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Author Topic: Kenwood TS-850S Amp Buffer  (Read 1117 times)
VE3TMT
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Posts: 992




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« Reply #15 on: September 10, 2019, 03:23:11 PM »

With my 850, I use a simple external relay that feeds of the 12V and SEND lines from the radio to key the relay. The contacts in turn close the keying line on the FL2100B. Been using this simple approach for years, never had a single issue. Don't operate QSK so not a concern.

Max
VE3TMT
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KO4NR
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Posts: 221




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« Reply #16 on: September 10, 2019, 03:26:51 PM »

Your may also wish to place an RFC in the amp in series with the center connection of the keying circuit. Despite the two 0.01 bypass caps, you may be passing RF from the amp onto the keying line.

- Glenn W9IQ
Sure can't hurt.  What value RFC should I use?
Bill
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KO4NR
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Posts: 221




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« Reply #17 on: September 10, 2019, 03:31:18 PM »

With my 850, I use a simple external relay that feeds of the 12V and SEND lines from the radio to key the relay. The contacts in turn close the keying line on the FL2100B. Been using this simple approach for years, never had a single issue. Don't operate QSK so not a concern.

Max
VE3TMT
Sounds like a simple and reliable approach.  Thanks for the feedback.
73,
Bill
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W9IQ
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Posts: 3525




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« Reply #18 on: September 10, 2019, 03:56:58 PM »

I would shoot for at least 100 uH in order to provide sufficient impedance on the lower bands.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KO4NR
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Posts: 221




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« Reply #19 on: September 10, 2019, 04:12:11 PM »

I would shoot for at least 100 uH in order to provide sufficient impedance on the lower bands.

- Glenn W9IQ
Ok Glenn and Thank you!!
73,
Bill
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KM1H
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Posts: 5513




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« Reply #20 on: September 11, 2019, 05:54:37 PM »

RCA connectors and jacks are notorious for developing poor grounds over time, especially in a  environment such as high humidity NH in the summer. My pair of Drake C Lines and other gear that used them suffered until I regularly cleaned them. This was before DeOxit.

Carl
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KO4NR
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Posts: 221




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« Reply #21 on: September 11, 2019, 07:19:32 PM »

RCA connectors and jacks are notorious for developing poor grounds over time, especially in a  environment such as high humidity NH in the summer. My pair of Drake C Lines and other gear that used them suffered until I regularly cleaned them. This was before DeOxit.

Carl
Thanks for the heads up Carl!!
73, Bill KO4NR
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N3AJB
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Posts: 60




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« Reply #22 on: September 12, 2019, 07:12:18 AM »

Below is a link to a video from Mr Carlson's Labs in which he discusses a buffer circuit for new transceivers and older amps which might use 120 VDC antenna relay keying voltages. 

Of course the circuit will work with any amplifier.  The transistor is the MPSA 92 which can handle up to 300V and costs $.22.  I had to buy 50 on Ebay for around $5.00.

It's a very simple circuit and easy to fabricate. 

If you advance to the 10 minute mark you'll find his discussion of the circuit.  However, I found the entire video very interesting.   JON


https://www.youtube.com/watch?v=FHxOI_iSmcM
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W9AC
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« Reply #23 on: September 13, 2019, 05:04:01 AM »

Of course the circuit will work with any amplifier.  The transistor is the MPSA 92 which can handle up to 300V and costs $.22.  I had to buy 50 on Ebay for around $5.00.

FWIW, I'll add a few comments...

Addition of the flyback diode across the relay coil is always a good idea, especially on relays with large solenoids since they can produce a large amount of current when the magnetic field collapses.  The diode will also accelerate the relay's release time since the collapsing field no longer holds the relay as current is diverted into the flyback diode.

It's hard to believe the level of damage done to the PC board was due to this alone.  I'll deviate from Carlson's advice on this one -- not because his advice is bad but if the work is being done anyway, choose a better switching device.  I would not use a MPSA92 here.  It's also a PNP type and not NPN which is what would normally be used - so just be careful of polarity.  

Any time there's propensity for back current damage, I would use a Darlington at a minimum (e.g., TIP150 series).  A Darlington transistor is in effect two transistors in a single three-lead package.  A Darlington offers much better collector-to-base isolation than a BJT transistor like the MPSA92.  Several Darlington switching transistors contain an internal flyback diode.  The next level of protection is the addition of a Zener diode from the Darlington's base to circuit ground.

Stepping it up further, we can use one or even a balanced pair of IRF820 MOSFETS (See http://wb9kzy.com/keyallhv.htm ).  These are good for switching 400V AC or DC and a pair make the circuit polarity independent.  The IRFBG30 will switch up to 1KV.

Finally, use a (4N35 or PVI5080N) optocoupler on the MOSFET gates.  With just three components, you have a buffer that can safely switch a couple amps of current on any key line, old or new, and have the ultimate protection of photo isolation.  

I've designed my own buffers on PC boards and these can be seen on my QRZ page.  They are shown under the "KEY LINE INTERFACE" heading.

One alternative I've been experimenting with uses an Ixys CPC1978 solid-state relay in place of IRF820s (See http://www.ixysic.com/home/pdfs.nsf/www/CPC1978.pdf/$file/CPC1978.pdf ).  However, the on/off switching time is a few ms but in fact, they switch much faster than the spec and still plenty fast for nearly all keying and sequencing circuits.

Paul, W9AC


 
« Last Edit: September 13, 2019, 05:18:47 AM by W9AC » Logged
W9IQ
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« Reply #24 on: September 13, 2019, 05:21:22 AM »

That is all valid, Paul but in what way is that superior to simply using the dry T/R relay contacts provided by the TS-850?

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W9AC
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Posts: 135




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« Reply #25 on: September 13, 2019, 05:59:34 AM »

That is all valid, Paul but in what way is that superior to simply using the dry T/R relay contacts provided by the TS-850?
- Glenn W9IQ

Well, whatever caused the significant trauma to the circuit board would likely damage the TS-850s dry relay contacts.  I cannot imagine what caused that level of damage from the amp, but whatever it was, the amp should be fully isolated from the rig at least until the root cause is investigated.

Paul, W9AC
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KA5IPF
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« Reply #26 on: September 13, 2019, 06:52:24 AM »

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.
« Last Edit: September 13, 2019, 07:04:19 AM by KA5IPF » Logged
W9AC
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Posts: 135




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« Reply #27 on: September 13, 2019, 08:07:27 AM »

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
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KA5IPF
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« Reply #28 on: September 13, 2019, 10:26:25 AM »

I guess I missed his keying circuit he added. I see the original amp circuit but not his addition. That transistor had been overheated numerous times ergo the large dark area. It finally gave up.

Have fun, I can only tell you how the circuit was designed to be used and normal usage.
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KO4NR
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Posts: 221




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« Reply #29 on: September 13, 2019, 06:41:38 PM »

Excellent feedback and discussion!!  I appreciate it!!

I’ll go with the SSR.
http://www.crydom.com/en/products/catalog/mp-series-ac-pcb-mount.pdf
73,
Bill KO4NR
« Last Edit: September 13, 2019, 06:44:56 PM by KO4NR » Logged
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