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]

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.

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  if they had made it.

David

[wn1fju]

To member "ch_scr":  Thanks for the link to the article.  I might be tempted to play around with one of the oscillators in the 9083N if only I had the schematics and parts list.  I don't want to try and reverse engineer it first.  Besides, I am measuring 0.01% (-80 dBc) distortion (@ 1 kHz) on my HP 8903A which is the specified performance value.  If I really need something better, I also have an HP 239A and that measures 0.0016% (-98 dBc) distortion.

To member "factory":  I did find the picture.  The resolution isn't high enough to read the front panel, but I could see the lettering "Racal Dana" on the side panel.  And yes, I've been there, done that, when it comes to exploding/burnt/shorted tantalum caps in Racal equipment.  Not that the caps Racal used were any better or worse than any other test equipment manufacturer of that era...

[TimFox]

I have a similar unit from Marconi:  the two oscillators can be used independently, but switching the output of each to "rear" connects them to the central combiner/meter/attenuator unit.

[Mike99]

I worked for Racal for 30 years, and yes we used a lot of tantalum beads. I've had to replace them in every piece of Racal equipment I currently own.

I'm not familiar with your generator but I know Racal-Dana rebadged equipment because I recently repaired one of their oscilloscopes and it was made by VuScan.

Mike

[lowimpedance]

if only I had the schematics and parts list.  I don't want to try and reverse engineer it first.

I have attached a scan of the oscillator and buffer amplifier schematic for the RACAL two tone generator.
Pretty sure its relevant to your version !.

 I worked at RACAL in the early eighties here and had used those generators, and must have thought it would be nice to have a copy of the oscillator cct  .
Copying was tedious then so must have decided I didn't need the rest of the schematics I guess    .

I have no idea what happened to all the gear and extensive library at RACAL when they shut up shop here  . I did however pick up on ebay a number of years ago a RACAL 4003 DMM which is a re badged Keithley 177, this unit was actually used within RACAL,  and quite possibly one I had used while working there, (possibly )
So yeah re badging was regular practice 

[wn1fju]

Thanks for the schematic, it is a big help.  Of course, the component values will be slightly different in my unit because I have the 9083N, not the 9083.  The two oscillators in the "N" variant are both to 20 kHz, whereas the standard unit has one channel to 10 kHz and the other to 110 kHz.  But I assume it's only a simple change of a few R and/or C values.  I can't find a whole lot of information online about the 9083 and even less about the 9083N.


 

[factory]

Racal also rebadged some TTI power supplies, Scopex & Hitachi oscilloscopes, a Data Tech DMM and I have a Racal branded AIM Databridge LCR bridge.

David