Wiltron 6659A Programmable Sweep Generator: 10 MHz to 26.5 GHz, in a single sweep…

This instrument just needed a few adjustments, still, very interesting to look at.
It is of a very classical design – 4 YIG oscillators (2-8, 8-12, 12-18, 18-26.5 GHz), a coupler, a detector, and all the driver and ALC circuitry to make this work.
There is also a Wiltron-brand downconverter that provides the 10 MHz to 2 GHz output, by conversion of a 4610-6600 MHz input, with a 4600 MHz LO.

The YIGs are all of best quality, Avantek parts.

The coupler, for the ALC loop, a Krytar ultra-broadband part, with a biased detector.

wiltron 6659a

6659a alc detector

wiltron 6659a yig assy

wiltron 6659a front

The generator provides ample power, 10 dBm or more, over most of the bands; about +6 dBm, at above 18 GHz – and, around 23 GHz, there is a dip in the power curve (see scope screen, showing the ALC/power signal vs. horizontal sweep). Checked the bias (was set at a constant +11 V) – changing it, and going up to +15 V, no change. Also checked the power directly at the YIG output – still, the dip. So it seems, nothing we can do about it, but for most practical purposes, about 0 dBm will be plenty, at any frequency.

wiltron 6659a power measurement

After some more alingments, the frequencies and bands are spot-on (no need to re-programm the linearizer EPROMs – all YIGs are still tracking perfectly fine), some some cleaning, using 50% isopropyl alcohol – done.

The only thing left to be done – a back-up of the 2716 EPROMs that still hold the firmware, after about 30 years.

4 thoughts on “Wiltron 6659A Programmable Sweep Generator: 10 MHz to 26.5 GHz, in a single sweep…”

  1. Hi, Do you happen to know the frequency of a Wiltron 1005-c-22086 oscillator? I have a store on eBay besttestus.
    Thanks I will definetly return the favor, as I have thousands of parts and manuals yet to list.

    1. Hi Bill, I don’t have a datasheet but pretty sure it is a 2-8 GHz YIG oscillator. Probably it will go a bit below and above the range.

  2. Hi Simon,

    I’ve got one of these (same model, 6659A) that worked quite well until it started spitting out error codes 07 and 08 last week. According to the self-test error codes (Operation and Maintenance Manual, Table 3-3), they have to do with ROM U9, and/or RAMs U11, U12, U37, and U38 on hte Microprocessor board, A12. Now, Table 6-22 lists U9 as “Not Used” (how can it have gone bad then?), but the RAMs do have a part number. My PDF of the manual doesn’t have enough of Section 7 to troubleshoot the microprocessor board problems. It’d be a shame to have this thing brought to its knees because I can’t figure out if replacements are necessary, or if they can be found. I’m trying to use it as test equipment for non-commercial (amateur radio astronomy) purposes.

    Do you have a full repair manual?

    Evan M.

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