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Source: Innes Corporation
Author: John S. Innes
There are two reasons for having transmitting tubes rebuilt, rather than replacing them with new ones – price and performance.
Rebuilding services are able to re-use most parts of a tube that is worn out but undamaged. They rebuild the tube with a completely new filament assembly, which gives it a service life at least as great as a newly manufactured tube. This saves much of the manufacturing cost of a complete tube, and offers the user an economical alternative.
The number of transmitting tube manufacturers making a particular tube type is quite small, and without rebuilding there would not be much competition in the business. The tube manufacturers would be able to charge prices well above the levels now set by the marketplace. The market stays in balance, as the stock of tubes available for rebuilding is limited to the number taken out of service at the end of their useful life, less a few that are damaged due to fault conditions or abuse in service. The limited supply of used tubes means that there is no surplus of rebuilt tubes to offer for sale, and is the rebuilding service, rather than the rebuilt tube, that is sold.
Apart from the cost saving, there is good reason for having a used tube rebuilt. The filament of a transmitting tube can be built in several ways. The simplest and most common way is to string filament wires parallel to each other, under spring tension. A better alternative, used wherever possible by the tube rebuilder, is to construct the filament in the form of a lattice or mesh, which provides a greater filament area, giving higher peak emission capability and longer life. It is also a more rigid structure, allowing closer dimensional tolerances to be held giving more stable operation. In VHF and UHF service, the mesh filament approximates a cylinder, giving lower inductance and a more uniform RF voltage over the entire surface. The improvement in performance can be substantial.
There are some low cost suppliers, generally in low labour cost countries, but as they may not have access to the very high purity metals needed, tube quality is not guaranteed.
Innes Corporation sales new transmitting tubes and offers the service to rebuilt your old tubes through Freeland Products, Inc.. To find out more contact our friendly sales department at sales@innes.com.au .
For tips on better tube performance by our friends at Freeland click here.
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