R-390A Alignment Procedure

Resources used for the following included knowledge shared by Chuck Rippel, methods described in TM 11-856A and TM 11-5820-357-35, various reprints from National Radio Club , and articles from Hollow State News.

First Things First

Before starting with the alignments, the following should have already been completed:

Initial Setup

Set all front panel controls as follows:

1. Function Switch: MGC

2. Break-In Switch: irrelevant

3. Limiter: OFF

4. AGC Switch: FAST

5. Ant. Trim: 0 (important!)

6. Line Gain: CCW

7. Audio Response: WIDE

8. BFO Pitch: 0

9. Bandwidth KC: 4 KC

10. BFO Switch: OFF

11. Local Gain: CCW

12. Dial Lock: CCW

13. Zero Adjust: CCW

14. RF Gain: CW

Allow about 30 minutes warm-up before proceeding.

Connect a voltmeter between the Diode Load terminal and ground, reading negative DC voltage.

Mechanical Filter Alignment

Set the 455KC generator output level to cause the VTVM to read approximately 2.5V.

With the IF deck oriented so that the bandwidth control is towards you, make the following adjustments for a peak VTVM reading:

Set the bandwidth to 2KC

Align the top trimmers, C-568 located at 9 o'clock

Align the side trimmer , C-567 located at rear, top

Set the BW to 4KC

Align the top trimmer, C-569 located at 12 o'clock.

Align the side trimmer, C-566 located at rear, bottom.

Set the BW to 8KC

Align the top trimmer, C-570 located at 6 o'clock.

Align the side trimmer, C-565 located at front, top.

Set the BW to 16KC

Align the top trimmer, C-571 located at 3 o'clock

Align the side trimmer, C-564 located at front, bottom.

Fixed IF Alignment

Alignment of the fixed IF circuits may not be necessary unless components in the IF deck have been replaced (i.e. new capacitors). Early R-390A receivers had all IF cans tuned at 455 KC. Later R-390A receivers are stagger tuned from the factory. I prefer a stagger tuned IF because of the much wider and flatter frequency response. 

In the alignment listed below, set the signal generator output to give less than –7 volts at the diode load point, and peak the diode load voltage with each adjustment. Disconnect the signal cables from the RF deck to the IF deck (at J513 and J518). The signal generator output is fed into the IF deck through connector J513 (using cable normally connected to IF output). To peak T501 and T502 with stagger tuning, your signal generator output will have to be “much” larger at 443 and 467 KC; perhaps greater than 0.1 volts. Set the bandwidth to 16 KC, and increase the signal generator output until the diode load voltage is near –2 VDC. To peak T503, lower the signal generator output to give –3 VDC at the diode load using a 4KC filter.

Note: If you never use the 16 KC bandwidth, you can set the stagger frequencies narrower (say 463 and 447 KC), and you'll have a little more IF stage gain but not as flat a response in the 16 KC bandwidth position. Since most of your noise is before these stages, you may not see any real improvement in receiver sensitivity. Sometimes previous owners may have also clipped the "Q-spoiler" resistors inside T501, T502, and T503 to get higher IF gain. I undo this mod if I find it in any of my units.

Next, connect the VTVM to the AGC terminal and ground. Leave the signal generator set at 455 KC. Inject enough signal to bring the AGC voltage to –5 VDC. Adjust Z503 for maximum AGC voltage. Reconnect the signal cables from the RF deck to the IF deck.

Reconnect the VTVM to the diode load. Inject a 455 KC signal at 150 uV and adjust the IF gain potentiometer to give a diode load voltage of –7 volts DC. This setting can be optimized to find the “sweet spot” after a complete alignment by measuring the sensitivity and finding the IF gain setting that maximizes the signal to noise ratio.

Note: In my opinion, this setting of the IF gain potentiometer is MUCH too high. Go ahead and set it here for now so that you'll be able to get -7 volts DC for some of the following adjustments.  Just remember to lower it after you are done.  A more optimal setting is usually about half the range of the potentiometer.

2nd Variable IF Alignment

Connect the signal generator to the balanced antenna input jack as you would connect an antenna. Set the receiver and signal generator in turn to each frequency in the table below. Rock the KC back and forth to achieve maximum carrier level. This assures that the receiver and signal generator are on the same frequency. Adjust the signal generator output to give just less than –7 VDC on the meter.

Rock the MC change knob and make sure the diode load voltage returns to the same peak value. Repeat the above until you no longer make big changes to the trimmer caps, then stop.

Peak T207 at 1.9 MC.

1st Variable IF Alignment

Continue with the 1st IF alignment in a similar fashion, but start adjustments in the rear and move forward.

Repeat the above until you no longer make big changes to the trimmer caps, then stop.

Set the signal generator to above 8MC (about 10 MC), and peak T208 and T401 for maximum diode load voltage.

RF Alignment

Make sure the antenna trim is set at zero before proceeding.  The red dot should be in the 3 o'clock position if you are standing in front of the radio looking down at the RF deck.

The antenna balance should be adjusted first. This adjustment may be interactive with the movement of the first RF slug, so may required iterative adjustments if the slug position is adjusted significantly during the subsequent RF alignments.

Note: It is my opinion that this is an important step which is often overlooked. You're basically nulling out any signals that are not balanced. Some noise is of this type. This adjustment can make the receiver quieter in the presence of common-mode noise. 

Connect the signal generator to the junction of two 68 ohm resistors. Connect the free ends of the resistors to the balanced antenna inputs. Connect a VTVM to the diode load terminals, adjust the signal generator output to give about –7 volts diode load voltage, and minimize this voltage at he following frequencies: 

Be sure that a true balance is obtained, and not a minimum trimmer capacitance condition.  If you have two dips during 360 degree rotation, either dip should be giving a true balance condition.  If you only get one dip over the 360 degree rotation, some component value in the circuit has drifted too far away from its specified value and  the dip is occurring at minimum capacitance.

Set the receiver and signal generator in turn to each frequency in the table below. Rock the KC back and forth to achieve maximum carrier level. Adjust the signal generator output to give less than –7 VDC on the meter. You will be peaking the slugs at the low end of each band, and the trimmer caps at the high end. Peak the slugs at the lower frequency first. Then peak the caps. If you move the caps, go back through the cycle again until you don’t have to move the caps anymore. If you move the first slug by a significant amount, go back and check the antenna balance by repeating this adjustment. Then proceed to the next band.

Crystal Oscillator

You may use the CAL function for peaking the trimmer caps for maximum diode load voltage. But a better method is to use the line meter output and your ear with nothing but RF deck noise to peak each crystal for maximum audible noise and deflection of the line level meter. Peak the 17-24 MC trimmers at the lower bands (0-8 MC). After all are done, peak T401 (again) for maximum output at about 10 MC. T401 will peak differently on the higher and lower bands, so 10 MC is a compromise.

BFO Neutralization

Carrier Meter Zero Adjustment

With the ANT TRIM detuned and no signal injected, zero the carrier level meter (adjust potentiometer R523).

Calibration Oscillator Adjustment

Connect an antenna and tune to WWV at 5, 10, or 15 MC.  Zero-beat with WWV.  Switch the FUNCTION switch to CAL mode and zero-beat the CAL signal (without moving the KC knob) by adjusting the CAL ADJ capacitor through the rear panel access hole.  For improved adjustment, check the calibration against WWV at more than one frequency.

Stage Gain Check

To conduct the following measurements, connect a VTVM to measure diode load voltage.  For the stated signal generator output level, the diode load voltage should reach -7 volts.  This assumes that you have already aligned the IF deck and have adjusted the IF GAIN ADJ to give -7 volts at the diode load with 150 uV signal (455 KC) injected at J513.  This setting is NOT the optimal final setting for sensitivity, but is the basis for this test.  An alternative would be to measure the diode load voltage with 150 uV signal injected, and use that value for the tests listed below.

WARNING:  All connections to the test points are to be made through a 0.05 uF blocking capacitor.

^(a) Remove the 3 to 2 variable IF slug rack and tuned circuit Z216-3 before attempting this test.

Note:  An alternate means of conducting a similar series of tests is given on pages 95-100 in the R-390A Y2K manual.

Other Steps Not Covered

The following steps are not covered above, but are nonetheless essential.

Last edited: 04/26/2001