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HP 339A oscillator problem
HP 339A oscillator problem
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Old 1st August 2018, 02:51 PM   #121
BSST is offline BSST  United States
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I share your hope a forum member has some useful link.

Just two or three days ago, I did stumble into this very fascinating bit from the engineer at HP who designed the notch filter in the 339A--- fellow by the name of Joel Nesheim. His post is in the reader-comment portion of the link below. I don't know if he could be tracked down and might respond to a direct appeal.

Measuring Distortion with a HP 339A and a Keithley 2015 THD | gerrysweeney.com

Good luck.
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Old 1st August 2018, 02:54 PM   #122
BSST is offline BSST  United States
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Measuring Distortion with a HP 339A and a Keithley 2015 THD | gerrysweeney.com

The link didn't past very well. This may be no better.
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Old 1st August 2018, 02:56 PM   #123
BSST is offline BSST  United States
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Measuring Distortion with a HP 339A and a Keithley 2015 THD | gerrysweeney.com

Third attempt.
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Old 1st August 2018, 03:00 PM   #124
BSST is offline BSST  United States
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404 Not Found

Joel Nesheim on August 11, 2014 at 2:07 am said:
Thank you for the video of the 339a distortion analyzer. I watched the tear down video as well. It was a trip down memory lane for me since I designed the notch circuit (part of which is on that large circuit board in the back that you had some trouble removing.

That board kept me awake many nights. By the way, both the notch circuit and the oscillator ciercuit are based upon the “bridged T” notch filter which is tuned by the resistors and capacitors chosen by the wafer switches, then fine tuned by two photodiode/LED modules.

I spent weeks doing calculations comparing the responses of Wien bridge, twin T, phase shifter, and bridged notch circuits before I chose the bridged T configuration.

The biggest headache was the slower speed of the auto null circuit as the frequency to be measured approached 10 Hz.

Production started in 1977 I think and I followed the 339a into production which was a very busy and frustrating time for me. You end up reporting to several bosses at once and their objectives may differ.

The oscillator and input circuits were designed by Fred Kitson and the power supply was designed by the project manager, John Manning.

Design and production were done at HP inLoveland Colorado. The 339 was later produced at HP in Japan.

Best regards, Joel Nesheim

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Obviously, I still don't know how to generate a link. ;(
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Old 1st August 2018, 03:06 PM   #125
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HP 339A oscillator problem
Measuring Distortion with a HP 339A and a Keithley 2015 THD | gerrysweeney.com
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Old 1st August 2018, 03:39 PM   #126
BSST is offline BSST  United States
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Thank you, jazbo8. The link was working all along. I was just too thick to recognize the fact.

I senior moment, perhaps.
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Old 10th August 2018, 01:18 PM   #127
microx is offline microx  Spain
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Default progress--kinda

Fitted the two quadamps to A4 board and,

Before with an external osc I had a null when 339A was set to 1kHz and the osc was at 860 Hz, now the null comes at 1,160Hz.
on and off null
Using the internal osc I can get a null using the osc Vernier at max clockwise, frequency measured at 1,160Hz.

In CAL position the internal osc frequencies are very close to perfect.

A4 board-

TP5, TP3 equal amp sine waves
TP4, sine wave with greater amp, lower with null
TP1, on null 3.25vdc, off null 1.2vdc . slow rise and fall
TP2, on null 0.45vdc off null 0.65vdc
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Old 10th August 2018, 03:33 PM   #128
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Hi Microx. I hoped no news was good news.

Using external oscillator, I'd like to study behavior around A4 TP2, and U5 pin 9. These two voltages should always be equal, irrespective of quality of the null.

Assuming this is found to be the case, would you advise the behavior of TP2 at below the null frequency, at null, and above the null frequency? Any associated frequency arrow activity?

You might explore U3A pin 1 versus U5A pin 1. I think they should roughly similar waveforms when the instrument is at null.
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Old 11th August 2018, 08:50 AM   #129
microx is offline microx  Spain
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A4 board, TP2 8.62vdc, U5 pin 9 10.64vdc.
TP2 bellow null -0.714vdc
at null 7.4vdc
above null 8.73vdc
U3a pin 1 has a waveform like sawtooth with rounded tops
U5a pin 6 has no waveform
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Old 11th August 2018, 08:55 AM   #130
microx is offline microx  Spain
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It is not all bad news, before I had a null bellow the 339a settings now it is above. This tells me that the switches and passive components in the null circuit are OK, any fault there would not show bellow and above.
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