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-   -   Older signal generators worthwhile? (http://www.diyaudio.com/forums/equipment-tools/207634-older-signal-generators-worthwhile.html)

JZatopa 27th February 2012 04:14 AM

Older signal generators worthwhile?
 
So I am in the market for my first signal generator and I really don't have much money to spend. My options are to use an old CD player with a burned CD or there is someone selling a Heathkit Signal Generator IG-82 and a EICO 377 in my area. Are the vintage pieces worth the time or should I just use the CD player?

cyclecamper 27th February 2012 04:45 AM

...or one of the Behringer EQs that also incororates a signal generator. Works for me.

What do you want it for? Do you need a perfect sine? Do you need two? Do you need perfectly consistent amplitude as you sweep? Do you need computer control? Have you considered your PC's sound card? Do you need perfect pink? Audio only or RF too? Do you need accurate frequency or do you have a frequency counter? Do you need any clock or digital trigger outputs?

I've regretted giving away an old old HP...What can I say, I just dig big dials LOL.

head_unit 27th February 2012 05:32 AM

We once tested a bunch of digital generators ALL of which had too much distortion to test woofers with. I ended up with a used old analog big-dial type.

So the old ones might be good, OR they might not work properly. You need a way to test the generators and measure their distortion.

I also concur: what do you want it for?

JZatopa 27th February 2012 04:03 PM

I am looking for one to do basic tests on amps, preamps, etc. I have an o-scope but no signal generator to use with it to test with. I recently build an F5 amplifier that I want to measure to make sure that everything is working perfectly and within spec. I also have a few other amps and preamp I would like to test and modify and need a way to measure what has changed. I don't see myself using a frequency generator often enough to warrant spending a lot of money, but I do need something that is functional.

Unless you can use an oscope to test the distortion of a frequency generator, I have no way to test them.

Speedskater 27th February 2012 11:26 PM

I often use a CD player with a test tone CD as a signal generator.
You can use your PC sound card and a program like RightMark to test for distortion and frequency response.
Hint: Don't use an expensive sound card until you have all the test procedure and power amplifier bugs worked out.

head_unit 29th February 2012 01:43 AM

You can use the scope to mostly check the output of the frequency generator, at least to see if there is gross distortion. Low levels like a couple percent may not be obvious visually.

This might work:
LEADER MODEL LAG-120B AUDIO FUNCTION GENERATOR 10 HZ TO 1 MHZ | eBay
which another site says is replaced by
Instek GAG-810 Audio Generator Low Sine Wave Distortion GAG810, GAG 810

But if you don't need precise frequency adjustment then CDs might work just as well.

In neither case can you really tell what's happening with distortion other than on a gross level. The generators are supposed to be low distortion, but if used and old can have gotten out of calibration, broken transistors, etc

JZatopa 29th February 2012 02:13 AM

The guys selling the signal generator only wants $15. I figure it might be worth a shot.

I just found a guy selling a function generator in the area. Is that able to do the same job?

jackinnj 29th February 2012 02:33 AM

You'll occasionally find Hewlett Packard 200 series generators for $20 on EBay. Other high quality units that don't seem to get a lot of attention are Krohn-Hite, GenRad (General Radio), B&K, Fluke.

Enzo 29th February 2012 06:04 AM

I found an old HP 200 series for $5 at the local university salvage. Bent plate on the tuning cap was all that was wrong with it. Old as the hills, but still makes fine sine waves.

JZatopa 1st March 2012 06:01 AM

Well I picked up 2 signal generators for $15. Turns out they are both tube. Only one works. I am not quite sure why the other one doesn't. It shows literally nothing on the o-scope so I am guessing something is loose on the inside. The working one isn't perfect but it gives me a signal.

If I wanted to recap either of these is there any problem with using cheap modern caps as long as they were of the proper V rating?


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