Re: Wanted Tohtsu CX600NC relay

Colin Ranson

Same here no matter what I always, under advice from G3XDY/G4DDK and the VHF/UHF DX book, use an isolating relay...... however the tiny SMD relay in my HA8ET 70cm pre-amp has so far enabled the device to  survive, used last night in the 70cm  UKAC with 250w.




Colin de G8LBS.


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From: ian hope (2E0IJH)
Sent: 09 September 2020 15:07
Subject: Re: [UKMicrowaves] Wanted Tohtsu CX600NC relay


I always use preamps that have internal bypass relays, even if they are only on the RX line and drop the power to those before switching the mast head relay, we use either cx520's or Cx600's depending on application, But as Ian says the older versions of both the cx600 and the cx520 had a different design.






Sent: Wednesday, September 09, 2020 at 2:47 PM
From: "Ian White" <gm3sek@...>
Subject: Re: [UKMicrowaves] Wanted Tohtsu CX600NC relay

By having the common port pointing the opposite way from the other two, the CX520D saves a lot of space inside a preamp box. I wish there was a wider choice of relays with that connector layout, and at a similar price point (which rules out the big, expensive EME relays) but I have never found even one alternative.

However, the problems with poor isolation and poor power handling are surprising. I used the same CX520D in the 70cm EME preamp for many years, handling 1kW CW and connected directly to the GaAsFET preamp, all with no damage. So does the performance really fall over a cliff between 432MHz and 1296MHz?

A possible explanation for poor isolation is that there have been at least two versions of that relay, sold under the same model number. In the modern ones, the isolated contacts are grounded onto gold-plated contacts that are screwed into the body. The older ones relied on grounding onto the body itself, which is a poorer contact and also less reliable... bearing in mind that the relay will be operated tens or hundreds of thousands of times, but preamp only has to be unlucky once.

Yet another thought is about the settings of the moving arms and the actuator plungers. These settings are quite critical to achieve the correct contact pressures, and the TohTsu relays aren't exactly built like Swiss watches.

As I said, I do wish there were other relays with that highly practical port layout and at a similar price point.

73 from Ian GM3SEK



On 09/09/2020 13:29, Colin Ranson wrote:

Andy,    I think the CX3500 is a copy of the venerable Amphenol 316-10744 series, of which I was fortunate enough to rescue several from a defunct H.O. RF switching station many years ago.   One was 48v, the rest were 26v except one which was 12v !    These are just as good, if not better than the Tohtsu, in build quality at least.


What is rare, and I would love one for an application, is the same build but the common (centre) N connector coming out at 180 degrees so that the common can poke out of a plastic (mast head pre-amp) box for connection to the antenna.   Unfortunately the Tohtsu CX520 just does not cut it as far as isolation or power handling is concerned. I burnt one out with 23cm at 240w even when properly sequenced.


Regards Colin de G8LBS.


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From: Richard GD8EXI
Sent: 08 September 2020 23:05
Subject: Re: [UKMicrowaves] Wanted Tohtsu CX600NC relay


    I have one which was retired from active service many years ago as the isolation was not good enough on 432MHz and above, destroying the preamp device. I might sell it but, what band is it for and how much isolation do you need. I can re measure it but from memory it was less than 40dB of isolation on 432 MHz and above, not enough if you are running 100watts plus.

A CX3500 is much better, if you need good isolation, as it has a double switch and the unused bar is grounded both ends. The isolation is so good it is difficult to measure, being in my experience greater than they 65dB they claim, more like 80dB even on 1296MHz.


On 08/09/2020, 21:20, "Andy GD1MIP" <gd1mip@...> wrote:

Hi, I need a Tohtsu CX600NC 12v DC relay.

Before I buy new from a store does anyone have a spare they'd like to sell?

Thanks Andy GD1MIP



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