[AMRadio] PRC vacuum tubes

John Lyles jtml at losalamos.com
Tue Oct 11 02:08:45 EDT 2005

I had a very recent experience buying a "house brand" 3-500ZG, and an Amperex 3-500Z, from a reputable national RF parts dealer. The 500ZG was stamped with their name, and had PRC on it (Peoples Republic of China). I noted that the envelope was slightly different in length and diameter, but not by much. But the annoying thing was that the anode with grid/filament basket inside, were not concentric with each other. In other words, the spacing from one side of the anode cylinder was closer to the grid than on the opposing side! This is not an old Chinese tube, but a 2004 date code product I believe. With such a misalignment, the electron optics via the grid would be suboptimal on one side(with anode to grid space too close) and also on the other (too far). The net (average) performance of such a tube would most likely pass test parameters, as the increased capacitance on one side would balance against the decrease on the other. Likewise for the mu factor. However, this sort of sloppy
build does not lend confidence in that product. If the tube were run hard near its dissipation limits, grid warpage may occur as the one side may run hotter than other. Such a failure mode is usually catastrophic in bigger tubes that I have autopsied, where the warped grid causes a hot spot on the anode which in turn caused additional warpage, until the tube fails. The Amperex tube, on the other hand, was made in their Covimag plant in France, and was aligned as a new tube would be expected. It clearly had a better 'look' to it. I plan to run both tubes in a particular socket at work soon, to compare them for an application that we are replacing 3-400Z triodes in. 

I once found similar variations in high power Bipolar power transistors for 880 MHz, 150 watt PEP parts. We found that the 'second source' from ST had bond wires which were not parallel, they were bonded at a diagonal as if done by a crooked machine or by hand, and had different lengths, with minute changes. We opened the Motorola MRF899 at the time and it was visually much more symmetric and uniformly built. We selected that source only for our 3 kW 800 MHz amplifier that we developed. We were unable to get the ST part to play in our amp without significant retuning. 


> Date: Sat, 8 Oct 2005 08:36:32 -0500
> From: "Ed Swynar" <gswynar at durham.net>
> Subject: [AMRadio] Chinese TOOBS...Epilogue
> To: <glowbugs-list at piobaire.mines.uidaho.edu>,	"Welcome to the Novice
> 	Rigs List!" <novice-rigs at mailman.qth.net>,	"Discussion of AM Radio"
> 	<amradio at mailman.qth.net>,	<boatanchors at mailman.qth.net>
> Many thanks to all who took the time to share their experiences with Chinese hollow-state devices...much appreciated.
> The synopsis seems to be that the very early offerings from "...Beijing Inc." were LESS than ideal --- however, the jury is still out re. the durability / performance of their latest offerings. One note of interest: the current Chinese 211 seems to behave every bit as well as anything vintage from the U.S.A., per comments from one user...
> I guess it's all just a matter of time...I recall as kids we used to laugh at anything that was marked "Made In Japan" --- and look at what's happened since then...
> Thanks again to all, & very
> ~73!~ Eddy VE3CUI - VE3XZ

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