[TenTec] Keying Mod for Model 405 AMP

[rick@dj0ip.de]

I was asked about my keying mod to the Model 405 amp.
I thought it was posted on my web but I guess I forgot this one.

Today I uploaded my keying mod for this amp to enable using it with more
modern QRP transceivers, such as the Argonaut 6, the FTDM-DUO and of course
my own Aerial-51 SKY-SDR transceiver.

http://www.dj0ip.de/ten-tec-stuff/405-keying-mod/ 

CAUTION:  This mod 'only' enables keying with a transceiver using open
collector AMP KEY keying.
It does not address the timing issue, where the 405 should have the AMP KEY
line active about 15 mS BEFORE  RF arrives at the amplifier.

The Argo6 has 17ms so it works just fine.
My SKY-SDR also has the necessary delay (by default).
For other transceiver types, do your own due diligence. and remember, this
is usually a software adjustable parameter in the transceiver and in default
mode is probably not set correctly.  Set it for a value between 15 and 25
mS.

B T W . . .  in 1975 when the 405 originally shipped, it used Carrier
Operated Relay (COR) to switch its T/R relay.  This was a disaster, always
hot switching.  I designed a Mod that buffered the Argonaut 505's "T" line
and then sent +12v to the amp.  I used this to drive switching transistors
in the 405, thus speeding up the relay's switching time.   THAT WAS A
DIFFERENT MOD, NOT THE SAME AS THIS MOD.

And I dunno if I could even find that mod again - that was 42 years ago.
This time I would do it differently.  I would use the Argonaut's T-line to
switch an Open Collector transistor, connect it to one of the spare RCA
phono jacks on the rear panel of the Argonaut 505/509 and then modify the
405 as described in the mod now on my web page.  In other words I would
modify the Argonaut to make it work like a modern transceiver with an AMP
KEY line and use together with the MOD described on my web now.

DON'T FORGET:  The original Argonaut only had about 3 Watts of output and
that was all that was required to drive the 405 to full power.  Today's QRP
radios usually put out more like 10w and can easily overdrive the 405.  DO
NOT OVERDRIVE IT!

Gud Luk.

73
Rick, DJ0IP