How to Hook Up an ICOM IC-705 to an Amplifier and Demonstration! - Livestream 

you don't need a supply to the relay as you switch the relay with the 705 output. when you key the mick, the volts drop to zero, i.e., the relays on a nc contact to the amp, to close the circuit.

I have the silver mx-P50M amp like on this video, can you post a solution? thanks :)

Hahaha. Just having fun. No intention of keeping the 705 on an amp.

Ooo we need this, I'm stuck with an Amp I can't use

Or just buy a cheap ebay relay module

there are better amps but a) without ATU (albeit having lower power consumption) - e.g. Juma or b) with ATU (and even better suited for portable operation) but with quite high price tag (diy599 PA500) my answer is, PA500 when portable, XPA125B when the convenience socket is available I have only QRP radios paired with PAs when needed

Yup

Already done looked acceptably clean with the Red version I have (2) but output drops about 20% on 10-15 meters. The silver version I had spurs showing and I had to put ferrite cores on all cables to keep it from oscillating. They look identical but not sure why this is true.

Lol, maybe.

And the optocouple just goes in then?

@@HamRadioCrashCourse If it can sink enough current which it probably can. You can try it with a switching transistor to prove the concept, though. You just have to take care with grounding. Did you have a chance to test how the IC-705 accessory pins behave unloaded?

@@HamRadioCrashCourse would love you to find a solution to this Jeff and postt a video :)

"The 705 has a 2SC1815 NPN-transistor on the SEND/ALC output with quite large (4.7k) base resistor, so it doesn't sink that much current." Nice. Maximum Collector Current |Ic max|: 0.15 A Forward Current Transfer Ratio (hFE), MIN: 70 At 4700 ohms and 12 volts, you get 2.55 milliamps into the base. With a gain of 70, you get 0.17 amps on the collector which is doubtless why the base resistor is 4700 ohms. The effective resistance will appear to be 12 (volts)/ 0.17 (amps) = 70.5 ohms apparent resistance to ground. The test, therefore, is to use a 70 ohm resistor on the keying input to the amplifier and see if it can operate the relay. Probably not. So, as others have said, the keying line needs either a delicate relay (a reed would be ideal) or something like a low impedance mosfet.

It’s not the 705. It’s the amps in this case.

"I am looking for a transceiver for my base station ... You revealed some serious challenges presented by the IC705. " Starting with it isn't a base station. ;-)

You need a tuner that handle the power out of the amp and goes between the amp and the antenna.

Mainly wanted the 705 for the waterfall and portability. Amp for HF is all I need. 70cm is useless around here and I get out fine using an HT with 5 watts on 2m. IC7100 will do, just mounting and lack of portability is the only set back.

Get a Yaesu FT 891 and a FTM 300 for your jeep. You will have everything you need plus Wires X.

@@TXLorenzo too many radios, rather have one that covers all bands.

Can you use an amp on VHF / UHF in the same way as HF?

Trierd this, no joy.

​@@K9WHF What about diverting the voltage from the mic when you key it, to make it start the amplifier?

I did try setting output on hf to off. It still didn’t work.

I just tried it again. There is voltage on the send pin when I am not keyed. When I key down. It doesn’t change.

Guy on Ebay is selling a "Icom IC-705 Amplifier Relay Cable WITH ALC ". for $17.95. Looks like a 6 ft cable with 2 RCA plugs on one end and a mini stereo plug on the other end. I bought about the same thing from him for my 7100, it included a "buffer relay".

Would love a diy of the circuit

It can be a relay, the rig switches a 12V relay and the amp is connected to the switched contacts. A modern rig can switch an ancient valve amp with higher voltage/ current requirements. This can be done solid state but a really is very reliable.

This is likely.

Yep. I run a keying interface to make it work.

@@HamRadioCrashCourse thanks for the reply.... Have you. / will you have a video on this?

Yes. I’ve used a few now.

Have the IC-705 and the RM ITALY HLA 305 using the 3.5mm to RCA Versa Tuner II; Zero issues from 0% to 100% 10 watts just rocks 250+ Watts (MFJ-941E). kf5yub

IT DOES KEY AMPS. I hooked it first to my KPA1500. On 20m I get about 400 watts out with 10 watts from the 705 I then hooked it to my XIEGU XPA125B. With the ATU on, and in MANUAL 20m mode, it keys fine. I get about 110 watts out with 1 watt in. (called a XPA125 because it is supposed to do 125 if needed). So the special RADIO/AMP keying cable? A standard 3/32 Stereo cable with two RCA jacks on the other end. From the radio, Tip and barrel is PTT. Ring and barrel is ALC (which I am not using yet. On my audio cable that made the RED RCA plug the ALC and the WHITE RCA the PTT. Your cable the colors might be different. The radio came set to low key. That cable I just plugged into the PTT RCA jack on the KPA1500. The 6 pin, mini DIN that plugs into the XPA125B has a PTT line, ALC, and tune pins. I cut the cable off of a old mouse that had a 6pin DIN and wired a RCA jacks for PTT and ALC. Then just plugged in the cable from the radio. Setting the XPA125 on Manual and just setting it on the band you want to use works fine. I have not tried ALC. Nor trying to match the voltages to auto tune bands. The 705 can do this and the 125B can use them. But, from the charts I see, the voltages for each band are different. The 705 does key and work on DSTAR HF VOICE on all the bands, 160 thru 440. Tho, only 10 watts on DSTAR HF Voice might not get you far until the sunspots get better, a amp will make it useful. I have used an ICOM 7300 a lot. I have a 7610 and 9700. The screen is the same size as the 7300 and 9700. And the menus are about same. I read all my memories from my 7100 into the ICOM 7100 software and then pasted them into the ICOM 705 software. When RT Systems comes out with 705 software life will be easier.

Wow. Great comment. I love the idea of repurposing the mouse. In my case. Which you likely saw I used pin out wires to connect the 705 to the din cable. I tried both high and low keying and could not get the amp to key. I wondering if I had something wrong with the wiring now? But I doubled checked it a few times. Hmmmm.

@@kenthufford743 Where did you find any info on the band output from the IC-705? From everything I can find, that data is only available via USB port. Also, according to the pin-out in the IC-705 manual, the ALC ring should be set to -4V - 0V when using a non-Icom external amp. So I was thinking it needed to be grounded. Did you happen to measure what the X125B outputs on the ALC port? Also, the X125B has a bold blurb about not connecting a voltage higher than 3.2V to the PTT port or it can fry the amp's CPU. Is the IC-705 voltage level on the send line not above that when not keying (was thinking I saw it was 5V)? I would like to build an interface that automatically band select the 125B but that would be massive if USB is the only way to get that information.

@@TheOriginalCheezWiz I have not hooked up the ALC line. The PTT line measures 4.5vdc. The 125b key line measures 9.0vdc. I have only used the 125B ATU in MANUAL mode. There might be band data on the TUNER jack. ML&S has a video showing a direct connect cable they sell between a 705 and the 125B they sell.

As the amp, is a smart amp, it can auto tune for given frequency, and can also adjust the radios settings. Bidirectional communication. Not 1 way ptt

I used a 100 watt Klm amp with my 817 years ago and it was a perfect match, clean signal, no hash, beautiful sine wave.

As an electrical engineer, it seems to me that the amp's 12v and the radio's output that is floating at ~2v when RX and low when TX need to be connected. The GND on both sides needs to be tied together. the remaining pin may just be open. The radio is then "shorting" the 12 to GND as you are doing with your wire. If you're concerned about possible damage you can add a resistor to the path to limit the current. Hope you get it fixed. 73's good luck

Thanks for clarifying that. It seems there are few issues with the keying of the amp that could use some help.

@@HamRadioCrashCourse did you fix it yet?

Watch then video. I said the same thing. Buy a 7300 for home.

@@HamRadioCrashCourse Yes I agree. But some people would make a mistake to buy a qrp radio and due to the poor propagation and maybe not optimal antenna, get nowhere. So the decision could be made to use more power. At the end, they have a lot of boxes connected, and still no joy. To have fun with qrp, Your antenna system must be optimal and with a good low loss coax to start with.

Sure. But people will still do it.

@@HamRadioCrashCourse True some forever will do strange things, we wish we had the extra funds needed to do them. lol

Most hf radios can go down to 5 watts. The main advantage to this radio is portability. It's basically a portable Ic7300. Personally I like the Ft817 for portable Qrp. My radio is at Yaesu to get repaired but can't wait to get it back and hook it up to my new wolf river coil!

@@HamRadioCrashCourseAn amp defeats the whole purpose behind getting a 15 watt radio! And for the price you might as well just get an Ic7300.

David Hook One good thing is you also get the VHF and UHF bands plus you don’t need to carry around a heavy power supply.