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Author Topic: Keying SB200 amp with Icom 720a  (Read 1112 times)
KB5GC
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Posts: 6




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« on: April 25, 2005, 05:02:12 PM »

I'm looking at purchasing a Heathkit SB200 amp for my Icom 720A (vintage 1981).  The icom is one of the early solid state rigs.  Will I need an interface relay to key the amp?  If so who is a good supplier?

thanks vy much!

-Chuck
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K0BG
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« Reply #1 on: April 25, 2005, 06:55:15 PM »

The MFJ ARB-704 sells for $50 list and is just what you need.

Alan, KØBG
www.k0bg.com
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NI0C
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« Reply #2 on: April 26, 2005, 08:08:24 AM »

The "AmpKeyer" is a little cheaper than the Ameritron unit.  Check out reviews of both under eHam Product Reviews, "Interfaces, radio-computer, radio-amplifier."
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KB5GC
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« Reply #3 on: April 26, 2005, 08:38:05 AM »

Right now, I've been keying a Dentron GLA-1000 directly with this rig.  Do you 'spose I'm in major danger of frying something in the rig?
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NI0C
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« Reply #4 on: April 26, 2005, 09:15:03 AM »

In order to answer your question, you need two pieces of information: the open-circuit voltage presented to your transceiver by the Dentron relay, and the current that your transceiver will sink when the Dentron relay is closed.  (You can determine both of these quite easily by measuring with a multi-meter or from the Dentron manual).  These numbers should be compared to the limits of the transceiver keying relay or transistor to determine if you are operating safely.

73,
Chuck  NI0C
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K0BG
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« Reply #5 on: April 26, 2005, 11:40:27 AM »

The 720 uses a very small relay hardly bigger than your little finger. I suspect you're at the limit. No matter which interface you buy, you'd best.

Alan, KØBG
www.k0bg.com
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W9GB
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Posts: 2656




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« Reply #6 on: April 26, 2005, 04:41:43 PM »

The AmpKeyer and MFJ are solutions, and the AmpKeyer provides you with a stand-by feature desired by some amateurs.  The other choice is the Harbach Soft-Key mod for the SB-200.  Jeff is accepting orders on May 1st and will be at Dayton.
http://www.harbachelectronics.com/

SB-200 SoftKey instructions and schematic
http://www.harbachelectronics.com/reference/harpg8.htm

w9gb
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W9GB
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« Reply #7 on: April 26, 2005, 04:48:09 PM »

Chuck -

Since you are likely going to purchase an SB-200, you might wish to read Bob Norgard's SB-200 Rebuild Notes (with photos)
http://home.gci.net/~rnorgard/ampnotes.html

Since these amplifiers are at least 20 years old, some component replacements are "automatics" for trouble free operation.  Bob covers most of these, but the changeout of the HV electrolytics, meter protetion and the soft-key mod should be considered the minimum "refresh".  572-B tube replacement will vary greatly depending upon the condition of the tubes within the SB-200.

w9gb
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KB5GC
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« Reply #8 on: April 26, 2005, 05:53:52 PM »

Thanks for all the info!

I ended up finding this on eBay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5768223602

Probably $35 is getting to be too much for a used one, however he lives nearby, so I'm hoping to save a couple of bucks on shipping.

-Chuck
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W9GB
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« Reply #9 on: April 29, 2005, 10:39:06 AM »

Chuck -

I actually have the schematic / manual (Adobe Acrobat) for the Yaesu FRB-757 box (somewhere). You will need to build some cables to interconenct with the IC-720 and provide a source of power for the relay (13.8 VDC as I remember). IF you need the small manual / schematic drop me an e-mail callsign at arrl.net .. and I will "dig it up"

Greg
w9gb
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KB5GC
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« Reply #10 on: April 29, 2005, 10:43:31 AM »

Thanks much Greg!! I did happen to find a PDF of this online, and wired it to my 12v ps.

Unfortunately, this morning I managed to fry the final PA stage of my Icom.  It is toast.  I don't think it had anything to do with a relay, but something to do with a bad (read cheap) antenna switch.  So I put what's left of the Icom up on the Classified boards.  :-(

73,

Chuck
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KC8VUK
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« Reply #11 on: February 16, 2006, 07:09:14 AM »

 I just bought a sb-200, it came with the AMPKEYER, and I got the right cables fron radio shack, and hooked them up, and the ampkeyer, works, fine!!! No internal wiring needed, look up, ampkeyer on the net, and buy one, instructions come with it!!
  73'  Billie kc8vuk
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