Signal Generators - choices

[rzenc]

Hi forum!

I'm interested in buying a signal generator for my bench and I'm new to testing gear, scopes and signal generators.. ... so if you don't mind my asking I would like to hear from you, among these signal generators, which would you choose and why.. these seems to have the lowest THD that is affordable by now...and they seem to be pretty alike... but as I said before.. I'm new to it and would like to know what wuold suit amp repair/building better...so which one would you guys pick up??


http://www.tequipment.net/pdf/Instek/GAG-810_manual.pdf

http://www.tequipment.net/KenwoodAG-204D.html

Thanks in advance! 

Best Regards

Rzenc

[tubesornothing]

They look darn near the same.  Anyways I look for low distortion (these are good), sine wave (all of them have it), a great big knob (these are good), and attenuator so you can get it down to guitar voltages (these look good).

The only thing I wish generators had was a larger range.  It  would be nice to have 50Hz to 20kHz in a single sweep.

[rzenc]

Thanks TON!

So... since they seem to be alike... I will go with the lower priced since the difference in price is around $200

.... when looking on a signal generator...what are your main concern? low distortion? If so...why?

Thanks again
Best Regards

Rzenc

[tubesornothing]

The big reason for low distortion is if you do signal analysis (spectrum analysis, FFT) it will be difficult to tell if the signal generator is generating harmonics or is it the tubes that are generating harmonics.  Found out that one the hard way...

[Fresh_Start]

AES offers this one for $140:
http://www.tubesandmore.com/scripts/foxweb.dll/moreinfo@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=S-MAFGEN

Seems to do the job ok.

There's some really good info on using one, and saving $$$ by buying a used one in this thread:
http://www.el34world.com/Forum/index.php?topic=7689.0

Cheers,

Chip

[sluckey]

I highly recommend this sig gen if it can be shipped to your location.

http://cgi.ebay.com/HP-204D-5Hz-1-2-MHz-Oscillator-Exceptional-Condition_W0QQitemZ290351516167QQcmdZViewItemQQptZBI_Signal_Sources?hash=item439a4c8a07&_trksid=p3286.c0.m14

It's item number 290351516167 in case the direct link gets trashed.

[rzenc]

The big reason for low distortion is if you do signal analysis (spectrum analysis, FFT) it will be difficult to tell if the signal generator is generating harmonics or is it the tubes that are generating harmonics.  Found out that one the hard way...

I have plans to buy Smaart and make an adaptor to make measurements like this...but now I believe a scope would help me more... althought I have seem some digital scopes capable of doing this signal analysis... but by now I guess it's beyond my compreenhension...

[rzenc]

AES offers this one for $140:
http://www.tubesandmore.com/scripts/foxweb.dll/moreinfo@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=S-MAFGEN

Seems to do the job ok.

There's some really good info on using one, and saving $$$ by buying a used one in this thread:
http://www.el34world.com/Forum/index.php?topic=7689.0

Cheers,

Chip

Thanks for both links Chip...actually I have been following the thread with great interest, since I'm about to spend $$$$$ on testng gear...

[rzenc]

I highly recommend this sig gen if it can be shipped to your location.

http://cgi.ebay.com/HP-204D-5Hz-1-2-MHz-Oscillator-Exceptional-Condition_W0QQitemZ290351516167QQcmdZViewItemQQptZBI_Signal_Sources?hash=item439a4c8a07&_trksid=p3286.c0.m14

It's item number 290351516167 in case the direct link gets trashed.

Unfortunately I saw it too late

However, I saw a 209 for 70$...what do you think Steve?


Thanks for the replies
Best Regards to all

Rzenc

[sluckey]

Unfortunately I saw it too late 

However, I saw a 209 for 70$...what do you think Steve?

I didn't think that one would last very long. If I didn't already have one, I'd have bought it on the spot. That was a nice unit.

209 is basically the same as a 204, but it also has a square wave output. They are both wien bridge oscillators. I'd prefer any of the older discrete component HP sig gens with a rotary range selector switch to the modern equivalents. I draw the line with the HP push-button selectors though, ie, 3312 and up. And I'm not interested in maintaining the old tube type wien bridge oscillators such as the HP 200 series, although I certainly understand why some tube nuts like them.

[tubesornothing]

If you want to do signal analysis (and not very many amp builders do), you can either do it by sweeping the spectrum with a signal generator or by feeding it white noise.  If you use a signal generator, you can either manually sweep the range or get a generator with a built in sweep.

However, it's not much use to sweep unless you have something to analyze the sweep with.  The cheap way is to pump the signal into your PC and use some cheap or free audio FFT software - there is lots of it out there.  Maybe an cheap way to see even if you want to play with signal analysis is to use your PC to pump out a sweep with some software, record  it to an MP3 then pump it through the amp.  Then use your PC audio card and some free scope software to capture the signal part way in and see what happens.  Fun to play with anyways.

A word of caution, if you are going to use your PC to capture the signal data you could possible be exposing your PC to high voltage - so be careful.

Anyways, if you don't what to do all that stuff, just get the HP generator Sluckey recommends, before I buy it!

[Rosser]

I tuned into this thread a little late...I just bought an audio signal generator to go with my new scope. I was looking to spend very little $$, so I bought an old Leader LAG-25 for <$20. One interesting thing I noticed about it is that besides sine and square waves, the selector has an icon for white noise. None of the other models seem to have this. Wonder if it will be useful.

Also, the guy I bought it from sent a Leader LSG-11 RF generator by mistake. It's a tube unit, but I tested it and it works fine, and the dial is even pretty well calibrated with my digital shortwave readout (within 5%). He offered to sell it for $9, so I bit. The audio generator should come today.

I bought this stuff for my guitar amps, sure, but also to work on an old Sansui receiver I recently got. I do like that HP audio generator -- maybe another time when I'm ready to spend a little more.

[tubesornothing]

Well with the white  noise you can put that into a stage, then hook a PC signal analyzer software on the output and see the frequency response of the stage.  E.g. tone stacks, filters etc.

[PRR]

> old Leader LAG-25

EXcellent machine.

If you tire of it, list it here.

FWIW: I'm moving, and won't take my too-large collection of "stuff". The sig-gen which I packed is an old Circuit Specialties 2001 function generator. It is based on the 8038(??) chip, meaning it makes triangles and then hammers them to "sine". The rated THD is only like 0.5%, but it's all in a "tit" on the sine tips, which makes a whine which is quite audible. No matter. For 'scope, I learn what it should look like, tips and all. For THD, either I'll want <0.01% hi-fi (which demands a special oscillator) or I will want an approximate >5% check (which I can do fine). And unlike my Heath and H-P wein-bridges, the func-gen sweeps smoothly. (And has TRI which is handy for clipping-checks).

[Rosser]

I had a chance to try out the LAG-25, and I think it will suit my purposes for the forseeable future. Nice, clean sine wave on the scope. The unit is almost mint, and the insides are really clean -- the dial is large and sweeps very smoothly. Those 60's Japanese electronics are pretty sweet, though not the industrial ruggedness of the HP.

The LSG-11 RF generator didn't come with probes -- it's the old F1 microphone screw-on style. I have a couple of volt/ohm probes like that for my Senior VoltOhmyst, but I don't want to cannibalize them. Maybe I'll convert the RF sig gen to BNC. However it leaks so much signal, I'm not sure it even needs probes to inject signal, at least not at the antenna terminals.

[Rosser]

...And unlike my Heath and H-P wein-bridges, the func-gen sweeps smoothly. (And has TRI which is handy for clipping-checks).

Question: I have heard that in the old days, guys used to "sweep" the frequencies manually, ie, jiggled the knob up and down. In a calibration of a radio that calls for sweeping, is this a viable operation to enlist a son or daughter? I obviously don't know much about sweep.