Alignment Tools?

Would anyone happen to recommend a good Signal/Function/Sweep generator that I can use for FM alignments as well as other things in my lab?

I was looking at this but also have seen people recommend the Sencor SG165

http://www.rigolna.com/products/waveform-generators/dg1000/dg1022/

Thanks for the feedback,

-RM

super98lsc said:

Would anyone happen to recommend a good Signal/Function/Sweep generator that I can use for FM alignments as well as other things in my lab?

I was looking at this but also have seen people recommend the Sencor SG165

http://www.rigolna.com/products/waveform-generators/dg1000/dg1022/

Thanks for the feedback,

-RM

Click to expand...

The maximum frequency for the one you have quoted is 20 MHz, so forget about using it for RF alignment. The SG165 is OK for older tube tuners with limited harmonic distortion specs but for high-end tuners, you need something more modern like an HP 8640B or a Signal technologies ST1000A.

I went through a rebuild of my SG165 because I could get the positive half of the 400 Hz waveform but not the negative. I get half the square wave and none of the RF signals. The design does not use adequate margins and in some cases will have negative margin. I checked the audio oscillator - excellent 400 Hz waveform there. Into the isolation and output buffer - still OK. The output of the output buffer? All wrong. R365 is a 390 ohm 1/2 watt resistor that will work if the TR316 FET, which is an MPF 102, has a low pinchoff voltage but not for one with a high voltage (but still within spec). The board was getting scorched under this resistor so I took it out and measured it - 2195 ohms. I have replaced it with a 390 ohm 1 watt and even that may be marginal. The minimum power will be 0.390 watts. The most it can see is 0.975 watts. Sencore apparently has no concept of derating or even doing the design properly.

This was not the only case. The power supply output capacitors run at 12 volts and are rated at 15 volts. In general, I use a derating of 60% for electrolytics where possible and any spike or circuit anomaly that will drive the voltage above 15 would kill the supply. I recapped the electrolytics in the power supply and RF board at the moment and I am upping the voltage rating on all the electrolytics. I am not sure if the MPF 102 that I have is bad or simply at the high end of the pinchoff voltage.

If you don't have the manual, it is free online at:

http://bama.edebris.com/manuals/sencore/sg165/

Getting this thing apart and putting it back together is like building a ship in a bottle, so I wanted to fix it once, get it right and have it work for the rest of my life. BTW I replaced R365 again with a 390 ohm 2-watt resistor.

Not bad for a meter I got for $10, but you have to be aware of the design errors. One worth noting is that the silkscreen for C4 on the power supply board shows the wrong polarity - the capacitor is in the right way around but the board markings are wrong. I am considering three-terminal regulators for the power supply - the current limit is set for 150 mA, so you don't need much and two electrolytics would disappear, including C4.

What you need depends on what you intend to align. If the tuner has ceramic filters you don't need to adjust the IF, so you don't need 10.7 MHz sweep capability. That's the main reason I have an SG-165; it has markers so you know where you are. It works very well for that task, but few tuners I work on need that capability.

You also need an MPX generator so you can adjust stereo separation. The SG-165 will do that OK too, though I use a Leader generator that's smaller and more convenient. I had never seen an SG-165 in person and was shocked at how big and heavy it was when the thing arrived. It takes up a lot of bench space, or you need a place to store it. Part of the process usually requires a frequency counter too.

As alluded to above, the SG-165 doesn't have the lowest distortion on the planet, so you may not be able to perfectly optimize THD on the better tuners. IMO, it's not as serious a flaw as one might think. Note that you also need a THD meter.

There is no single and affordable instrument for all FM alignment. The ST-1000A is probably great, but they too usually need service, don't come up for sale that often and cost quite a lot. Supply and demand.

The SG-165 is absolutely a PITA to work on. The bad cap markings are well documented, but I haven't heard many complaints about the component ratings. Some of the parts, like the output attenuator, are no longer available and you have to be creative with what you can get. IMO, it's made for a very specific purpose and isn't really suited as a general purpose signal generator. Note that the output amplitude is very small. Don't get me wrong; it was my first tool for alignment, it taught me a lot and does a decent job. It's just that rebuilding it was a major project and it's a service grade instrument, not lab grade.

There are other more modern units and you might want to research those- you'll find a list in other posts on the topic if you search.

I think the answers here already make sense - may I temporarily hijack the thread?

Conrad, did you happen to find a reasonable solution for the SG-165 attenuator? Like you, I'm thinking I might still use it for marker'd sweep, but the attentuator in mine is long gone. I poked around a little for external attenuators, but the ones I found tended to be more capable than needed, and much more expensive than I could justify.

Thanks,

chazix

Guys thanks for all the feedback.
The first one to align is this Sansui 5000x that I am working on. Its not so much "off center" , in fact on the dial its spot on and sounds amazing once a channel is tuned but the signal strength is very weak (always a 1 or less out of 5) and "Tune" meter is off center to the right whenever the channel is locked in. If I try to center it then the channel drops out. I know the guy who sold it to me supposedly re-aligned it and did some work on the RF strip because his poor soldering work is evident. Since I have restored and upgraded the entire power amp section and rebuilding the Tone control/Pre-Amp I would like the Tuner to be up to par. Since I am just getting back into my electronics fun I want to purchase "smart gear" that will last and serve the best purposes. My sole passion is Audio.

Actually more questions.... HP 8656B?
The reason I ask is I have access to surplus from schools/state deals where I can obtain the gear for use for nearly zero cost. In other words I could take 10 of them if needed, but I am not allowed to resell them etc. Just want to know which to look for. Of course the condition of them is un-tested and unknown. Usually just piled on a pallet type deal.

I think the HP would do you nicely for RF and IF stages, but it doesn't generate a stereo signal, so it won't by itself help you with adjusting multiplex decoders.

chazix

I have an SG165 and I bypassed the internal audio oscillator and brought the input to a new front panel BNC jack I installed. I connect it to the clean audio oscillator output from my analyzer and get much better performance from it. Now I can vary the audio level and frequency too! Other than that I've had 4-5 years of troublefree usage from it.

rBuckner said:

I have an SG165 and I bypassed the internal audio oscillator and brought the input to a new front panel BNC jack I installed. I connect it to the clean audio oscillator output from my analyzer and get much better performance from it. Now I can vary the audio level and frequency too! Other than that I've had 4-5 years of troublefree usage from it.

Click to expand...

Smart!

As for the output L-pad attenuator, mine was shot. I replaced it with a simple 100 ohm pot and it works fine. Impedance matching on receivers is much overrated in importance.

Never wanting to work on mine again, I replaced almost every cap in the thing with carefully selected and derated tantalums.

Another important thing is to make some new cables. The factory cables are too big and clunky. Good alignment requires not spraying RF signals all over the place, so a small cable that's shielded right down to the tip is needed to inject the signal when you have to do it at circuit level. The results are also much cleaner if you do the same thing when picking off signals going down the IF strip. Duplicate the factory diode probe, but shield it better and keep the exposed conductor to a minimum.

Okay, here's a wacky idea.

Let's say that someone decided that, for their needs, an instrument of the caliber of the Sencore SG-165 would be adequate. (For the OP's Sansui 5000x, it probably is.) I think there's consensus that one of those is going to require a certain investment in both money and time to get it working well.

What I'm wondering is if whether a Heathkit IG-37 might not actually be a better choice than the Sencore. It should be somewhat cheaper. I think it is at least as well documented. It's easier to work on. It has a light-bulb-stabilized linear feedback oscillator for the baseband audio tones, compared to the Sencore's diode-shaped square wave oscillator. It has a reactance tube modulator, compared to the Sencore's varactor (which I can't remember whether has some linearizing circuit or not). I wonder which one would actually produce a lower-distortion modulated signal?

With the Heathkit, though, you'd be giving up the AM generator, the 100-KHz-spaced post-injection IF markers, and some other probably-negligible capabilities of the Sencore (like the meters and rather puny dummy loads).

Your wildly speculating correspondent,

chazix

Thanks Conrad! Also great info you offer. I have some RG-174 cable so replacing the clunky stuff would be a nice upgrade. Chazix, I'm enjoying your thought provoking input too! :thmbsp:

Was the Heathkit factory built only or also available as a kit? I'd hate to get a kit built one, fearing poor workmanship. Did they use factory numbered semiconductors or standard numbered ones? The former would make it tougher to service them.

The Heathkit IG-37 was for sure available as a kit. That's one of the reasons that I say it's well -documented, because you can find the assembly manual online. I don't know whether factory-built examples were available.

Don't know if this will cause a loss of all interest, but the Heathkit has very few semiconductors, whether factory- or standard-numbered. That's right - it's a tubed unit!

Perhaps my age is showing, yet again...

chazix

Nothing wrong with tubes- I still use my tube-filled boat anchor scopes every single day. The IG-37 could be just fine- I don't know how common they are. There were recently several Fisher alignment generators (rare) sold on eBay and I was surprised at how little one of them went for. AM shouldn't be a big issue. Anything that make signal, say a station, will let you set the dial. There should be an IF shape, but peaking it usually gives OK results if you don't care about AM fidelity, if there is such a thing.

This is what I use, and is a pretty decent piece: https://www.atecorp.com/ATECorp/media/pdfs/data-sheets/Leader-3215-16_Datasheet.pdf

They come up on the auction site periodically.

Enjoy,
Rich P

Ooh, now that is NICE! Great, now I want one.

Definitely nice. There are some others that are similar but I've never seen a downloadable manual/schematic, and I wonder if they can be fixed should they break; do they have a lot of custom ICs?

That Leader is nice... I should be able to calibrate satellites with that

rBuckner said:

Ooh, now that is NICE! Great, now I want one.

Click to expand...

This or similar comes on ebay often. But get ready to spend about $1000. So it makes sense only if gear you are fixing is 2x-3x more expensive, or you expect do alignment job on a regular basis.

I have a Heathkit IG-37 and its predecessor, the IG-112. They have semiconductor diodes and tube active stages, so it is from a period in electronics where equipment was easy to understand. Of course, being Heathkit meant it was easy to assemble and disassemble, the opposite of the SG-165. Schematics for Heathkits have dried up on the net because the copyrights were sold to someone who apparently is in business selling them. But some pages still exist, you just have to dig for them and maybe hit the wayback machine. I got the IG-37 for $15 and the IG-112 for either $5 or $10, I forget which. Neither of them have voltage regulation, so they should be regarded as service instruments only, a step lower than the SG-165.

There are software options for MPX generation if you have a sig gen that will do the proper RF output and accepts AF input. I found a plugin for Winamp called Stereo Tool that will lay in the proper pilot tones and whatnot. I tried it out last night, feeding from my computer sound card into my HP 8640b. The shop stereo went to FM stereo and did what you would expect.