Products > Test Equipment
Racal Dana 9083N Two-tone Generator - Pictures, Questions
wn1fju:
Picked up a Racal 9083N two-tone generator (0 - 20 kHz) for $30 USD. These things presumably were used to test a device's intermodulation distortion. Preliminary testing shows that it works fine and both oscillators have distortion less than -80 dBc (at 1 kHz).
The build quality, as shown in the pictures, is outstanding. It's hard to see, but most of the electrolytic caps have foam cushioning underneath. The op-amps have plastic cradles, the wiring is neatly tied and routed, the front panel potentiometers big and beefy. I have several other Racal pieces, and the manufacturing quality is nowhere near this one.
But perhaps that is because Racal actually didn't make this piece??? You will note that the board is marked "KDP Electronic Systems." Maybe one of the British eevBlog members can share some light on Racal and second sourcing products.
Also, there are about 16 adjustment pots in this unit. How can I resist turning some? If anybody has either the service manual or the adjustment procedures, please send me a message. Thanks.
RolandK:
Looks like classic wien bridge oscillators, eg. arround IC 9: C49 to C51 and C52 to C54 the switchable high- and lowside Capacitors, the black part the thermistor for amplitude regulation.
RV 18 and RV 19 perhaps for the calibration of the left wien bridge arm to voltage relation and frequency, RV20 for amplification.
You must turn RV18 and 19 togeher to adjust frequency without changing amplitude. As it seems to use equal capacitors the opamp input should see 1/3 of the output voltage.
wn1fju:
Thanks for the reply. I had surmised that they must be Wien oscillators given the low distortion that I am seeing.
The unit seems in perfect adjustment, but I hooked the 9083N simultaneously to a scope, counter, spectrum analyzer and distortion analyzer and started twiddling the pots (after I marked their original positions). As you said, slight changes in frequency and/or amplitude. I was hoping to drive the distortion even lower, but these Wien oscillators aren't like diode-shaped triangle waveforms that one finds in a lot of function generators which do have to be adjusted to achieve low distortion, so I wasn't expecting success.
ch_scr:
You should read "Max Wein, Mr. Hewlett and a Rainy Sunday Afternoon" by Jim Williams - a copy came up on google
It's quite the nice read and explores the possible improvements.
factory:
--- Quote from: wn1fju on November 09, 2023, 02:17:51 pm ---
But perhaps that is because Racal actually didn't make this piece??? You will note that the board is marked "KDP Electronic Systems." Maybe one of the British eevBlog members can share some light on Racal and second sourcing products.
--- End quote ---
KDP are still around, unlike Racal...
If you keep clicking "load more images" there is something that resembles the 9083.
https://www.kdpes.co.uk/kdp-gallery/
Racal would have filled it bead tants >:D if they had made it.
David
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