranty registration card so that your warranty will be effective. Save the packing material. You may need it later for reshipment or storage.
Antenna connection to the R-4A is provided at the jack on the rear of the chassis marked ANT. It is recommended that when the R-4A is used with a transmitter, the transmitting antenna be used; change-over being accomplished by an antenna relay. This function is provided internally in our model T-4 and T-4X Transmitters. E. SPEAKER REQUIREMENTS A good quality 4 ohm speaker should be connected to the jack on the rear of the chassis marked SPKR.
TR-4 R-4A AC-4/MS-4 o r R V - 4 y--- -- - ---I I This switch must b e in the TCVR position for transceiving and in t h e RCVR position for separate receiver use. lower C a b l e ~___.____ ~__Speaker Cable -Mute _~--- Line Receiver Antenna J Cable ____--_-_____.p FIG.
III CONTROL FUNCTIONS A. FRONT 1. MAIN TUNING - The MAIN TUNING knob of the R-4A determines the frequency on which you are receiving. The vernier skirt around this knob is calibrated in KC’s from 0 to 25. The main dial is calibrated in five KC divisions and has two scale S . Use the 0 to .500 scale for bands 7.000-7.500, 14.000-14.500, 21.000-21.500, etc.; use the .500 to 1.000 scale for bands 1.500-2.000, 3.500-4.000, 28.50029.000, etc.
by the transmitter. When in the N. B. position the noise blanker is energized, and when in the CAL position, the noise blanker is switched off and the calibrator is switched on. In these last two positions the muting function is the same as if the switch were in the EXT-MUTE position, so if external muting is not used, a shorted plug must be inserted in the Mute jack to obtain these functions. 6. SSB/CW-AM - This switch determines the detector which is used and the AVC mode.
For CW reception on the . 4 position the signal is tuned for most pleasing note with the frequency knob and is then peaked with the PASSBAND tuning knob. You can then tune other stations without changing the PASSBAND tuning knob setting. The audio frequency at maximum signal strength will be correct. B. 11. PHONE JACK - A PHONE JACK is provided on the front of the R-4A for private listening when desired. The jack automatically mutes the speaker output when headphones are plugged in.
C. SIDE CONTROLS & JACKS 1. S-METER ZERO - This control is the front-most adjustment on the right side of the R-4A chassis and is for the purpose of setting the S-meter needle to S-l under no signal conditions. 2. NOTCH ADJ. - The NOTCH ADJ. control located on the right side of the chassis is a balancing device whichdetermines the amount of attenuation obtained with the T-notch filter. This control needs to be set very rarely. For the proper adjustment, see operating instructions . 3.
IV OPERATION A. Preliminary Control Settinqs For all modes of operation set these controls as follows: FUNCTION BAND XTALS PRESELECTOR NOTCH R.F. Gain A.F. Gain B. - - On - - Set to desired amateur band (see “accessory frequency coverage” for information concerning coverage of other frequencies) - - NORM - - Peaked for maximum S meter reading on operating frequency - - Off - - Fully clockwise - - Comfortable level Single Sideband or Double Sideband Suppressed Carrier Reception 1. 2. 3.
Under crowded band conditions it will be advantageous to use the . 4 KC selectivity position and reposition the Passband knob for maximum S-Meter reading on a signal tuned in to the desired pitch. After the Passband control is adjusted thus, simply tune in a C W signal for maximum S-Meter reading and it will automatically be the correct pitch. It will sometimes be to your advantage to shift the passband of the receiver to the other side of the BFO frequency for better copy under crowded band conditions.
F. Adjustinq Dial Calibration The calibration of the main tuning dial on the R-4A may vary slightly from band to band due to the tolerance limits of the various crystals. Therefore, the main tuning dial index has been made adjustable by means of the small red knob to its right. To set the calibration on a given band, proceed as follows: 1. 2. 3. 4. 5. 6. G. Set Band Switch, Preselector, and Xtal switch to the desired band. Set Function switch to CAL. Set SSB/CW-AM switch to Slow AVC.
H. Operation of NOTCH control The notch control on the R-4A consists of a permeability-tuned T-notch filter in the 50 KC I. F. This filter is capable of producing a deep notch which can be tuned across the receiver’s I. F. for the elimination of interfering carriers in all modes of operation. In order to obtain optimum results using this control, it is first necessary to set the “notch adjust” control located on the side of the chassis as de scribed here. 1.
I. Accessory Frequency Coverage In addition to reception on 80, 40, 20, 15, and the 28.5 - 29.0 portion of 10 meters, the R-4A can be programed to receive any ten 500 KC-wide ranges between 1.5 and 30.0 mc (excluding 5.0 to 6 .O mc) by inserting the appropriate crystal in one of the ten accessory crystal sockets. These sockets face out the rear of the unit on the left side of the chassis. In order to determine the correct crystal frequency, simply add 11.
T h e f o l l o w ing table shows the correct crystal frequency, and Band s e t t i n g f o r r a n g e s b e t w e e n 1 . 5 a n d 3 0 m c ( e x c l u d i n g 5 .0 - 6.0 mc) NOTE that if you intend to transceive with the R-4A, the crystal chart in the T4/T4X b o o k s h o u l d b e f o l l o w e d i n s t e a d . When receiving ranges starting with an even megacycle, the 0.000 to . 500 range on the main tuning dial may be used and when receiving ranges starting with a half megacycle, use the ,500 to 1.
J. Fixed Frequency Operation The R-4A can be locked to a specific frequency by plugging the appropriate crystal in the crystal lock socket, located on the left side of the chassis, and positioning the XTAL/VFO switch to the XTAL position. When the switch is so positioned, the R-4A VFO and crystal oscillator system will no longer control the frequency. Crystals for this application should be of the parallel resonant fundamental variety with HC-6/U holders.
V THEORY OF OPERATION A. R.F. Amplifier A signal entering the antenna is applied to the grid of the low noise 12BZ6 R. F. amplifier tube (Vl) through the tuned circuit formed by the coil Tl and capacitors C21 through C31. Here it is amplified and the output is tuned by the circuit formed by coil T2 and capacitors Cl through C11. The signal is then applied to the grid of the 6HS6 first mixer (V2). B.
c. Second Converter The 5645 KC output of V2 is applied to the grid of the 12BE6 second converter (V3) through a crystal filter. This gives excellent cross modulation and overload characteristics by providing selectivity before the gain producing stages. The cathode, control grid and screen grid are connected in a Pierce oscillator configuration controlled by a 5595 KC crystal.
FREQUENCY -8 KILOCYCLES -4 -6 BFO 0 -2 4 2 6 NOTE‘ PASSBANDS ARE CONTINUOUSLY MOVABLE ABOVE 20 AND BELOW EIFO, FREQUENCY. 30 cn ii 3 W 0 40 50 60 FIGURE X 6 - SELECTIVITY CURVES KILOCYCLES -2 -I (6 FO) 0 I 2 3 4 5 6 \ \ \ 6 0 FIGURE # 7-EFFECT OF NOTCH ON 2.
F, Audio Output Audio signal from the AF GAIN potentiometer is applied to the grid of the 6EH5 audio output tube V-7 through two stages of AF amplifiers consisting of Q7 and Q8 and associated circuits. The audio output from this tube is then applied to the speaker or phones through audio output transformer T16. The ANTI-VOX jack is connected directly to the plate of V7 through C122. G AVC System The 2N3394 AVC amplifier(Q-4) is biased past cut-off to provide AVC delay. When sufficient R. F.
The S-Meter sensitivity control R-40 varies the sensitivity of the meter for calibration purposes by varying the resistance in series with it. I. Noise Blanker The noise blanker in the R-4A attenuates a received noise pulse by shunting to ground the output of V-4 during the time interval of the pulse. In other words, the receiver is turned off during the pulse. The 50 KC I. F. output of the second converter V3 is fed into the grid of the 12BA6 Noise Blanker IF amplifier V9.
The negative bias supply uses a IN3194 diode to provide -60 volts to the AVC system for minimum bias, muting, and control of RF Gain. An OB2 voltage regulator VII is incorporated to provide 108 volts regulated for operation of the xtal calibrator. A IN714 zener diode, in conjunction with V11 provides 10 volts regulated for the VFO and H .F. oscillator. The power transformer has a dual primary. As supplied, it is connected in parallel for 120 volt operation.
VI SERVICE DATA We will check and factory align your R-4A for a nominal fee of $10 .OO plus transportation charges if the set has not been tampered with. If repairs are necessary, an additional charge will be made. Units that have been tampered with or misaligned, will be repaired on a time and material basis only. A. Removinq Top Cover 1. 2. B. Removinq Bottom Cover 1. 2. c. Remove the three top screws on each side of the R-4A.
Figure #9 VOLTAGE CHART Number Type 1 2 3 4 5 6 7 Vl 12BZ6 -1.1 1.66 0 12.6* 140 129 0 v2 6HS6 0 0 6.3* 12.6* 140 80 2.8 v3 12BE6 -11.5 2.7 12.6* 0 140 132 0 v4 12BA6 -1.1 0 0 12.6* 136 93 2 v5 12BA6 -1.2 0 12.6* 0 110 80 0 v7 6EH5 2.9 0 12.6* 6.3* 0 91 140 V8 6HS6 -.8 0 0 6.3* 145 120 2.2 v9 12BA6 -1.29 0 12.6* 0 128 110 0 Vl0 12AX7A 70 -* 5 0 0 12.6* 148 0 Vll OB2 110 N.C. N.C. N.C. 110 N.C. .
Figure #l0 RESISTANCE CHART - Number Type 3 4 5 6 7 8 9 20K* Fil - Vl 12BZ6 4.4M 0 Fil 6K 6.5K 0 v2 6HS6 2.2M Fil Fil 6.5K 228K 2.2K v3 12BE6 Fil 0 6.5K 6.5K 0 v4 12BA6 4.2M 0 Fil 6.5K 9K 330 V5 12BA6 3.7M Fil 0 10K 12K 0 v7 6EH5 100 Fil Fil 500K 16.1K 7.2K V8 6HS6 350K 0 Fil 4.7K 25K 500 v9 12BA6 2.6M Fil 0 6.5K 8.3K 0 VlO 12AX7. A 158K 0 0 Fil 4.5K 3.
VII ALIGNMENT INSTRUCTIONS Alignment of the R-4A will require the following equipment. 1. A reasonably stable signal generator having a frequency range from 1.5 to 30.0 mc and variable output level. An 11 megohm vacuum tube volt meter (VTVM) 2. A 12.6 mc series resonant crystal. A WWV crystal for the WWV frequency most reliable in your area ( see ” accessory frequency coverage”) An alignment load consisting of a .005 mfd disk ceramic capacitor in series with a 1000 ohm l/2 watt composition resistor.
C. Crystal Filter and Filter Match Transformer Aliqnment 1. 2. 3. 4. 5. 6. 7. 8. 9. D. Attach signal generator to pin #l of V2 and set generator frequency to 5645 KC. Set level so that an S-Meter reading of approximately S-9 is obtained. Set Passband selector switch to 2.4 KC and set Passband knob until it points horizontally to the left. Adjust signal generator frequency for peak S-Meter reading. A high pitched audio tone should be audible from the speaker.
E. Antenna, RF, and Injection Circuit Aliqnment 1. Turn off receiver and temporarily connect a 10K resistor from the side rotor contact of S 5 C to ground, and from the corresponding contact of S5D to the nearby terminal strip terminal to which the red and white striped B+ wire is attached. S5C and S5D are the third and fourth bandswitch waffers as viewed from the front of the receiver. You will note that each of these switches have two rotor contacts . The ones in question are the most easily accessible.
100 KC Calibrator Alignment F. 1. Attach the antenna to the R-4A and tune in WWV at the frequency most reliable in your area. For crystal selection see the chart on page 18. 2. Set the Function switch to CAL. (A shorted plug must be inserted in the Mute jack). Adjust the calibrator adjust trimmer (C119) for zero beat with the unmodulated WWV carrier.
3. 4. 5. band tuning knob should be pointing horizontally to the left as viewed from the front. If it is not, loosen the knob set screw and reposition the knob. Tune in a crystal calibrator signal at 3.8 mc for zero beat. Set the Passband selector lever to .4 and set the Passband tuning knob to the center of the shortest line. Attach a VTVM to the AVC test point (TP-2) and adjust the four slugs on the rear of the passband tuner for maximum AVC voltage.
