Updating older hf amplifier

18-Jun-2014 21:41

So think about these potential problems at twice before investing in such an equipement.

I took the example of a k W class amplifier as it is widespread in the ham community among hams who have the chance to be allowed to use so high powers.

But I have never said either that an amplifier might replace a defective antenna. Do never use a high power to compense the poor performances of an antenna.

This is indeed the best way to create QRM or get serious troubles if your installation (cabling system, SWR-meter, power supply, etc) is unable to sustain such power, thus high currents. Improve first your antenna system in reducing the ground effect, use a low loss coaxial (RG-213, Belden RF-9913, Aircom, etc), try to get an excellent VSWR on the line, as much features that, once optimized, will increase the efficiency of your installation. If your transceiver last stage is badly matching your amplifier input specifications, you have all chance to burn your P. The Kenwood TL-922 amplifier for example must be driven with an input power ranging from 80 to 120 W PEP, no less no more.

These few examples of behaviours do not respect either the ham spirit nor your health and are not very useful.

And all the more that an amplifier is often expensive and bulky, and requires some basic knowledges of the subject if you want to respect the other hams working on the air as well as the regulation.

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All high-end k W amplifiers display big, strong and rugged accessories, large coils, big capacitors, heavy toroidal transformers, big choke, for short all is big and seems to offer an excellent quality.

With these positive and negative experiences, nowadays there are two ways to select a tube amplifier, for short the expensive and the cheap one; in other words selecting high or low quality tubes. For decades quality tubes were manufactured by Eimac, RCA or Westinghouse among others U. even ten times cheaper were manufactured in Russia and eastern states. So if you have the choice and some money left, you can purchase an expensive 8877 tube and alike made by Eimac, which production is ensured for some decades. The positive side is that you can buy several of these reliable tubes together with your amplifier at the time of purchase.