FA-PA50 linear amplifier with Elecraft rigs

Hi Vincent,

welcome to this forum.

Sorry I cant help you but there has been a thread here already about this question about two years ago :

K2 mit FAPA50 betreiben

Its in German language but perhaps you can use Google translator and the included link in second posting is helpful for you.

If you have problems with Google Translation I can try to translate it.

73 / 72 and have a nice evening!

Peter DL3NAA

Quote from dl3naa

Google translator

I'll prefer https://www.deepl.com/translator

Much much better than google.

Peter, probiers mal aus, ist klasse, das Teil. Der Tipp kam übrigens hier aus dem Forum. Bin seitdem Fan von deepl. Kannst viel verändern und passende / bessere Begriffe im Text einbauen. Zudem Made in Germany. Steht im Impressung und die Pressestimmen kann ich nur bestätigen. Deepl benutzt zwar einige Tools von google, ist aber bei weitem nicht so "gesprächig".

Hi Vincent,

as written in the linked thread I used the K2 together with the FA-PA50.

Therefore I used a modified version of the circuit described in the links:

http://www.mwrs.org.au/2014/04/20/ele…keying-circuit/

https://ftp.elecraft.com/K2/Mod%20Notes…g%20Circuit.pdf (new link) - I think the one that you have built in your K2.

Just if you are interested: My modification is to use a voltage divider (out of two 1k Ohm Resistors) to use it with the connector of the KIO2 PC-Interface (that serves only 12V instead of 6V), because did not want to build this inside my K2. You can see my version in the attached pictures.

The version without the modification should work perfectly fine.

The setup is quite simple: You must only configure the PA to be low-active as described in the manual and connect the PTT-jack of the transciever with the one from the PA. Then the interface should work without problems, like it did in my case.

I wish you much fun and success with your project.

73 de Olaf, DL6OH

Quote from Ea3ADV

I understand that in the KX3 I should configure the ACC2 port through the menu.

Hi Vincent,

thats a misunderstanding. For PTT there is nothing to configure in the KX3 Menu! Just take the signal on the ring (plus ground) which pulls the external device PTT Line to ground. For correct use, the PA must be configured to low active as Olaf, DL6OK wrote in his posting.

Here is what the KX3 manual says:

Keyline Out and GPIO (ACC2)
The 2.5-mm stereo ACC2 jack provides a keyline
output (ring contact) and a general-purpose 3-volt
logic signal (tip contact).
The keyline output goes low during transmit, and
can be used for transmit/receive switching of linear
amplifiers and transverters. For keyline voltage and
current limits, see Specifications.
The general-purpose signal, GPIO, can be set up for
various equipment control functions. For example,
it can send band-change information to Elecraft
XV-series transverters. See the ACC2 IO menu
entry for a full list of uses for this signal, as well as
hardware interface requirements.

Hi Vicenç,

The FA-50 has a switch on the front panel to insert an attenuater.

The KX3 is capable of much more output power than it takes to blow the final transistors in the amp.

I know from experience

You must be sure the attenuater is switched in ALL THE TIME.

My transistors were replaced, and the switch hard-wired so that the attenuater cannot be switched out.

73 - Rick, DJ0IP

Vicenç,

One more important point: CAUTION, DO NOT OVERDRIVE THE AMP

The Hardrock-50 is spec'd to be driven with 5 Watts.

Your Transceiver can put out more than 10 Watts. This amount of power will probably kill the transistors in your amp.

I strongly suggest you install a 3dB pad inside of the amp to prevent it from being over-driven by the radio.

I will attach the schematic of 3dB pad used inside of the FA-50 amplifier.

The resistors are 2 Watt resistors.

Believe me, the transistors die much faster than you think.

I speak with painful experience!

73 - Rick, DJ0IP

My Hardrock-50 didn't die with a 10-15 Watt drive from the KX3. Maybe the FA-50 PA is more sensitive than the Hardrock-50?

73, Peter - HB9PJT

Maybe. Still it does not hurt to place a pad in the amp, unless you have a second QRP transceiver which only has a few watts output power.

Replacement transistors are not cheap!

73 - Rick