Before Hewlett-Packard invented the negative-resistance-stabilized, Wien Bridge oscillator-and patented it, kicking the ass of overrated GenRad and others-generating a low distortion sine wave at low (audio) frequencies that was stable and level was quite a problem. Before this, the most common method was the heterodyne oscillator, which used two RF oscillators, one a fixed frequency and one almost fixed which could be "swung" just enough to produce a beat frequency that was variable from zero to as high as one wanted, as long as it was a relatively small multiple of the working oscillator frequencies. Many companies made them, including Bruel and Kjaer, GR, and even GE and Motorola. When the HP patents finally pooped out the heterodyne frequency oscillator became a thing of the past. By that time solid state was firmly established and the basic building block linear ICs had started coming out.
The phone company of course had their own source. Western Electric came up with the early dry cell all-triode 11A heterodyne oscillator in a beautiful wooden case, and followed with the metal case rackmountable or portable 19C oscillator. It had some unusual features such as it was an AC-DC set, like the old AA5 radios. This construction is extremely rare in test equipment because of the shock danger that would normally accrue. But the 19C was fully transformer coupled, using many of the then-readily-available WE coupling "repeat coils", and was isolated in its case and at its output terminals from line voltage.
At one time the WE 19C was a hamfest no-wantum, an undesireable rat that got hauled from hamfest to hamfest until the hamfestgoer went /SK and it went to the landfill. Bunches were made and were surplused out or "destroyed via station wagon" when the 4A ESS decided its lack of stability made it unsuitable for test purposes. It was a heavy beast and phone crews came to hate them over time. It was referred to, not affectionately, as "the woo-woo" because it would whine audibly and its audible whine would change in pitch with any serious variation in line voltage.
Anyone carefully watching eBay over the last couple of years would have seen a different story. Whereas classic HP Wien bridge audio generators often sell for less than the cost of shipping, the 19C and its relatives-variants built for GTE, Northern Electric, or NTT-are now bringing anywhere from four to eight hundred dollars on eBay.
Two things which were unusual immediately became obvious. Invariably, the buyers were located in Asia, usually South Korea, Japan, Taiwan or mainland China. Also, the price seemed unrelated to the condition of the set. This was an unusual phenomenon because Oriental buyers of old tube electronics are usually obsessed with appearance and originality.
I became convinced that the units were being bought for some reason besides use, and I suspected they were parting them out for the numerous audio transformers in them. Recently, I called a couple of the known sharks, Oriental and American, for old tube gear and after some hemming and hawing they confirmed my suspicions. They remove the transformers and throw the rest out in the trash.
Of course, the transformers are not very good for the purpose to which they are put, but this makes no difference to the buyers. They are genuine Restrum Erectric, that is to say Western Electric, and to a people who eat bear gallbladders and rhinosceros horn to make their notoriously undersized male members stand up, the facts aren't too relevant.
I believe the time is now to put an export tax on all old electronics from the United States. This would help environmentally by forcing the US to recycle its own commodity electronic trash and to make the little nippers help offset the federal debt they have helped to cause. Your thoughts on this issue would be welcome.