You are right to warn about connecting an Eagle (or any other modern radio) to
an SB-200 without a keying change. I am guessing that far more damage would be
done to the Eagle than just to the keying interface! -120 VDC on pin 8 of the
accessory connector would likely damage just about everything in the radio
since there is no relay (or optical isolator) in there to isolate errant
voltages from the other circuits in the radio.
The keying line in the Eagle is keyed by Q8, which is keyed through Q6 by the
“T” line in the radio. -110 VDC here will apply -110 VDC to the “T” line and
then to all other power lines in the radio - complete destruction of the radio
will be the result.
Even converting to a 12 VDC T/R relay might pose issues since there is a pretty
low current limit for the Eagle keying line. Also, flyback voltage from the
relay can also damage the Eagle.
A properly designed keying interface is the safe way to go.
Gary
W0DVN
> On Feb 25, 2020, at 10:39 AM, Bob McGraw K4TAX <rmcgraw@blomand.net> wrote:
>
> WOAH! STOP! If the amp has not been modified for the KEY circuit, it
> has 120 volts on the center pin of the RCA connector. If this is connected
> to the Eagle it will immediately destroy the Eagle PTT Amp control circuit.
>
> The amp relay must be changed to a 12 volt relay and other circuit
> modifications done, OR you must use an Amp Interface between the radio and
> the amp.
>
> Who ever gave you the information DOES NOT know what they are talking about.
> This is normal for most hams unless they have actually interfaced the SB-200
> to the Eagle. MFJ did make an interface suitable for the application.
>
> As Will Rogers said: "it's not what people know that concerns me, it is what
> they know that is not correct that gives me concerns".
>
> If you need additional information, I'll be glad to assist.
>
> 73
>
> Bob, K4TAX
>
>
> On 2/25/2020 8:13 AM, Richard Wagner via TenTec wrote:
>> I’ve never dealt with an Amplifier before. A friend gave me a Heath SB-200.
>> It appears I have to make a connection between the AMP KEY terminal of the
>> ACC-1 accessory connector and the AMP KEY Socket of the amp. A plug for the
>> socket and short jumper wire were included with my Eagle. This appears to be
>> all that is needed. I’ll connect from the Eagle to the Amp then through my
>> Antenna Tuner to the Antenna. Does this seem OK?
>>
>> Rich Wagner
>> K4MZE
>> _______________________________________________
>> TenTec mailing list
>> TenTec@contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>
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