Seductive serendipity / Verleidende serendipiteit

October 28th, 2007

Carlos Vamos and Lindsey Buckland

Yesterday I went shopping in my city and immediately heard nice sounds from the main street. A -by Hilversum standards- large crowd gathered around two guys playing astonishingly good, nice and ambient music. People tapping with their feet, children quietly listening, mothers and fathers laughing. These two guys were performing, selling a lot of their CD’s and earning good money!!

Playing guitar myself, I was impressed by the completeness of their sound and espcially their techniques. I bought a CD from them and found out that the guitarist Carlos Vamos really is a virtuoso!

A promotion video of them can be found at YouTube.

October 5th, 2007 upgraded

This week I upgraded my firewall and, inherently, this site The old site was running on WordPress 2.0 and an AMD K6-2/300 with 96 MB memory and 4 GB harddisk. I bought a surplus Compaq Evo D500 – P4 1.7 GHz with 512 MB memory and 20 GB harddisk from for a nice price and upgraded to WordPress 2.3.
Below you see a picture of this machine.

October 5th, 2007

Second AM6154 delivers a stable 500W output with 2.2W drive

Jurgen PE1LWT (see right, click on picture to enlarge), bought a second AM6154 for me in Friedrichshaven last June. It looked like a virgin and the first challenge was to power it up. The first result was that we did not experience a big bang with corresponding flashes, also not after powering up the 2.4 kV plate voltage. Because this amplifier was originally designed for aeronautical AM (amplitude modulation), the amplifier was immediately set in ‘idle’ mode.
While approaching the amplifier, we saw that the plate current was ‘ticking’ as well as the screen voltage. We first thought it was the electrolytic capacitor in the screen power supply. It turned out that the screen (G2) glass overvoltage protector was arcing. My philosophy is, remove as much protective devices as possible because they cause and create more damage than they protect!
So we did.The amplifier was left into idle mode during a coffee break and my cat jumped on it, almost got electrocuted because his tail was hanging in the high voltage power supply. Besides the activity of the cat, we did not hear strange noises, nor could we smell strange odours from the amplifier.

So, the next step would be to apply some drive. We applied a little drive to the amplifier, tuned it and soon measured 100W output.

After tweaking and tuning we reached 300W with almost 12W (!) of drive (see right, click on picture to enlarge). We expected a bit more output, but, we left the amplifier ‘key down’ at 300W during the evening. This resulted in a VERY HOT Spinner dummyload. But also it demonstrated that the amplifier was stable with this output and… it is a quick way to recondition a tube!

My other amplifier, with a GS-36B inserted, delivers almost 3 dB of output more. So, it was time to modify the amplifier and make it ‘contest ready’.

The input circuit was completely modified according to the FYM-tetrode match. Perhaps for reasons of (in)stability, but I cannot understand why the standard input circuit of the AM6154 is designed so inefficiently. After this and some other modifications, the amplifier delivered a stable 500W with 2.2W of drive power. A good backup amplifier for the contest!!