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Author Topic: SB-200 PROBLEM  (Read 3855 times)
KB0UGS
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Posts: 10




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« on: May 17, 2011, 10:02:39 AM »

sb-200 recieve problem..when amp is in-line but in the off position recieve audio is good, as soon as i turn the amp on recieve audio drops way down.. i have clean contacts in relay with contact cleaner and paper...have noticed that moving the tune control audio changes but still way way down....any help would be appreciated.. thanks and 73
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W9PMZ
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« Reply #1 on: May 17, 2011, 10:12:19 AM »

what is the transceiver you are connected to?

you may have connected a low voltage tranceiver to the hv sb200 and welded the transceiver in the xmt position; or you have a short in the relay cable.

73,

carl - w9pmz
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KB0UGS
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Posts: 10




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« Reply #2 on: May 17, 2011, 10:22:01 AM »

station is ic-706mkiig with new relay buffer and cable to sb-200...i can heat the amp relay key when i turn it on an in the plate position it reads 80 mils without the radio keyed..hv is 2400 volts..the transiever is keying properly.. it has indicator for transmitt and recieve...
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KA5N
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« Reply #3 on: May 17, 2011, 10:29:03 AM »

As the previous poster hinted, the problem is probably somewhere in the relay circuit.  The relay circuit is unpowered unless the amp is on.  So first unplug the cable to the KEY input of the amp.
If problem goes away then look for a short or transceiver problem.  If trouble persists with cable unplugged then there is a short (or partial short) somewhere in the relay circuit.  Correct action of the relay depends on all the resistors being the correct value so check them.
Also the armature on the relay could be faulty in some manner, such as a bad spring or warped contacts.  
I hope you realize that the SB200 RX/TX relay circuit is powered by -125 VDC and most modern transceivers will not handle this voltage level or negative voltage.  So either use the internal soft key mod sold by Harbach Electronics or one of the inline buffers sold by Ameritron or the Heath Store (not sure of the exact name).
I hope you haven't damaged your transceiver.
Good luck
Allen
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KB0UGS
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Posts: 10




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« Reply #4 on: May 17, 2011, 10:33:48 AM »

i have a new amp relay buffer and cable in-line...i did take some voltage mesurements of the phono cable that hooks to the amp for keying and i did notice voltage is 135.8 volts neg..
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AH6RR
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Posts: 803




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« Reply #5 on: May 17, 2011, 11:10:54 AM »

Sounds like the keying buffer is wired wrong or there is a problem in the amp since you said when you turn on the amp it shows 80mil of current that means the amp is keyed. Try to unplug the Relay plug at the amp and turn it on if it is still shows 80mils of Plate current if it does not then check the Relay Buffer wiring if it still shows 80mils then you have a bad tube in the amp.

Roland AH6RR
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KB0UGS
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« Reply #6 on: May 17, 2011, 11:46:28 AM »

i unplugged the relay buffer and it does not show any plate voltage now...i can manually key the amp by shorting the phono cable that go to the amp relay...HUMMMMMMM...
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AH6RR
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Posts: 803




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« Reply #7 on: May 17, 2011, 01:20:18 PM »

Most of the relay buffer interfaces have jumper settings inside and must be set correctly for your radio for it to work properly. So find the manual for the buffer relay and set the jumpers for your radio and you should be ready to go.
Roland AH6RR
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K7KBN
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« Reply #8 on: May 17, 2011, 02:33:34 PM »

i unplugged the relay buffer and it does not show any plate voltage now...i can manually key the amp by shorting the phono cable that go to the amp relay...HUMMMMMMM...

Is that Plate VOLTAGE or Plate CURRENT?
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73
Pat K7KBN
CWO4 USNR Ret.
KB0UGS
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Posts: 10




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« Reply #9 on: May 17, 2011, 02:37:14 PM »

my mistake... plate current..
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W4ETN
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Posts: 8




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« Reply #10 on: May 18, 2011, 07:30:46 AM »

The SB200 amps change over circuits switch high voltage that the IC706MKIIG can not handle.  I built a relay switching unit that converts the IC706 to drive a relay that keys the SB200.  I can send you the schematic if you like.  My contact info is on QRZ.com
Bob
W4ETN
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W4TMC
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« Reply #11 on: May 21, 2011, 05:36:01 PM »

I had this problem several years ago.  If you have the stock relay it has to be the spring on the relay frame.  I stretched out the spring a small amount and used it for several more years.  Later, I put in new relay from Harbach.

73

Mike W4TMC
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KD8GKR
Member

Posts: 47




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« Reply #12 on: May 22, 2011, 06:40:27 AM »

what kind of relay buffer are you using? I used one from ham gadgets a while back with a SB-200 and had reverse the leads on one end of the cable from the buffer to the amp to fix the same problem you are having. Not sure if it was an assembly problem with the buffer but once the cable was changed problem never re-appeared.
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N5UD
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Posts: 827




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« Reply #13 on: May 25, 2011, 05:38:03 AM »

Since you say the SB-200 plate (current) meter is showing 80 mils, it is keyed. Unplug the amplifier keying interface. Verify if this clears the keyed state of the SB-200. If it does, trouble shoot make settings to your keying interface.

My local buddy bought one ( amp key interface) a few months ago. It worked for few days then broke. So far as I know, he is still using just the exciter at 100 W.

73 Tony N5UD
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K8AXW
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Posts: 4004




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« Reply #14 on: May 25, 2011, 09:05:22 AM »

Is the keying interface controlled by diodes or transistors?  Is it possible the interface is for a different polarity amplifier?
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