This page only covers how to align an AM radio, which is the easiest to align and requires only basic test equipment. FM radios are much more complicated and require highly specialized equipment to align.
Getting Started First of all, alignment should only be performed on an AM radio that has been recapped and is *working * working*! *! It is never a troubleshooting technique and will not correct problems caused by shorted paper capacitors, faults in the power supply, OTR resistors, &c! Alignment be performed if components or wiring in the RF and converter sections were replaced, or to improve the reception of a fully-restored radio that is to be used for daily listening. Although I have heard some people people say to "alignment should only be performed by 'experienced' repairmen," the only way to get such "experience" is by actually doing it. Alignment can be practiced on a simple 5-tube AC/DC receiver before attempting to align more elaborate models with RF stages. The principles behind alignment is simple. The IF transformers transformers are all adjusted for peak response at the radio's radio's designed intermediate intermediate frequency, often 455 kcps. kcps. Then the tuning capacitor in the RF section is adjusted so that the dial reads correctly. Finally, the oscillator of the converter is set to produce a frequency that the difference (or less commonly, sum) of the intermediate frequency and the radio frequency to which the radio is tuned. tuned. If the radio employs employs an RF stage, there there will also be an antenna matching circuit which is adjusted for peak response too. Before attempting alignment, be sure you have all necessary tools and equipment. AM alignment requires the following test equipment: a voltmeter to use as an output meter, a modulated signal generator (described on the Equipment page), and an isolation transformer for transformerless radios. radios. If you plan to get serious in restoring restoring AM radios, I recommend an oscilloscope as well. You will also need need a set of alignment tools—I recommend AES's "CB Alignment Tool Kit" Part #S-T18-530, as it will contain tools for all radio types, from large "slot-type" tools for early radios to hexagonal types for later models. models. If possible, get the the service literature for your radio too, as it will contain any special procedures that are to be followed. A frequency counter can also be handy if your signal generator does not have a digital display on it or if you have reason to doubt the calibration accuracy of your signal generator.
Oscilloscope or Voltmeter? Some high-end antique AM radios with RF stages, like the RCA 2-X-61 for instance, will list "cathode ray alignment" in their service guide, and give connection information for an oscilloscope oscilloscope on their schematic. Usually they instruct to connect the oscilloscope to the AVC line; the oscilloscope servicing as the output indicator indicator during the alignment procedure instead of an AC voltmeter. If so, then it is strongly advised that you use this method over the "output meter alignment," as it will only be given if there is some particular advantages to it over the conventional AC voltmeter across the speaker coil. Usually it means alignment on that particular model is especially critical, for instance if narrowband IF transformers are used to achieve a sharp response or if "tight" (precision) L-C tracking across the full band is required. If this is used, the oscilloscope can be of any type, as wide bandwidth is not required. Be sure the coupling on its vertical amplifier is set to "DC" as this is you will only be
interested in the DC component of the AVC signal. The AVC voltage becomes more negative for stronger input signals, so it will be necessary to readjust the oscilloscope's vertical sensitivity to keep the trace visible as the stages are aligned. Using this method also gives a better indication of potential overloading, as you can visually see the radio attempting to cut gain on strong signals.
Alignment Example I recently aligned my Zenith L622 clock-radio to serve as a good illustration of the alignment procedure start to finish. Note that this is to serve as a general guide, as the service literature will give any special instructions that must be followed. The Zenith L622 uses chassis #6L03 with tube lineup 6BJ6, 12BE6, 6BJ6, 12AT6, 50C5, 35W4. Although this is a six-tube superheterodyne (uses a RF amplifier), the IF transformers are of sufficient bandwidth that alignment is not as critical as it on models like the RCA 2-X-61. Being as this is a transformerless model, an isolation transformer must be used. The one I used is part of my dim-bulb tester, which is hidden underneath the table.
Procedure The picture above shows the Zenith 6L03 chassis, along with the required alignment tools. The following procedure is given for it in its service manual: Operation
1
Connect Oscillator to:
Converter Grid
0.5 µF
2
3
Set Dummy Input Signal Dial Antenna Frequency At:
455 kcps
-One Turn Loop Coupled Loosely to Wave Magnet [Loop Antenna]
Trimmers
Adjust 600 Primary & kcps Secondary Slugs
1600 kcps
--
--
For I.F. Alignment
Oscillator
Set Oscillator to Dial Scale
Detector
Detector Alignment
Antenna
Align Antenna Stage
1400 kcps 4
Purpose
Preliminary Setup This picture shows all the necessary equipment. This includes the following: service manual from Nostalgia Air , signal generator (Smart-Kit 303), digital multimeter (Simpson 467), alligator clips, and connection cables. I am also using an HP 5315A
frequency counter, which is behind the DMM. Notice the cables and adapters I am using. The output of the signal generator is taken through an RG-58 coaxial cable to a pair of binding posts to which the alligator leads can be connected. Although it doesn't matter much for low frequencies like the AM broadcast band, 50Ω coax like RG-58 should be used for as its impedance matches that of standard signal generators. I am also using a binding-post-to-BNC connector so that I could quickly connect and disconnect my frequency counter, but this is not required. The multimeter is set to AC volts and connected across the speaker. The alligator clips are connected through a capacitor (in this case ½ µF, used to prevent the tube's bias voltages from passing into the signal generator) to the grid of the pentagrid converter tube. Wait, which of the tube's grids? Connect to the third grid, which carries the RF signal, not the first or local oscillator grid. This is pin 7 on the 12BE6 and is marked with an (A) on the schematic. The signal generator is connected to the clips. Now turn the radio on and allow it to warm up for a few minutes.
Adjusting IF Transformers There are two main styles of IF transformers. PreWWII models generally used ones with air-variable trimmer capacitors, which were accessed from the top for both primary and secondary, and fixed inductors. Post-WWII models used variable-core inductors and fixed silver-mica capacitors built into the base. Generally on postwar types, the core for the primary is accessed from the top and the secondary from the bottom. The IF transformers in this Zenith radio happened to be bizarre exceptions to those aforementioned standards. Being made in 1953, it uses the postwar "style," but with no hole on the bottom, just one at the top! Huh, what was going on here?! Was only one side of the IF transformer tuned? No, the schematic clearly shows both primary and secondary are tuned. Then I noticed an unusual illustration in the service manual, shown to the left. I wish I had an endoscope probe so I could have gotten an "inside" view of these strange things! The slug for the upper winding is hollow and has a slightly wider cross section than the lower one. Thus the lower one is accessed by slipping a slightly narrower alignment tool down through the upper slug all the way to the bottom of the can! To adjust the top one, a slightly wider tool is needed. This is an example of why I recommend getting a *good* set of alignment tools like the kind listed above. On coils like these, the tools must have tips exactly the correct size (to within a fraction of a mm) to turn the slugs.
Now set your signal generator to 455.0 kcps or whatever your radio's intermediate frequency is (this will be given in the service guide). Increase the output of the signal generator until you hear a squeal in the speaker. Keep the output of the signal generator low —just enough to get a good indication on the voltmeter. Adjust the IF transformers for maximum response. The usual recommendation is to start at the back and work your way to the front: that is, to start with the secondary of the last IF transformer, then peak its primary, and so on until you get to the primary of the first IF transformer. And then you repeat this procedure until no further improvement in signal level can be obtained. (Repetitions are sometimes needed because high-gain tuned amplifier stages may interact with one another.) If the radio is already in fair alignment this process will go quickly, as little adjustment will be required on the transformers. However, if the radio is badly out of alignment, as will be the case if some dummy randomly "fiddled" with them in the past, it will be necessary to reduce the signal generator output several times to prevent overloading as the system gradually nears alignment.
Adjusting RF Section Turn off the radio and disconnect the alligator clips that were connected to the converter section, as the IF stages are now aligned. The capacitor that was used is also no longer needed, so it can be put aside. Now it is time to get the RF section into alignment. This step will vary somewhat depending on the radio model. For radios with loop antennæ, the signal generator will likely be connected to a one or two turn coil of 22gauge wire loosely coupled to the radio's loop. "Coupled loosely" means to have the coil in the same orientation as the loop antenna and held slightly above it. For radios with external antenna inputs, the signal generator will be connected between that input and the metal chassis. For this step, the large flat-head alignment tool will be used to adjust the mica trimmer capacitors on the tuning capacitor. The trimmers for my radio are shown to the left. As described in the service guide, the one nearest the shaft is the adjustment for the oscillator, the middle one is for the "detector" (tunes the third grid of the pentagrid converter to the RF signal from the RF amplifier), and the far one is for tuning the antenna matching circuit. Radios without an RF amplifier will just have two trimmers to adjust. Be aware that these mica trimmer capacitors work by principle of "compression," the amount of force applied to them determines their capacity. So try not to push down upon the screw with the blade of your alignment tool when adjusting them, as this will cause the adjustment to change the moment you let off of it. You just want to move the screw of the trimmer inwards or outwards, no force should be applied.
Once you have your signal generator coupled properly to your radios RF section, turn the radio back on and allow it to warm up. Set the signal generator and the radio's dial to 1.600 Mcps, near the far end of the MW broadcast band. There should be a mark of some sort here if the dial scale is not attached to the chassis. Both accuracy and precision are crucial in adjusting these stages. If the accuracy of your signal generator is unknown and you don't have a quartz-referenced frequency counter to use as a reference, try using an off-air station for these steps, as the FCC requires AM stations to keep to their assigned frequency to within extremely narrow limits. Adjust the oscillator trimmer for peak response. Depending on the sharpness of your radio's response, you may have to "hunt" a bit until you pick up the squeal of the signal generator. There, now the oscillator should track with the dial setting. Now you want to peak the input side of the converter. This may be done at a different frequency than the oscillator tracking adjustment, like 1.400 Mcps in this case. A mark is provided on this radio so that the dial can to accurately tuned to this. Remember to keep the output of the signal generator low, just as in the IF alignment! For tube radios with RF stages, you may have to get inventive here, for they are often so extremely sensitive that they are overloaded even with the signal generator output turned down as low as it will possibly go. You will likely know if the level is too high, as the squeal from the speaker will be a blasting roar with the volume turned up! I have found that this can often be the case with the SK-303 signal generator, as it was designed for more modern AM radios that are much less sensitive than high-end tube radios. Like for this particular Zenith radio, I turned the signal generator's output down low, set the one-turn coil down under my table, and rotated it until it was at a right angle to the loop antenna. (This puts the laws of electromagnetics on my side, as it blocks the magnetic component of the field of the antenna that holds most of the power radiated, and allows only a portion of the weaker electric component to pass through.) Once I aligned an RCA 2-X-61 that I had to get really creative with. Once its RF section was nearing alignment, I found I had to connect the signal generator to a short piece (~30 cm) of wire and set it way, way off in a room on the opposite side of my house to obtain a sufficiently low output! Such extreme measures are unlikely to be required if you are aligning a simple 5-tube set.
Final Steps Lastly, you align the antenna matching section for peak response in the case of sets with RF stages. For elaborate AM or shortwave radios, there may be some addition steps that are performed, such as L/C tracking adjustments done at some low frequency like 600 kcps, but these will be easy and straightforward. Just as with the IF alignment, it may be necessary to repeat these steps for RF alignment a time or two in case there is any interaction between the circuits. Congratulations, your AM radio is now in proper alignment!
