[SOLD] FS: [US] $119 Tektronix 191, Constant Amplitude Signal Generator - Page 1
Forum section: electronics / general

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: October 30, 2023, 07:17:47 pm
content: Hello everyone, I'm here to sell my Tektronix 191 Constant Amplitude Signal Generator. It's conditions seems to be fine and it works pretty well. Hoping to get $119 out of it.I also have an eBay listing for it here:https://www.ebay.com/itm/166322388176?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=CTI57OxBQDq&sssrc=4429486&ssuid=CTI57OxBQDq&var=&widget_ver=artemis&media=MOREI'll insert the listing description here:Brief Description:This is a Tektronix Type 191 constant amplitude signal generator. It can output 50kHz and 350kHz-100MHz sine waves at calibrated Pk-Pk amplitudes.As seen in the last few images, it works very well, but I can not guarantee it works perfectly because if it's age.However, from what equipment I do have, amplitude accuracy on for frequencies below 50MHz seems very accurate. But going above that, the amplitude seems to be going up? This may simply be poor quality cables or that fact that the 50 ohm termination happens right at the output. of the generator and not the scope input. Using a Tek 475 with a very much direct connection gives perfect results.Frequency accuracy is the best I've ever seen considering it uses an analog dial. Set it exactly on 4MHz on the dial, outputs almost exactly 4MHz. My scope is not the best so it's very likely the scope is off in frequency and not the Tek unit.This unit was tested mainly on a Tektronix 2230 100MHz oscilloscope and a Tek 475.What You'll Receive:You will receive the Type 191, a frayed electric power cord, and a Tektronix PN: 017-0083-00 GR to BNC adapter with built-in 50 ohm termination.You will not receive the oscilloscope. I've had a buyer in the past argue that they thought a BK Function Generator came with the oscilloscope. Again, you will not receive the oscilloscope or any kind of oscilloscope.Testing:If you do end up buying this unit, and are meeting up, you are welcome to fully test it yourself if you want to. You may bring your own test equipment. I have a couple oscilloscopes myself I could bring out.Cosmetics:For cosmetic condition, please look at the photos. Personally, I think it looks quite alright for being almost 60 years old.Other Stuff:Please do your research on this unit before considering buying it. There is a wonderful Tektronix wiki about all sorts of Tek equipment called w140. Has manuals and everything there, for free!Price is negotiable so don't hesitate to reach out. I will offer a $30 discount for engineering students. However some kind of proof will be required.This could be used as a good old signal generator, a function generator, even though it only really... well... has one function. An oscillator, because that's what it is, or a calibration standard. Good to calibrate oscilloscopes. Or create sinewaves on an oscilloscope.This is where the eBay description ends. But here I'll make another offer. If you can come and pick it up yourself without shipping in Sacramento, California, you get to pay only $100. But then the student discount is reduced to $25.I'm just trying to free up some space on my workbench... and get some extra cash, only to inevitably buy 2 more pieces of test equipment to fill up even more space.I have 2 of these and I'm hoping to keep the other one for myself as it's in a slightly better cosmetic condition and I already recapped, and refurbished it. However, for the right price, I can sell that too.Edits made reduced price from $149 to $119.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: October 30, 2023, 07:19:20 pm
content: Whoops, looks like the images didn't upload properly. Here's the front photo. I'm too lazy to post the rest here. The rest of the images are on ebay.

author: TimFox
author_rank: Super Contributor
timestamp: October 30, 2023, 07:49:13 pm
content: Out of curiosity, what is the subsystem used to keep the amplitude constant?Is it a thermal converter?

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: October 31, 2023, 12:16:41 am
content: Quote from: TimFox on October 30, 2023, 07:49:13 pmTo answer your question TimFox, all I did was look at the manual and find the Theory of Operations section of it. I really like the old Tek manuals because they have everything you could have possibly needed to know about their instruments. The manual I used can be found here,https://w140.com/tekwiki/images/1/18/070-0522-00.pdf, and here's a quote taken directly from the manual.Comparison VoltageThe DC voltage from the Comparison Voltage circuit applied to the Peak to Peak Detector determines the Oscillator output signal amplitude applied to the 50 ohm Wideband Attenuator.Peak to Peak DetectorThe output of the Oscillator and the Comparison Voltage are compared in the Peak to Peak Detector and any necessary correction voltage to correct the output signal amplitude is sent to the Feedback DC Amplifier.Feedback DC AmplifierThis amplifier receives the correction voltage from the Peak to Peak Detector and then Supplies the amplified correction voltage to the grid of V94, the Series Regulator Tube.End quote.The much more detailed description can be founded in the manual as well.

author: jonpaul
author_rank: Super Contributor
timestamp: October 31, 2023, 02:52:48 pm
content: Wonderful unit, almost got one in 1971 for ADC/DAC work.An old one from a Ham Flea or Sil Valley sale still works!The TEK SG503, is a modern equiv rarely last longer than 10 yrs.Jon

author: TimFox
author_rank: Super Contributor
timestamp: October 31, 2023, 04:08:19 pm
content: To BlownUpCapacitor:I don't have the manual. Is the "peak-to-peak detector" two vacuum diodes or two germanium diodes or something else?That is what I was asking: obviously the output of the detector is compared with a reference in a servomechanism to control the output.Similar systems from Hewlett-Packard used a thermal converter: comparing a thermocouple heated by the AC output to a matched thermocouple heated with DC to measure the RMS output over a wide frequency range.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: October 31, 2023, 06:31:57 pm
content: Reply to TimFox:The peak to peak detector seems to be composed of two diodes, D67, and D60, and a few passive components. D67 and D60 are two GaAs diodes, and according to their description, glass diffused?This Peak to Peak detector provides a DC voltage to the DC feedback amplifier that represents the difference between the comparison voltage and the actual, peak to peak signal output of the oscillator.Anyways that's the peak to peak detector.This peak to peak detector outputs a DC voltage to the DC feedback amplifier and that feeds a signal to the grid of V94, which controls and regulates the amount of plate voltage V10 gets, which can be used to regulate the output amplitude of the oscillator. V10 is the oscillator tube.I've included some schematics. The full manual can be found with this link:https://w140.com/tekwiki/images/1/18/070-0522-00.pdfOr by visiting w140.com and searching for the Tek 191 manual.I can attach some screen shots of the Theory of Operations here if you'd like if you're having trouble accessing the file.Edit: Edit was made to correct mistake of "feeds a signal to the plate of V94" to "feeds a signal to the grid of V94".

author: TimFox
author_rank: Super Contributor
timestamp: October 31, 2023, 07:16:19 pm
content: Interesting. I didn't realize GaAs diodes were in use at that time (1966).The good description of the circuit action (typical of that bygone era) estimates the forward voltage of each diode at 0.6 V, which is more typical of Si, but GaAs was novel then and that voltage cancels out in the circuit.

author: alm
author_rank: Super Contributor
timestamp: October 31, 2023, 09:38:53 pm
content: Quote from: jonpaul on October 31, 2023, 02:52:48 pmI'd love to see the data you base this statement on. The SG503 was discontinued in the early eighties in favour of the TM5000 series of scope calibration plugins, so if the half life was less than 10 years, then the number of still functional units would be basically zero. My anecdotal evidence conflicts with this.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: October 31, 2023, 10:49:56 pm
content: Reply to alm:The SG503 was discontinued in the early eightiesDid you mean to say early nineties? w140 says discontinued 1993.

author: jonpaul
author_rank: Super Contributor
timestamp: November 01, 2023, 07:39:53 am
content: Rebonjour,Blownup: YES SG503 current till 1993 , sorry!Alm: I had ~ 6 pcs SG503 since 1990s. I have no evidence besides my own experience.All mine (early models non -A) developed one or more bad bands (readout blinks) due to the type of cam bandswitch used. Switches can be cleaned but are not reliable in the long run.See groups.io Tekscopes and Tekscopes and TM500.Besides the bandswitch, 2 or 3 SG503 are still working.My 191 is 100% !Jon