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eHam Forums => Elmers => Topic started by: W7PTT on May 03, 2006, 08:52:35 PM



Title: Kenwood TS-530SP and driving an amp
Post by: W7PTT on May 03, 2006, 08:52:35 PM
Hello all

I was just using my friends Kenwood TS530SP with my Alpha 99.  It appears that when you run this rig in SSB phone that you can't cut the power down (below about 68 watts).  For example, I have an Alpha 99, and I usually drive it with about 20 or 25 watts (gives me about 600 watts out of the amp).  When I adjusted the Kenwood, I noticed that when I was speaking into the mike (even with very little mic gain)the output would go from about 15 watts, then jump up to about 68 watts.  This is not a good thing if you want to only drive the amp with 20 or 25 watts. Is this typical of the older kenwood rigs, or does the rig have a problem?    Looking to buy one, but not if I can't make the rig only run about 20 or 25 watts into the amp.  Is it that older amplifiers took more drive so that is why 68 watts was not a problem back then?

73

Bill
W7PTT


Title: Kenwood TS-530SP and driving an amp
Post by: N3BIF on May 03, 2006, 09:09:33 PM
"  Is this typical of the older kenwood rigs..."

          Yes!


Title: Kenwood TS-530SP and driving an amp
Post by: WB2WIK on May 04, 2006, 08:31:05 AM
Connect the ALC line and use the amplifier to adjust the power output of the Kenwood.

Unfortunately, some Alphas have poor ALC and I've even seen them recommend to *not* use the ALC, which is pretty whacky, since a good ALC system is great.

The TS-530SP does not have a "power output" control of any kind that works on SSB.  It can adjust down to just a few Watts output on CW, though -- just not on SSB.  Turning the mike gain down is *not* a good way to control output power on "phone."  In fact, it's a terrible idea, with any kind of rig.

One easy thing to do is to use a 6 dB 50W attenuator between the rig and the amplifier, and bypass the attenuator on receive (so it's only "in line" on transmit).  That's not difficult to accomplish, and will allow the amp to coast with reduced drive and absolute assurance you can't overdrive it.

WB2WIK/6


Title: Kenwood TS-530SP and driving an amp
Post by: RobertKoernerExAE7G on May 04, 2006, 12:49:37 PM
Why replace the rig that works FB with you Alpha, with one that does not?


Title: Kenwood TS-530SP and driving an amp
Post by: W8JI on May 05, 2006, 02:59:05 AM
To have the cleanest signal, we should always run radios at sligtly less than rated power.

NOT way less than rated power, not anything over rated power.

Using ALC is NOT a good way to reduce power. It is like closing the barn door after the horse is out. You will never find an ALC system that is fast enough to not distort the leading edges. The reason is the response time has to be significantly faster than the rising edge of the waveform, and that just isn't going to happen.

There are very few radios that work OK at reduced power, and I haven't seen on yet that is as clean at 1/4 power as it is at 1/2 or 3/4 power. (Measuring true PEP.)

The best suggestion if you really want to reduce power is to build a 6dB pad and run the radio at slightly less than full PEP power.

What you are experiencing is why I don't like and don't use "low drive" amplifiers. The amplifier should be matched to the rig in drive requirements. An attenuator is a good way to do that.

73 Tom