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Taking A Dip Into The Tuner Alignment Game- Advice?

tybrad

tybrad

Lunatic Member
Banned
Hey,
I am ready to begin doing tuner alignment. I know that I need a 'scope, which I have access to. But what do I need to look for in an RF oscillator? I have seen one with a single, fixed freq. of 10MHz, others are variable.

For AM, is using a 'scope and oscillator easiest, or just with a voltmeter?

Thaks for any buying advice you can offer.
Tyler
 
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Check out PunkerX's sticky in the tuner thread. It details everything you'll need.

The FM Signal generator, Counter, and Dummy antenna loads are a must have in addition to the scope/DMM and so on
 
Yeah, I did not see it. Sooo, back to the regularly-scheduled question...

Red- thanks for the additional info.. and I'm still lookin' for more.
 
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There are several ways of going about it. Here's what I did and why-

1. good scope (tek 465 with 100 MHz BW and x-y capability)-- to visually center and make symmetrical the FM detector transfer function, plus use it to synch one waveform with another (19 khz pilot for instance). Also used to observe signal flow in case there is a problem with the unit besides being out of alignment.

2. good dvm

3. good fm signal generator to provide unmodulated and modulated RF to the receiver front end. I use a SG165 Sencore, but the ST1000A is better. This stereo generator needs to provide unmodulated, L/R mono, and LR stereo MPX signal to RF modulator. Also, tunable over the broadcast band is best, and modulation (composite to RF) linearity is important for analyzing tuner distortion and adjusting it to min value. Also does not hurt if you have a way to verify % modulation, if it is not calibrated, and a way to measure or understand the RF level being output, to see if you are in the ballpark (+-1.5 dB or so) with sensitivity specs.

If this generator has a 10MHz I/F sweep mode, then you can optimize the alignment of the I/F stages.

4. A low noise (distortion) sine wave oscillator to drive the stereo generator. I modded the SG165 to take and external source (Wavetek 180). The wavetek worked well after being on for about a month driving a 50 ohm load, then going through the sine wave distortion cal on it using the HP LF spectrum analyzer to minize the 2nd and 3rd order products. I run it at 1KHz. If I change the output level a lot or the frequency from 1Khz to 10KHz, I have to re-optimize it, since it is more a function generator than a sine wave generator. But I can keep harmonics down to below -70dB with it.

5. A way to measure the audio distortion out of the FM detector. I use an HP 8556A LF plug in for the HP141T spectrum analyzer for this.

6. A way to look at the raw RF coming into the tuner under test, before and after amplification (to measure levels and modulation index), the noise of the local oscillator (for grins mostly), and the I/F chain envelope. I use an HP 8553B spectrum analyzer RF plugin for this.

7. Good resolution frequency counter. I found an HP 10 digit counter, oven stabilzed, at a local ham meet. It is not sensitive enough to measure RF freq directly from the SG165, but it can measure the output frequency of the I/F, the LO, and the RF after single stage amplification. I use it with the tracking generator function of the analyzer, to know what freq value I'm looking at on the display, since it is old school, and does not annote this on the screen. I also use it to set 19 KHz MPX functions when required.

8. A bunch of bnc cables, adpaters, and loads to terminate things properly.


That's a lot of stuff that has to work properly to fix or optimize a tuner needing assistance, but it is an addictive hobby, more so than recapping units...

There are some good textbooks on the subject also, but I don't have any links handy.

Get a cheap GW tuner from the '70s to start. Get a couple more, and then you will be sucked in.
 
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Huh...I'll have to find it.

Maybe it's a more general "so you think you wanna be a tech"

Easiest place to start is to pick up the service manual for any tuner you're considering working on. It will list in detail the tools required.

An example- In the Kenwood L-07T manual it calls out the following items:

Test Equipment and Their Specifications

Audio Signal Generator (AG)
Ranges: 5 Hz- 500 kHz
Waveform: Sine Wave
Output: 10V RMS
Distortion: 0.01% or less

Solid State Volt Meter (SSVM)
Ranges: 0.3 mV- 100V (full scale)
Frequency Response: 5 Hz - 500 kHz
Impedance: 1 M Ohm or more

Standard Signal Generator (RF-SG)
Ranges 90 MHz- 108 Mhz
Modulation Frequency: 1 kHz, 400 Hz or External Input (Input Level 2 V or less)
Deviation: 0-150 kHz
Output: 100 mV or more
S/N Ratio: 85 dB or more
Distortion (Internal): 0.5% or less

Oscilloscope:
Ranges: DC-10 MHz
Sensitivity: 20 mV/cm
Impedance: 1 MOhm or more

Multiplex Signal Generator (MPX-SG)
Modulation Frequency: 1 kHz or External Input (input level 5V or less)
Separation: 60 dB or more
S/N Ratio: 85 dB or more
Preemphasis: 50 uS, 75 uS, and 25 uS (u indicates" micro")

Frequency Counter (Counter)
Frequency Response: 10 Hz- 1 MHz
Sensitivity: 50 mV or more
Impedance: 1 MOhm or more

Distortion Meter
Ranges: 0.1%- 0.03% (full scale)
Sensitivity: 100 mV or more
 
redcoates7 said:
Easiest place to start is to pick up the service manual for any tuner you're considering working on. It will list in detail the tools required.

An example- In the Kenwood L-07T manual it calls out the following items:

Test Equipment and Their Specifications

Audio Signal Generator (AG)
Ranges: 5 Hz- 500 kHz
Waveform: Sine Wave
Output: 10V RMS
Distortion: 0.01% or less

Solid State Volt Meter (SSVM)
Ranges: 0.3 mV- 100V (full scale)
Frequency Response: 5 Hz - 500 kHz
Impedance: 1 M Ohm or more

Standard Signal Generator (RF-SG)
Ranges 90 MHz- 108 Mhz
Modulation Frequency: 1 kHz, 400 Hz or External Input (Input Level 2 V or less)
Deviation: 0-150 kHz
Output: 100 mV or more
S/N Ratio: 85 dB or more
Distortion (Internal): 0.5% or less

Oscilloscope:
Ranges: DC-10 MHz
Sensitivity: 20 mV/cm
Impedance: 1 MOhm or more

Multiplex Signal Generator (MPX-SG)
Modulation Frequency: 1 kHz or External Input (input level 5V or less)
Separation: 60 dB or more
S/N Ratio: 85 dB or more
Preemphasis: 50 uS, 75 uS, and 25 uS (u indicates" micro")

Frequency Counter (Counter)
Frequency Response: 10 Hz- 1 MHz
Sensitivity: 50 mV or more
Impedance: 1 MOhm or more

Distortion Meter
Ranges: 0.1%- 0.03% (full scale)
Sensitivity: 100 mV or more
Click to expand...


Pretty much what every DIYer has under his bench. :no:

And, of course, you need to know how to operate every one of those pieces of equipment, what they do and why, and how to interpret the results when the results are not as expected, so you know what to do next to correct the anomalies.

There's another small, "oh-by-the-way"...it's not at all uncommon for there to be errors in the alignment instructions, particularly on vintage gear going back to the early MPX days.
 
fisherdude- EXACTLY! Proper alignment of a tuner is not for the faint of heart. You may stumble into good results without the right tools, but not on a consistent basis.

I'll take on a lot of repairs, but I still send my tuners to a tech with the right gear (and the knowledge to use it) for alignments

That said, I strongly believe that anyone who's going to get into repairing/restoring their own gear should some day invest in an audio signal generator, an oscilloscope, and a good DMM. If there's any doubt on how to use ANY of these tools, get some training. I started with a Radio Shack "how to use your meter" and progressed from there.

Repairing and restoring gear can be a lot of fun, but if not done properly (or done with the wrong tools) it's a great way to start a boat anchor collection!
 
Just a quick suggestion for anyone who's interested in learning this skill:

Start with a plain AM radio. Buy some $20 junker that works, get a signal generator and a decent DMM, and have a go. When you understand what you're doing, and you can take an AM radio, follow the alignment instructions, and the radio works better after your futzing than it did before, then...

You're ready to tackle an ordinary FM radio or a mono FM tuner. And you'll need more equipment. Once you know what you're doing with mono FM, then, and only then, should you consider trying your new skills on an FM MPX Stereo tuner.

And then you'll need the full list of equipment from ericson38's and redcoates7's posts above.
 
Dmm is too inacurate for am, vtvm is the way to go. I tried with the dmm and it bounced aroubd too much, ended up using a scope. Am is not difficult, its fm that's the challenge, my scope is only a 40mhz so I'm out for fm, for now.
 
It's not that a DMM is inaccurate, the input impedance is plenty high. The issue, as you've noted, is that an analog meter is sooooo much easier to read when you're trying to peak a reading.
 
Alright, alright. You guys have made me rethink this venture. For the limited tuners I would be working on, it's probably not going to be worth the time and $$ investment.

I am thinking of possibly apprenticing with a local audio repair guy to occupy some of my summer- he just does not know it yet.
 
If you can find somebody to teach you this stuff, it's the best possible path. I'd give my right arm for somebody I could work with.

Unfortunately, while so many people are lamenting the fact that these skills are dying out because nobody wants to learn, the old experts don't want to help anybody become competition.

:dunno:
 
10 mhz isn't gonna do it for FM. The IF strips are almost all 10.7 mhz, so you need at least that much bandwidth on the sweeper, scope and freq counter. Having something that will run up to 100mhz is really nice, but not critical. There are broadcast stations on the air that you can use for the RF and oscillator alignment if needed, and they're quite possibly more frequency accurate than your test equipment anyway. Not supre likely you'll need or be able to tie the scope in directly to the oscillator or RF amp anyway, so most likely anything you'd see on that is 10.7mc, audio, or MPX frequency related.
 
There was a post a few years back that dealt with what the average Joe could do, as far as tweaking a tuner. It was a simple no nonsense type of thread that explained a few steps a person could do to help the alignment of a tuner without going to the lengths of getting all the tech equipment. I wish I could find it again but searches have not turned up the thread I remember. Draudio's tuner cleaning thread is very informative and often time, following his advise, will improve your tuner's performance. If anyone knows this thread, please post it here.
 
It is that complicated on the fm side. Wanna do some interesting reading, go download the Dynaco fm-3 manual, it's all done by the tuning eye and its very long. I've read that it has taken 2 plus hrs to align the the first time, the am radio I did took over an hour which involved soldering a cap to a tube socket for one of the stages. This is tube, imagine a 70's receiver?
 
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