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2026 FM Tuner Alignment Generators & Tools

ConradH

ConradH

Lunatic Member
Everything I've written in the past is old now. I just saw what SG-165s can go for and it's nutso. I'm hoping we can collect some information here for people wanting to learn about tuner alignment. What generators are available, what other tools and gadgets and what books and educational stuff to read.

One way or another you'll need a stereo FM generator. That can be the SG-165, Sound Technologies ST-1000A, Leader LSG-231, Heathkit IG-37 and 5237 and various more modern units like Kenwood and others, usually from overseas. The old standbys have gotten very expensive, IMO more than they're worth and they always need service and updating. The Kenwoods and other more modern ones can be half the price, but I don't know anything about them. Hopefully people will chime in. There may be other solutions that I'm equally ignorant of. Whatever you get, make sure you can get a service manual for it.

You'll have to DIY some things like dummy antennas, impedance matching transformers and filters to keep the MPX carrier signal out of the THD analyzer.

You'll positively need plastic alignment tools.

Even if you don't have one, download and read the SG-165 manual. It has a huge amount of general information.

In the old days I would have said don't bother trying to get a scope fast enough for the FM band, but today it's so easy I say, why not.

Anyway, if you have a thought to contribute, this is the place!

(Extra thought, I'm surprised nobody has cloned the SG-165 and sold cheap boards to make your own.)
old but good- Radio-Electronics October 1961 : Gernsback, Hugo : Free Download, Borrow, and Streaming : Internet Archive
 
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Many top-end FM tuners require alignment adjusted to minimize distortion and the SG-165 has too much audio distortion to be usable for this but it is good for most other units. If you have a quadrature detector with a detector coil that has one winding for tuning and another for minimizing distortion, you will not be able to tune for lowest distortion because the audio modulation has about 4% distortion.

For those of you rebuilding an SG-165, check the voltage at the source of TR-316. If it is low, you may be OK, but mine was at 6 volts (well within the MPF-102 spec) and that puts 18 volts across 400 ohms (counting R368). When I got mine, the output was clipped in the negative direction for the 400Hz output. The simple reason was R365 was a 1/2-watt resistor carrying 22.222 mA and dissipating 0.8666 watts. The 1/2 watt resistor had gone up to 2195 ohms. I put in a 1 watt resistor and it looked OK but was running too hot to touch, so I then added a 2 watt 390 ohm resistor and turned down the voltage balance on the power supply so I would get 12.1 volts on the positive output but 11.4 volts on the negative output. There is no reason to balance the power supply voltages - nothing depends on it.

I replaced the filter capacitors (input and output) in the power supply because the 15 volt rating on the 12 volt outputs means the reliability will be low, especially if the unit is turned on and the output voltage rises before the regulator has a chance to stabilize it. If I was going to be totally anal about it, I would change the rectifiers to fast recovery types as ordinary rectifiers tend to ring at 30 MHz and harmonics thereof and the third harmonic would be in-band for FM. A snubber capacitor may do the same thing, just less effectively.

I had to replace TR302 and TR316 because they were blown. I also added a 1.5 meg resistor to ground from the base of TR301 because I am not comfortable running transistors with a 15 volt Vceo with the base open when the resistor will bring it closer to the 30 volt Vcbo. I also replaced TR314 because it appeared to be shorted going by the diode voltage test on my DMM, but that was a mistake - it was actually seeing R358 and the removed transistor tested OK.

I can't complain about the SG-165 I got for $10 with these defects plus one channel of the audio meter was butchered - leads cut and not reconnected for some reason, but I never expect to use that function anyway. It was a piece of test equipment designed to a price to enable the average TV repair and stereo store to have AM - FM - FM MPX repair capability and it succeeded in that mission. I used PN3563 transistors for the oscillators, which are plastic versions of the SE-3002 transistors on the schematic and the 2N3563 transistors that were actually installed. The Vceo goes from the 12 volts of the SE-3002 to 15 volts on the PN3563 / 2N3563, critical in this circuit.

The unit is a royal pain to work on. It is built like a ship in a bottle and there is a delicate plastic shaft that has to be protected from breakage. If you fix the design faults, it is a good unit if you have limited space and must choose one unit for checkout of radio functionality.

I also have a Heathkit IG-37 and the previous (same design) iteration, the IG-112. These three units are fine for early tube tuners and were designed to give a stereo shop or TV repair shop the capability to fix their contemporary tuners. I wouldn't pay big bucks for any of them now.
 
Yes to everything about the SG-165! It's a royal PITA to work on. I was also a bit shocked by the size, having never seen one in the flesh before I got one. Many are missing the cables with the isolator/probe thingy, but the manual shows how to build it. Being a pain to work on, I never wanted to do it again, so I used well over-rated tantalum caps in some locations. The output control is a completely unobtanium 75-ohm L-pad that's prone to wearing out, but a low value carbon pot also works. I know about the high THD, but the interesting thing is I've never been able to improve an alignment by using a lower THD generator. No doubt it's a factor, but if all I had was the SG-165, I wouldn't agonize about it. There's a schematic or descriptor error in the power supply, maybe polarity, depending on the unit. A search should turn it up. Note that the output signal can be smaller than you can see on your scope, so don't assume it's not working.

My daily driver is a Leader LSG-231. There are several revisions and you can find every available manual on my site in a big zip file. It's a one trick pony so you should have another generator that covers the FM band.

The Heathkit IG-37 and similar are better than nothing but are certainly inferior to the SG-165. I actually think they have some kind of design flaw as the tuned sections that are supposed to be symmetrical end up with very different slug positions after calibration. Or, I just don't fully understand the thing.

There are several classic books on FM theory and tuner alignment. They tend to be expensive, if available at all. A search around Anna's Archive could be worthwhile.

Hint #1- If you're going to find time at the bench enjoyable, you should enjoy making cables for your test equipment. You should be able to correctly assemble BNC connectors. I use small RG-174 coax for most things. When doing FM alignment, it's important not to have stray signals getting into areas you don't want or expect them. It's also important that ground leads be as short as physically possible. Make up cables with just a tiny amount of the center conductor exposed, maybe with a tiny connector socket and a short ground clip. Solder a short stub of wire to injection points so you can plug your cable on.

Hint #2- FM alignment is done down in the noise. If your signals look nice and clean, they're too big and you're not getting precise peaking. Turn things down so you can just barely do what you have to do, but not larger.

Hint #3- Commercial stations will get into the unit and contaminate the alignment. That often results in tuning meters not agreeing with signal strength meters and with actual sound quality. Consumer receivers are not very well shielded. Sometimes it's better to do alignment during the day when you can more easily find quiet spots on the dial. When the procedure says to do something at a certain frequency, you may have to do it at a nearby quiet spot, changing the generator frequency as needed.
 
A few signal generator / FM multiplex options that I've owned. Most of these can be had for good prices if you wait since they are not in demand like common ones you mentioned above. I got the 8644B + 8904A combo for just a tiny bit more than the ST1000A's were going for. The HP and Fluke gear general has excellent service manuals available (unless you go too new - I think some of the compact HP RF gens toward the end or early Agilent stuff started to drop them)

A combination of an RF signal generator + HP 8904A synthesized signal generator to generate the MPX signals. Note, the 8904A has to have a serial number starting with 2948A or higher, and have option 001 to get the FM MPX generation option. The 8904A is a nice general purpose audio repair tool as well, it can even provide balanced output for other uses. Option 002 is nice, as it adds a second output which can be controlled independently of the first.

I used the 8904A with an 8644B RF generator but there are dozens of RF generators you can use. HP 8656b/8657a, 8644, fluke fluke 6070a/6080a and their derivatives, gigatronics rebranded versions of them, Marconi signal gens, etc. You can usually find the RF generators at hamfests, but the 8904A will likely have to be sourced online.

I downsized a bit and currently own a Rohde & Schwarz SML-01 with the SML-B5 option. The B5 option adds the FM MPX. It is sometimes found on the SML-02 and SML-03 as well, those are 2 and 3 GHz generators. These sometimes fly under the radar, but I think finding them with the B5 option is pretty rare in general. I think the most common failure on them is the LCD, but it can be replaced easily.

A nice bonus of the SML is that you can pair it up with a UPL and there is a whole FM stereo receiver test suite, I show an example here:
pac1085

Post in thread 'Rohde & Schwarz UPL Audio Analyzer & FM Performance Tests with SML Signal Generator'

Here are some results from the UPL / SML-01/B5 FM Tuner Performance tests. This was on my McIntosh MR74. It works well although I haven't serviced it myself yet. There was a sticker inside indicating it was last serviced by Richard Modafferi at Audio Classics in June 2003. Very interesting - looks like it has an issue with frequency response. I tested a modern digital tuner (Carver CT-3) and it's frequency response checked out, so I know it's not an issue with the analyzer setup.

IMG_0133.jpeg...
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Running a Panasonic VP-8193 here with good results, along with a Rigol RF spectrum analyzer, a decent scope, and a couple of frequency counters (although the Panasonic is dead on.)
 
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I have a HP 8656B,8904A,11715A, amber 3501.
Good enough as long as it keeps running. At least I have the manuals, which for new equipment is not available anymore.
If you expect to use a scope for RF/IF measurements and troubleshooting, you probably need a fet probe for its low capacitance.
 
There's free computer programs available today to do aspects of tuner alignment. But these are not a traditional box. So, depending on the desire to "go there", may or may not work for folks.
I would also not recommend the tube based IG-37. Waste your time, you will, using this one. I had one, and wasted my time. That also goes for any tube based RF generator.

Skipped owning the SG-165, so never had that experience, but I'd say the IF sweep is probably the strong point. Most modern tuners using ceramic filters don't need that step in the alignment process though. If you do need sweep, there are other sweep generators you can use as well, most more dependable and modern.

I went straight to the ST-1000A, and then the ST-1020, then the Panasonic VP-8122. That's what I use today. The ST units are solid, well designed, and just work. But the limit is the lack of digital display, etc that you get with more modern generators.

Meguro, RE, and others also had great digital display generators if you can find them. In general, dedicated stereo generators will have better specs and functionality than a lash-up using an external MPX generator, but that usually depends on the generator FM specs. You need to look closely at the generators FM bandwidth and distortion. Most are good to 0.5%, which is fine for a lot of units, except the absolute best tuners with lower stereo distortion (0.03-0.05%).

The modern FM car radio adapters I've tested were pretty accurate for frequency. Thanks to mass produced cell phones, fairly precise crystal reference chips are common (cheap) now. And that's what's inside these FM adapters (at least the ones I tested).
So these can be a great economical choice, using USB stick based test signals, etc. They generate FM RF stereo signals, can be tuned in 100 kHz steps, have a digital frequency display, and allow distortion and separation adjustments that are "pretty good" - likely way better than an SG-165. You don't hook them directly to the tuner. For RF alignment, you place them far away to generate weak signals to a dipole antenna at the tuner. And then closer to generate strong signals for separation and distortion.

For distortion, an audio program like ARTA or REW that uses FFT for distortion. I've posted links to all this stuff here before, so search or ask here.

You should also get a decent scope, but most have that already, along with a multi-meter. A counter is also recommended.

The most expensive thing is really your time invested in reading, and watching videos on "how to". Than actually practicing on old simple stuff, like 3 gang solid state receivers or tuners with chip based MPX units from the 70's.
Bob
 
rcs16 said:
11715A
Click to expand...
I have a 11715A as well, have you found much use for it in tuner servicing? I assume you are using it with the 8904A and feeding a mpx signal to the 11715A for ultra low distortion tuner testing / distortion adjustments?
 
Yes that's my setup for low THD FM stereo. For very low THD mono adjustments, I use the Amber 3501 as a source. Use a JFW attenuator on the output of the 11715A. Have a 8901A modulation analyzer to get the modulation rate correct to 75KHz deviation.
Use the 8904A for testing amplifiers, everything but ultra low distortion, where I use an Amber 3501 for that. The 8904A with a new LCD is wonderful to use.
 
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I still have an SG165 left on the riser next to a VP-8121A rack unit converted for bench top. Either is sufficient to bring back a unit after a front-end or IF catastrophe, or if a technician has been in there with a Radio Shack color TV alignment set trying to adjust by ear just as the phone rings... The Sencore has had PS and oscillator repairs, plus the usual pot stem and L-pad issues. The Panasonic got a once-over cleaning and inspection while getting modded for bench top use.
 
There's a VP-8177A in my storeroom, sadly dead. The backup battery leaked and ruined the unit. Very localized damage, but enough. Just a heads-up to check inside your units before it's too late.
 
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