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   Home   Help Search  
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Author Topic: Kenwood TS-850S Amp Buffer  (Read 1149 times)
W9IQ
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Posts: 3553




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« Reply #30 on: September 13, 2019, 06:55:01 PM »

Bill,

For that SSR to work, you will need a minimum load current of 20 mA. The relay circuit you added to your linear will not be sufficient. You will need to put an additional load on the output (e.g. a resistor, LED or lamp).

Also make certain you order the DC version of the SSR (MPDC...).

- Glenn W9IQ

« Last Edit: September 13, 2019, 07:07:02 PM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W9IQ
Member

Posts: 3553




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« Reply #31 on: September 13, 2019, 07:52:47 PM »

I would also suggest that what fried your board is the the 850 12 volt on transmit pin sources 12 volts. You modified keying circuit in the amp also sources 13+ volts.

If you wish to use this type of interconnect, simply remove the diode in your linear switching circuit that is powering the relay and remove the electrolytic filter cap. This will make your amp a current sink for the 850 voltage source.

No matter which way you go, don't forget the flyback diode on the amp's switching relay.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KO4NR
Member

Posts: 221




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« Reply #32 on: September 13, 2019, 07:59:22 PM »

Bill,

For that SSR to work, you will need a minimum load current of 20 mA. The relay circuit you added to your linear will not be sufficient. You will need to put an additional load on the output (e.g. a resistor, LED or lamp).

Also make certain you order the DC version of the SSR (MPDC...).

- Glenn W9IQ


I'm using two PCB relays in the amp for T/R.  I've had them in there for about 14 years now.
https://www.azettler.com/pdfs/az755.pdf
At 12vdc and a coil resistance of 275 ohms they should draw about 43ma each.

73,
Bill KO4NR
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W9IQ
Member

Posts: 3553




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« Reply #33 on: September 13, 2019, 08:01:50 PM »

Yes, that should do it then.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KO4NR
Member

Posts: 221




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« Reply #34 on: September 13, 2019, 08:12:29 PM »

Yes, that should do it then.

- Glenn W9IQ
Appreciate your well thought out feedback. All the information shared in this thread will be a big help to others in the same boat.
73,
Bill KO4NR
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KO4NR
Member

Posts: 221




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« Reply #35 on: September 13, 2019, 08:30:01 PM »

The burned spot on your board is because of Q43. Q43 supplies 12VDC to pin 7 on the remote connector and is 10ma MAX current draw. It is not part of the amp keying circuit. You amp should be connected to Pin 2 (common) and Pin 4 (switched). Neither is connected to ground. When activated the 2 pins close using a relay with contacts rated at 2A to key the amp.

Most likely. You were using Pin 7 to key an external relay to key the amp and that relay draws ~100ma, 10 times what Pin 7 is rated for and it finally burned up. Hook up the amp correctly.

His connections and schematic are correct -- and he indicated it was working correctly for 14 years.  Pin 7 sources current limited +12V as you describe but does not directly connect to the amp's relay.  Pin 7 provides +12V any time the TS-850's TX is engaged and its connected to his buffer circuit.  His schematic shows pin 7 connected to a pair of 1K/1K resistors to establish voltage-divider bias to the MPSA42 switching transistor.    

Your suggestion of using pin 2 and 4 is also correct when using the TS-850's internal amp relay.  For me and a lot of ops, it's way too loud -- and slow.  His buffer circuit can key as fast as any amp can.  My only issue with his circuit is that there's an easy opportunity to replace the MPSA42 with a better switching device for protection back into the TS-850 that does not increase complexity nor expense.  
 
Paul, W9AC

I was using a NTE94 transistor in the circuit because I had a bunch of them.
https://www.nteinc.com/specs/10to99/pdf/nte94.pdf
I tested it with my meter and found that it was shorted(Base to Collector).  The failure occurred while I was tuning the amp.

I was so focused on finding a replacement board and checking out the amps keying circuit I overlooked the obvious.
73,
Bill
« Last Edit: September 13, 2019, 08:49:21 PM by KO4NR » Logged
WE6C
Member

Posts: 106




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« Reply #36 on: September 20, 2019, 04:35:06 AM »

I've been using this...

https://www.qsl.net/k0bx/amp.html

I did add a diode and used a transistor with higher ratings than what's shown in the link. With this I can turn off the amplifier relay in the 850. Been using it for 3 or 4 years now.
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KO4NR
Member

Posts: 221




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« Reply #37 on: September 20, 2019, 05:59:17 AM »

I've been using this...

https://www.qsl.net/k0bx/amp.html

I did add a diode and used a transistor with higher ratings than what's shown in the link. With this I can turn off the amplifier relay in the 850. Been using it for 3 or 4 years now.
I was using the same circuit.  Had been operating fine for 14 years then it failed.  I used a NTE-94 transistor which had higher ratings as well.

73,
Bill
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