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Author Topic: Heath sb 200/ Kenwood 950  (Read 1904 times)
WB8JBG
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« on: August 02, 2009, 11:22:43 AM »

I would like to connect my heath sb 200 to my Kenwood 950, I have read all the topics under amps, and am a little confused. Do I have to install a "Harbach or Soft start" in order to use the amp with my Kenwood?
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W1QJ
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« Reply #1 on: August 02, 2009, 12:53:02 PM »

If I am  not mistaken the Kenwood matching amp to the 950 was the TL-922.  The TL-922 amp had a 120vdc relay just like the Sb-200 does.  Since both amps have the same relay voltage and the 950 was compatible with the 922 with no needed mods, I would assume that the 950 would also handle the Sb-200 as well.  Now i am assuming you mean you have a TS-950 and not some newer radio with a 950 number.  Does anyone else agree?  73 lou
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WB8JBG
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« Reply #2 on: August 02, 2009, 01:43:42 PM »

Yes I do have the TS 950
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K4DPK
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« Reply #3 on: August 02, 2009, 06:11:09 PM »

I hate to butt in here, but the safest thing to do would be to get a relay interface to go between the keying line of the radio and the amplifiers' transmit relay.

This has absolutely nothing to do with the "soft start" mod for the amp.  That is something to protect the power supply components in the amplifier.

The keying interface is to protect the transceiver from being harmed by the high voltage that is present on the keying relay circuit in the amplifier.

Phil C. Sr.
k4dpk
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K4TLJ
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« Reply #4 on: August 03, 2009, 05:52:38 AM »

Perhaps this little circuit which can be built cheaply if you don't mind a bit of soldering...
http://home.comcast.net/%7Esuptjud/Heath_SB_200KeyingCircuit.jpg
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K0XU
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« Reply #5 on: August 03, 2009, 08:26:07 AM »

"I hate to butt in here, but the safest thing to do would be to get a relay interface to go between the keying line of the radio and the amplifiers' transmit relay."

Most Kenwood rigs (up through my 570 anyway) use a relay to key the amp. Relay is rated for 250 volts 0.5 amp. Will easily handle the relay keying voltage, what safety is gained by adding something else to go wrong? Works great with my old HB 4-1000A.

Jim K0XU
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K4DPK
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« Reply #6 on: August 03, 2009, 10:25:29 AM »

K0XU,

Jim.  Take a look at the SB-200 circuit.  The relay line is tied to the tube grids.  If either of the tubes flash over, you have a chance of an instantaneous 1800-2000 volts on the keying line.

Phil C. Sr.
k4dpk
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W3LK
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« Reply #7 on: August 03, 2009, 10:53:49 AM »

<< Most Kenwood rigs (up through my 570 anyway) use a relay to key the amp. Relay is rated for 250 volts 0.5 amp. Will easily handle the relay keying voltage, what safety is gained by adding something else to go wrong? Works great with my old HB 4-1000A. >>

Because if there is an amp malfunction, the cost of replacing a blown interface is FAR LESS that the cost of replacing the 570's keying relay.

73,

Lon - W3LK
Naugatuck, Connecticut
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K4TLJ
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« Reply #8 on: August 03, 2009, 07:46:40 PM »

My little keying circuit linked in my previous post can be built for $2.00 or less. The amp then can be used with any transmitter.
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WB8JBG
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« Reply #9 on: August 04, 2009, 09:38:35 AM »

Maybe this info will help, I have the 950 connected to a Henry @K classic at present and it works fine. Wouldn'y the Henry and the Heathkit basicly be the same in the method used to key the amp?
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K4DPK
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« Reply #10 on: August 04, 2009, 10:09:22 AM »

The 2kClassic has a 12 volt relay system, uses 3-500z tubes in grounded grid and keys the cathode circuit.

The SB-200 uses 572B tubes, with the grids grounded for RF but not for DC.  The Relay voltage is negative at more than 100 volts, and that negative voltage is used to bias the tubes to cut-off when in standby.

The fact that the grids are above ground, and the keying line is tied to the grids affords the opportunity for the keying line to carry plate voltage (2kv) into the TS950 if the tubes flash over, which they occasionally do.

Incidentally, this same thing can happen with 3-500z amplifiers, but with the biasing and keying in the cathode circuit, all that happens is loss of the zener diode.

While I'm on the subject, one way to keep from losing the zener in such amps is to put an NE-2 bulb across it.  When a flash occurs, the neon ignites and protects the diode.

Phil C. Sr.
k4dpk
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KC6ZBE
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« Reply #11 on: August 11, 2009, 01:09:32 PM »

Im using a Kenwood TS-440 with the SB-200...Im using a little box called an "Ampkeyer" that ran about $40 and has the protection for the keydown currents. The best part about the Ampkeyer is that it has a standby switch on it that the SB200 doesnt have.

Harbach makes the "softkey" module for the SB200 that installs internaly. The Ampkeyer does the same thing but is external. I mainly got it for the "standby" feature.
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