Connecting a 5000a to Ameritron AL-811 Questions

NY2A · September 2023

Warning: I am about to display my shameless, no-code Extra, lack of basic knowledge.

I recently received a used - but little used - Ameritron AL-811 Amp and want to connect it to my 5000A through the Ameritron ARB-704 keying relay that came with the amp.

First question: the ARB-704 has internal jumpers that must be configured to match the keying voltage present at the RCA plugs on the 5000a. I measure a fluctuating voltage of between 0.04 and 0.07 when the circuit is open, and a voltage of 0.6 when closed. So, approximately half-a-volt difference between open and closed. Problem is, this doesn’t come close to any of the jumper configurations in the ARB-704 manual (available here). What am I missing?

Second question: Both the amp and the ARB-704 have RCA plugs for the ALC line, but the 5000A doesn’t have a dedicated ALC input, just the three “External Keying Line” RCA plugs, which themselves are configurable via PowerSDR (I use KE9NS’s latest version). However, configuration as an ALC input doesn’t seem possible. Does that mean the 5000a doesn’t have the ability to receive ALC feedback from the amp? That doesn’t seem likely to me. So again, what am I missing.

Thanks in advance for (hopefully) educating me.

73 de Tony NY2A

cfclaver · October 2023

Tony,

Not sure if you have figured this out yet. I am a long time owner of a Flex5000a -excellent radio!

The keying circuit uses a Darlington transistor and can switch up 50V but no more than 400ma. See owners manual Page 9. I am not familiar with the ARB-704. Having glanced at the description of the 704 I don't think you have to worry too much about the radio to 704 connection. The 704 is meant to protect the radio from the amplifier.

All you need to do is configure the ARB-704 for the Radio TX low system (non IC705). This will present 5v open circuit to your Flex 5000. When keyed the Flex will pull this voltage to ground and sink about 100 micro-amps at the Flex. This is easily handled by the Flex keying transistors. When this line is pulled to ground it will key the amplifier connected to the "amp" port using the ARB-704.

On my 5000a I use a small dedicated opto-isolated relay board to key my Henry 4K Ultra. These are available on Amazon for less than 10$. The 4K has about 30v at the key port and sinks an amp or so. I learned the hard way that the 5000as couldn't handle the current. Page 9 of the owners manuals spells this out fairly clearly now.

Good luck and enjoy the extra gas with the amplifier.

73s,

Chuck de NJ6D / N7KUI

Connecting a 5000a to Ameritron AL-811 Questions

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