[TenTec] Solid State Amplifiers

[Ken Brown <ken.d.brown@verizon.net>]

Hi All,

My experience with solid state amplifiers on HF is limited to one 
amplifier, the SCG SG-500. I bought this amplifier because I was doing 
160 meter contest operations from locations that had no commercial grid 
power, and I wanted to be able to run significantly more than 100 watts. 
At the time I was using a Kenwood TS-440 transceiver, and I had already 
converted a Heath SB-201 to operate on 160 meters. The TS-440 has pretty 
good QSK and I got used to having QSK. So when I started using the 
SB-201, which is not a QSK amplifier, I put together some circuitry to 
switch the receive signal around the amplifier and directly to a RX only 
antenna jack that I installed on the TS-440. When I got the SG-500, this 
same setup worked to give me QSK functionality, with an amplifier that 
is not a QSK amplifier.
I never had a problem with the SG-500. It performed as advertised. It 
has numerous protection features which prevented me from ever blowing it 
up, even though I did occasionally make a few blunders that might have 
blown it up without the protection.

One of the protection features that it has is an internal attenuator on 
the input, which automatically switches in if you give it too much 
drive. With the TS-440 turning down the CAR (RF output) control resulted 
in a funny, soft leading edge, CW keying envelope. I might have been 
able to make some tweaks to the ALC on the TS-440 to make it sound right 
at 50 watts output, and then I probably would not be able to use it at 
100 watts anymore. So I built a power attenuator. A bunch of 2 watt 
carbon composition resistors in a T configuration made about 2.5 dB 
attenuation. Putting it in a one quart paint can full of mineral oil 
made it handle the power nicely.

The other thing that was a lot of work, was finding and carrying a power 
supply system that will provide the 100 amperes peak that the SG-500 
needs. I used many different combinations of multiple paralleled power 
supplies and batteries. I always made it work. It was always a hassle 
though.

The SG-500 is not the perfect amplifer for me, however I must say that 
it is an excellent product, which does what the manufacturer says it 
will do. I still have it, because someday I plan on using it for a 
mobile setup. I am really curious to find out how susceptable to RF some 
of the high power car audio systems on the streets are.

Now I have an Omni VI and a Titan. The QSK is much better, and it puts 
out the legal limit. And the setup is much less complicated than the 
kludge that I had put together to make the SG-500 work the way I wanted 
it to.

Ken N6KB


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