[Elecraft] Ijterface between 30L1 and K3

[Don Wilhelm]

John,

This answer applies to ANY amplfier, and is not specific to the Collins 
30L1 - follow these steps for any amplifier to verify that the K3 can be 
safely connected.

With any amplifier, the connections to the K3 are from KEYOUT to 
whatever amplifier input activates the T/R relay - some label it KEY-IN, 
others label it PTT and there are a few other designations - consult 
your amplifier's documentation for details.  I will refer to it as "PTT" 
in the points following.

Now that you have identified the amp's input to activate the T/R 
switching, check to see if it ias compatible with the K3.  With your 
DMM, measure the open circuit voltage on the "PTT" input to your 
amplifier.  Is it positive?  Is it less than 200 volts?  If the answer 
is YES to both questions, then go on to the next step, but if either 
answer is NO, you must provide some type of interface (relay) between 
the amp and the K3 (the Heath SB-200 and SB220 have negative voltages 
and cannot be directly connected to the K3).

OK, the next step is to measure the current - set your DMM to measure 
current, and connect one probe to the amp's PTT input and the other to 
ground. With power applied to the amplifier,  if the current indicated 
on your DMM is less than 5 amps, the K3 KEYOUT can handle it.

Connect the K3 KEYOUT to the amp's PTT IN, and connect a coax between 
the K3 RF Out and the amp's RF IN.  That is all there is to it.
With vacuum tube amplifiers, if there is an ALC output, I do not 
recommend using it - just adjust the K3 power output to properly drive 
the amplifier.  If you insist on connecting the ALC, first make certain 
your K3 has the update for negative going ALC voltage, and connect the 
amp's ALC out to the K3 ALC input.  DO NOT use the ALC for power control 
since that will only lead to distortion.  You will still need to control 
the K3 output power to properly drive the amplifier without activating 
the amp's ALC output.

Many solid state amplifiers insist on connecting the ALC output to the 
exciter.  These amplifiers have fault detection circuits that want to 
reduce or shut down the driving transceiver in case of a detected fault 
condition.  The same rule applies - go ahead and connect the ALC output 
to the K3, but do not use it for power control, use the K3 power level 
to control the amplifier's power output.  If the amp determines that a 
fault condition exists, it can use the ALC connection to reduce the 
drive from the K3 to a safe level.

73,
Don W3FPR

John wrote:
> Gentlemen,
> While I am certain that this topic had its airing, I cannot find any 
> reference in the accumulation of the '...Digest' I have at hand.  At the 
> risk of resurrecting an old issue, I ask your indulgence and aid  in 
> obtaining information concerning the requirements / indiosyncracies 
> relating to conecting a K3 to a Collins 30L1 amplifier.
> Thnk you in advance for your consideration in this matter.
> John Kountz, KE6 
>
>