Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Aug Thu 18, 2022 8:20 pm


All times are UTC





Post New Topic Post Reply  [ 11 posts ] 
Author Message
 Post subject: Wave Generator questions
PostPosted: Jun Tue 21, 2022 11:48 pm 
Member
User avatar

Joined: Apr Wed 10, 2019 2:48 am
Posts: 779
Im woking on a Sine/Square Wave Generator. This was originally sold as a kit, and while it appears that the circuits I checked are correct, I have not gone through it in agonizing detail. I did however find a bad solder joint, an unsoldered wire, and a pinched/shorted wire that are all now corrected. I also replaced all caps except a few which tested ok on my leakage tester. OOT resistors were replaced, except the 1% resistors that I do not have, but were not off by much. I followed the cal procedure.

At power up, and using a fluke multimeter on the output, the hertz readings are all right on throughout the frequency (cps) range. However, when checking the Voltage Range im having trouble.

For example with Multimeter set to AC attached to the Sinewave outputs, and Freq (cps) oscillator dial fully closed, and Amplitude set full max, and Range set to 10V, I get the following results when switching the Frequency Multiplier Knob:

FreqMult knob at X1 = DMM reads 10.8vac
FreqMult knob at X10 = DMM reads 10.0vac
FreqMult knob at X100 = DMM reads 9.7vac
FreqMult knob at X1k = DMM reads 3.9vac
FreqMult knob at 10k = DMM reads 2.8vac

I believe that all Frequency Multiplier settings should give 10vac at the Outputs, since the Range Knob is set to 10V?

I have never used one of these generators before and was hoping that I could get some guidance on what I should be getting here. Could there be a limitation of my Dmm?

Thank You


Attachments:
7AE72E02-68A0-4EC4-A8E8-7F25158BB199.jpeg
7AE72E02-68A0-4EC4-A8E8-7F25158BB199.jpeg [ 317.91 KiB | Viewed 324 times ]


Last edited by Codepug on Jun Sun 26, 2022 3:28 am, edited 1 time in total.
Top
 Profile  
 
 Post subject: Re: Wave Generator questions
PostPosted: Jun Wed 22, 2022 12:44 am 
Member
User avatar

Joined: May Wed 18, 2011 1:40 am
Posts: 6371
Location: Littleton, MA
Codepug wrote:
Could there be a limitation of my Fluke 117 meter?

Your Fluke 117 is only rated for up to 1 KHz in AC Volts mode, and even then, the accuracy is degraded compared to below 500 Hz:
Specs:
https://dam-assets.fluke.com/s3fs-publi ... s-ds-w.pdf
Manual:
https://dam-assets.fluke.com/s3fs-publi ... 0000_0.pdf

_________________
Steve Byan https://www.byan-roper.org/steve/steve-at-play/


Top
 Profile  
 
 Post subject: Re: Wave Generator questions
PostPosted: Jun Wed 22, 2022 12:59 am 
Member
User avatar

Joined: Sep Mon 16, 2013 1:42 am
Posts: 5776
Location: Tucson, Arizona U.S.A.
Location: Tucson, Arizona U.S.A.
Quote:
I also replaced all caps except two multi cans (100uf,40uf and a 40,40,40,40uf) which tested ok on my leakage tester.

This isn't an adequate test. Although low leakage is necessary, correct capacitance and low power factor are also required. An electrolytic capacitor that has dried out will have low leakage but the capacitance will be very low and the power factor will be high. Capacitors like this won't work. This is the problem with the capacitors in a radio that hums when turned on. A capacitor with high leakage will overheat the rectifier/power transformer/something else. This is how repairmen in the old days got away with connecting a replacement capacitor across the failed one without disconnecting it. This trick doesn't work if the old capacitor has excessive leakage since then it is likely to short.

_________________
Jim Mueller

Who's that swimming in the punch bowl?
It's Walter Wart, the freaky frog!


Top
 Profile  
 
 Post subject: Re: Wave Generator questions
PostPosted: Jun Wed 22, 2022 1:32 am 
Member
User avatar

Joined: Apr Wed 10, 2019 2:48 am
Posts: 779
Jim, The tester showed capacitance higher. 100uf read 150uf and 40 read 50uf.
Will have to replace these anyway in time. Just trying to figure out how the device works.

Apparently, my dmm not rated for higher hertz. How would I measure the output for accuracy then? Would a 40mhz scope work ok?


Top
 Profile  
 
 Post subject: Re: Wave Generator questions
PostPosted: Jun Wed 22, 2022 1:38 am 
Member

Joined: Feb Wed 07, 2018 5:52 pm
Posts: 1314
Location: Stone Mountain, GA
Since the wave gen outputs only up to 1 mHz, a 40 mHz scope will work fine.

_________________
Scott.
Powered by infinite improbability drive.


Top
 Profile  
 
 Post subject: Re: Wave Generator questions
PostPosted: Jun Wed 22, 2022 2:52 pm 
Member

Joined: Jun Fri 19, 2009 5:34 pm
Posts: 12089
Location: Floral Park, New York
That was a pretty decent audio frequency generator in its day. It uses a Wein Bridge oscillator circuit with a lamp bulb used as the nonlinear element in the feedback loop to level the output. This is basically the same circuit that put Hewlett and Packard on the map in the early 1940s, and I am not sure but think Heath may have had to license it under HP patents.

Since the circuit is leveled, it should be capable of producing essentially the same output amplitude at the highest frequency that it does at the lowest. If not, you may have some weak tubes in there. A weak tube that still works at 50-60 Hz may not have enough emission to produce full output at 1-MHz, which is why tube testers are sometimes deceptive. But it appears the meter is the big problem here. If you had the tuning cap in the generator fully meshed, then on the x1 range it would have produced about 20 Hz. On the x10 range, 200 Hz. The meter seems to be reading those fine. It is about 10% off x100, or 2-kHz, which is not bad for a meter rated to 500-Hz. But quite predictably, beyond that it falls off rapidly. Your oscilloscope should handle these measurements with ease.

As for the metal can electrolytics, if their leakage and capacitance are in spec, I would not be in a big hurry to replace them. They will probably be okay for the time being. The AC loss (in terms of ESR, power factor, or dissipation) should be checked if possible. You will know when it is time to change them because the power supply ripple will increase, putting 120-Hz hum in the output, and/or the DC voltage readings will be off.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: Wave Generator questions
PostPosted: Jun Wed 22, 2022 10:07 pm 
Member
User avatar

Joined: Apr Wed 10, 2019 2:48 am
Posts: 779
I tested the AC waveform outputs with my scope, and they appear to be working accurately.

When testing on the DC output, the scope display agrees with the wave generators voltage setting, however, my Fluke meter once again throws me a curve. For example, 1Volt set on the wave generator DC side displays 1 volt on the scope, but approximately 500mv on the fluke.

I read that DC square waves should be measured with a volt meter that is true rms AND supports AC+DC. I dont believe that the Fluke 117 has the AC+DC feature, which may explain the inaccurate reading?

So, apparently measuring a DC square wave is different from measuring typical DC on the meter.


Top
 Profile  
 
 Post subject: Re: Wave Generator questions
PostPosted: Jun Thu 23, 2022 3:27 am 
Member
User avatar

Joined: Sep Mon 16, 2013 1:42 am
Posts: 5776
Location: Tucson, Arizona U.S.A.
Location: Tucson, Arizona U.S.A.
According to the schematic posted above, the sine wave output is AC coupled but the square wave output is DC coupled. So measuring the sine wave output with a DC meter should show zero for all frequencies and amplitudes. Doing the same test on the square wave output should show a DC value that varies with the amplitude setting of the generator.

_________________
Jim Mueller

Who's that swimming in the punch bowl?
It's Walter Wart, the freaky frog!


Top
 Profile  
 
 Post subject: Re: Wave Generator questions
PostPosted: Jun Thu 23, 2022 4:10 am 
Member
User avatar

Joined: May Wed 18, 2011 1:40 am
Posts: 6371
Location: Littleton, MA
Codepug wrote:
When testing on the DC output, the scope display agrees with the wave generators voltage setting, however, my Fluke meter once again throws me a curve. For example, 1Volt set on the wave generator DC side displays 1 volt on the scope, but approximately 500mv on the fluke.

I read that DC square waves should be measured with a volt meter that is true rms AND supports AC+DC. I dont believe that the Fluke 117 has the AC+DC feature, which may explain the inaccurate reading?

So, apparently measuring a DC square wave is different from measuring typical DC on the meter.

I presume the "1 volt on the scope" means 1 volt peak to peak. The square wave output of the AG-10 (the "DC output", as you call it) is directly coupled to the cathode resistor of a cathode follower. This means the square wave varies from ground to some positive voltage. There isn't any AC coupling capacitor on the square wave output. So, your square wave is 0 volts 50% of the time and 1 volt 50% of the time, as shown on your scope, right? Now the RMS value of that waveform is just 1/2 the peak voltage, or 500 mV, which is exactly what your Fluke 117 DMM reads.

_________________
Steve Byan https://www.byan-roper.org/steve/steve-at-play/


Top
 Profile  
 
 Post subject: Re: Wave Generator questions
PostPosted: Jun Thu 23, 2022 1:12 pm 
Member
User avatar

Joined: Apr Wed 10, 2019 2:48 am
Posts: 779
Thank you for clarifying my meter confusion. That makes sense to me now.
Time to get a better handle on square waves.


Top
 Profile  
 
 Post subject: Re: Wave Generator questions
PostPosted: Jun Thu 23, 2022 3:12 pm 
Member
User avatar

Joined: May Wed 18, 2011 1:40 am
Posts: 6371
Location: Littleton, MA
It can be confusing, as there are many ways to characterize the "voltage" of a time-varying waveform. There isn't a single definition of its voltage, and different instruments use different ways to measure the voltage.

For example, some (usually AC) VTVMs measure the average of the rectified waveform. Others (usually the standard DC/AC/Ohms service VTVMs) measure the negative peak, or the positive peak, or the peak to peak voltage. DMMs will usually measure the average rectified voltage, unless they have the RMS reading feature, in which case they will read the RMS voltage.

Moreover, many instruments use one method to measure the voltage, but then are calibrated as it they were using a different method. The typical service VTVM measures peak or peak-to-peak voltage, but is calibrated as if it were an RMS measurement of a sine wave. This is convenient if the input is in fact a sine wave, but can be quite confusing if it is not a sine wave.The typical AC VTVM measures the average rectified voltage, but again is calibrated in RMS volts assuming a sine wave input.

The best thing about a good calibrated triggered sweep oscilloscope is that it lets you actually see the shape of the waveform, so you can then select the appropriate type of measurement - RMS, peak, or average.

I think the VTVM books usually cover the different types of measurement fairly well, including showing how they can mislead you when measuring pulse waveforms.

_________________
Steve Byan https://www.byan-roper.org/steve/steve-at-play/


Top
 Profile  
 
Post New Topic Post Reply  [ 11 posts ] 

All times are UTC


Who is online

Users browsing this forum: battradio@, ITSJUSTB-RAD, MarkD and 18 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB