AM and FM Alignment

What is Alignment?

Alignment is the process of adjusting the IF and RF circuits for best reception (sensitivity, selectivity and absence of whistles) and accurate indication of the frequency/wavelength on the tuning scale. The set will have been properly aligned when it was manufactured but could require realignment either due to component ageing and drift or because somebody ("The Phantom") has been fiddling with the adjustments previously.

You could compare it to tuning an engine - it will probably still run if it is off-tune, but not as well. And if it is a long way out of tune it probably won't run at all. Unlike an engine though, no damage can be caused by having a radio out of alignment, it just won't work quite as well as it could.

To do the job properly you need an RF signal generator, some means of indicating the output level, appropriate tools for adjusting the adjustments, and some patience! It is not too difficult providing you follow the procedure in the service sheet carefully - unless you run into a jammed or broken adjustment.

Before reading this section you will may it helpful to read the RF and IF stages page, so that you understand how the circuits work and can get a better feel for what we are trying to achieve.

Who is "The Phantom"?

"The Phantom" or "The Phantom Dabbler" is the person or persons unknown who had a go at fixing the set before you. What separates the Phantom from other repairers is that the Phantom invariably makes the situation worse.

He is the person who messed up the alignment and broke the cores in the IF transformers in the process. He is the person who attached several components in seemingly random positions underneath the chassis. He is the person who disconnected something then reconnected it wrongly. You get the general idea!

I first saw him mentioned in a book by Les Lawry-Johns published in the 1970s, but I am sure his name has been known to radio engineers long before then.

Deciding if AM Realignment is Necessary

The usual indications that the set requires realignment on MW and LW are poor reception and interference. The alignment will not normally vary greatly on its own, so if there is no sign that it has been disturbed in the past you should look for other causes of the problem first. In particular check the AGC and IF decoupling capacitors and resistors.

Replacing valves can affect the alignment slightly, but this is normally insufficient to give poor reception unless the replacements are not direct equivalents. If the IF transformers and RF trimmers appear to have been disturbed previously and the performance is below par, it is worth checking the alignment. I strongly suggest that you obtain a copy of the service sheet for the set before attempting any realignment.

Unless you have a suitable signal generator, you really should not disturb any adjustments. Never fiddle randomly with the adjustments, as one can do a great deal of damage to a perfectly aligned set by the overzealous use of a trimtool. I have included suggestions for adjusting the alignment without a signal generator, but these will probably only be useful if the alignment is not too far out before you start.

AM IF Alignment

I will use the Philips B2G81U circuit (discussed on the IF and RF Stages page) again for this discussion. The IF circuits must be aligned before the RF circuits.

Switch the set to MW, and set the tuning to a point near the centre of the scale where there is no station. Set the volume to near maximum and connect an output level meter (such as an analogue test meter on the lowest AC voltage range or the Audio Level Indicator on this website) to the speaker terminals.

If you wish to disconnect the speaker (because of the noise), replace it with a 3R3 wirewound resistor. Alternatively, connect an oscilloscope across the volume control.

Connect the RF output of a signal generator to the control grid of the mixer-oscillator valve (the junction of C4 and L1 in this case) via a 0.01uF capacitor. Connect the ground of the signal generator to the receiver chassis via another similar capacitor. Select a low output level, and switch the internal modulation on.

A suggestion from Leon Crampin:

Radios such as the Bush DAC90A need to have the generator connected to the UF41 grid during alignment. This can be a nuisance, as all other adjustments can be done in situ. Strip a piece of 7/0.2 flex back about 12mm and remove all but 2 strands. Put these into the grid pin socket in the valveholder, then feed the free end through the spigot hole and out under the chassis to connect to the generator. Replace valve.

Now switch the radio on and allow it a few minutes to warm up. Vary the signal generator frequency around the expected IF (normally 465KHz but check the service sheet) until the peak level is indicated on the output meter. If the IF does not need adjustment there should be a clearly defined peak as the signal generator is tuned close to the IF frequency. If the peak is not clearly defined, the IF probably needs adjustment.

Carefully adjust the cores of the IF transformers for maximum reading on the meter. Start with the transformer closest to the detector (L7/L8) and work backwards. Reduce the RF level as necessary so that the output level meter reads about half of full scale (if the level is too high the AGC will mask the peaks). If the set has AM and FM bands, take care to only adjust the AM IF transformers.

Always use a proper tool for adjustments - NEVER USE A SCREWDRIVER! A screwdriver is not the correct shape for the slots - the blade increases in thickness which can cause it to crack the cores. Also the steel blade affects the tuning. The correct tool has a flat blade and is normally non-metallic. You may be able to make something by filing down a plastic knitting needle.

The transformer cores will have been sealed in place with paint or wax. Take great care when attempting to adjust them, as it is very easy to damage the core. If the core has not been disturbed previously and will not move easily, it is best to leave it alone.

If you do not have a signal generator and the set can receive some stations, albeit weakly, you could try carefully adjusting each IF transformer core in turn to see if any improvement can be made. This approach is most successful if only one or two adjustments have been disturbed; it is unlikely to help with a set where the alignment is a long way out. You should take care to note the original positions of the cores so that they can be reset if the adjustment does not have any effect.

An idea from Leon Crampin:-

Seal trimmers and cores with typewriter correction fluid (Tipex) - easy to apply and does not jam up.

Dealing With Jammed IF Cores

It is possible for a core to become jammed at a position away from the correct position, and attempts to free it usually result in further damage. Leon Crampin has the following suggestion:

Ferrite and iron dust cores were often locked with wax, or more recently, a Rocol compound designed for the job. Over the years, both of these harden to the point where the cores will break if adjustment is attempted. A good solution is to apply a little ear wax remover to the core and leave for 5 mins. This works like magic for both wax and the Rocol compound. I have just aligned a (very) multiband 1951 Pye in which all the cores were stuck and one previously broken. This method shifted all of them without damage.

In further email discussions, Leon mentioned that the product he used is "Earex", which is a mixture of three oils, and is designed to simply soften wax. There is an alternative type of product, "Otex" being one brand, that contains other ingredients to break down the wax. We haven't tried this one on ferrite cores yet. If anyone has, please let me know how it goes.

Gary Tempest added the following suggestion:-

My usual ploy is to remove the other core (count the number of turns) and then try taking the jammed core out from this side. The most common problem is broken slots, where the wrong trimming tool has been used, so this trick works well.

I have tried this technique a couple of times, and can confirm that it works!

If these suggestions fail, then the best hope of obtaining the correct tuning is to insert a second core. Depending on the position of the original core, the additional core should be either ferrite or brass (ferrite will increase the inductance and brass will decrease it). Try inserting the end of a piece of thin brass rod (such as a short piece of studding or a pin from an old 2A round-pin mains plug) to see if it makes the mis-tuning better or worse. If brass is wrong, a ferrite core salvaged from an old IF transformer should be right. Having established what is needed, fix it in place with some wax (scraped from an old wax-coated capacitor) melted with a soldering iron. Unfortunately the result can look rather messy and unprofessional.

This approach is only suitable for some types of IF cans. Other types may have a protruding brass adjuster attached to the ferrite core, but these types are less prone to becoming jammed.

Dealing With Loose IF Cores

Another good suggestion from Leon Crampin:

The other day I had a core that was too loose in its former. The remedy is easy; PTFE tape. You apply the right amount to make the core a smooth but snug fit in the threaded former. As well as its inherent non stick qualities, PTFE is a low loss material; just what's needed.

AM RF Alignment

Before attempting to align the RF and local oscillator circuits, check the performance of the set. Often realigning the IF is sufficient to resolve reception problems.

The usual indications that the RF circuits need realigning are inaccurate calibration or poor reception towards one end of the scale. If the calibration is out (stations are not at the correct point on the scale), check the pointer is correctly positioned and is moving in the correct direction. There will often be dots or marks at one end of the scale, and the pointer should coincide with these when the tuning is set to this extreme. Do not expect great precision in the calibration, particularly on cheaper sets.

RF and oscillator alignment methods vary with different sets, so it is definitely worth obtaining the service sheet rather than guessing. In the absence of any other information, we will align the MW band at 250 metres and 500 metres.

Transfer the signal generator leads to the aerial and earth sockets on the set, putting a 100pF capacitor in series with the aerial connection. If the set does not have these sockets, connect a loop of two or three turns of wire about 6" (150mm) in diameter to the signal generator and place it near the internal aerial. Switch the set to MW.

Tune the set to 250 metres and set the signal generator to 1200KHz (1.2MHz). Adjust the trimmer capacitors that are connected in parallel with the tuning capacitor (C3 and C13 in the Philips) for maximum output.

Now tune the set to 500 metres and set the signal generator to 600KHz. Adjust the cores of any inductors in the MW oscillator and RF circuits for maximum output. In the Philips, adjust L6. If the set has a ferrite rod aerial, adjust the position of the MW coil.

Repeat these adjustments a couple of times until no improvement can be made. Adjust the RF level from the signal generator as necessary to give a reasonable reading on the output level meter.

Alternatively, these adjustments could be carried out using two radio stations that transmit on frequencies near either end of the band. Virgin on 1215KHz is a good choice because it should appear at the point marked Light (247 Metres) on the MW scale. Similarly BBC Five Live on 633KHz should appear at the position marked Northern (433 Metres). I normally do it this way.

The easiest way to align the LW RF circuits is to tune the set to the position on the dial marked Light (1515 metres or 198KHz), and adjust any settings that are only operative on LW (none in the Philips) for the best reception of BBC Radio 4. Also, adjust the position of the LW coil on the ferrite rod.

Do not attempt to realign SW circuits without the service sheet. Always follow the instructions on the service sheet, and make sure the signal generator you are using is accurately calibrated.

VHF IF Alignment

If the VHF IF alignment needs adjustment, the set may give distorted reception and lack sensitivity. If the set has a tuning indicator, the best reception may not occur at maximum indication. Bear in mind however that valve VHF sets are not as sensitive as modern transistor designs, so you could only expect to receive stronger signals such as the BBC national programmes and your local stations.

For this discussion, we will use the Ekco C273 circuit again. Connect a voltmeter across the ratio discriminator capacitor (C28) to act as a level meter. Switch the set to VHF and disconnect the aerial. The meter should read less than 1V.

Set the signal generator to the expected IF (normally 10.7MHz) and switch the internal modulation OFF. Connect the signal generator between one of the aerial sockets and the chassis via 0.01uF capacitors as previously. Vary the signal generator frequency around the expected IF, and try to find a peak. If the IF adjustment is OK you will find one clearly defined peak.

If not, adjust the cores of the VHF IF transformers for maximum reading on the meter. Start with the transformer closest to the tuner (L6/L7) and work forward. The first IF transformer is normally in the VHF tuner unit. Adjust the RF level as necessary to keep the output meter reading at about 4V.

Before adjusting the final IF transformer, you need to establish which core is the secondary. With vertical cans it is often (but not always) the top adjustment. If you have the service sheet you can check this, otherwise try adjusting them both slightly. The primary adjustment should peak in the same way as the other IF transformers and can be adjusted as previously. If it is still not clear, you may have to carefully dismantle the transformer to check.

The setting of the final IF secondary affects the performance of the ratio discriminator circuit. The various service sheets describe different methods of doing this, some requiring specialised equipment. I normally ignore these, and use the method that is described here. It requires no specialised equipment and works fine. It is based on the method described in most Bush service sheets.

Connect two 100K 1% resistors in series, across C28. Note that the comparative accuracy of the resistors is more important than the absolute value - they can be 68K, 82K, 100K or 120K as long as they are both the same value and are both 1% components. Connect a micro-ammeter between the junction of these resistors and the junction of R10 and C24. With the signal generator connected as previously, adjust the core of the secondary of the final IF transformer for a reading of zero on the micro-ammeter. This will be between a positive and negative peak.

It is possible to align the VHF IF stages without a signal generator by tuning to a fairly strong transmission and carrying out the adjustments as described above. BBC Radio 3 is a good choice because it is generally quieter than the other stations, and therefore there is less modulation to confuse the results. Of course, this assumes that the set is receptive enough to receive something before you start. The most tricky part to do by ear is the ratio discriminator.

VHF RF Alignment

If the VHF RF alignment needs adjusting, the scale calibration will be incorrect (the stations will be in the wrong places). The calibration may vary slightly if the ECC85/UCC85 valve is changed.

There is normally some adjustment where the VHF tuner links to the main tuning drive mechanism. This should be adjusted to bring the stations back into line. If there is no obvious method of varying the calibration, you should obtain the service sheet. Random fiddling could easily make things worse.

Since the VHF band on most valve radios only extends to 100MHz it will not be possible to receive stations transmitting on the higher frequencies. However you may be able to bring in some of these (particularly Classic FM at around 101MHz), possibly at the expense of stations at the lower end of the band (BBC Radio 2 etc.) and tuning scale accuracy, by careful setting of the above mentioned adjustment.

The VHF aerial matching transformer (L1/L2) should be adjusted for best reception of a weak station around the centre of the dial. This adjustment often has little effect.

I must emphasis again that it is easy to ruin a perfectly good set by fiddling with the alignment, particularly if the cores become broken or jammed. This is particularly the case if you are attempting to align the set without the benefit of a signal generator. Unless you are certain that adjustment is necessary, and have the necessary equipment, leave well alone!

Further Reading

Good alignment is important in achieving the best from your set, and the subject cannot be fully covered on a single webpage. For more detailed information, the new book by Chas E. Miller entitled "The How and Why of Alignment" may be of interest. Full details are on the books and magazines page.

This website, including all text and images not otherwise credited, is copyright © 1997 - 2006 Paul Stenning.
No part of this website may be reproduced in any form without prior written permission from Paul Stenning.
All details are believed to be accurate, but no liability can be accepted for any errors.
The types of equipment discussed on this website may contain high voltages and/or operate at high temperatures.
Appropriate precautions must always be taken to minimise the risk of accidents.

Last updated 14th April 2006.