Converting old president grant SSB 5 pin to 4 pin

[Jim Dickey]

I'm not going to order the adapter plug because I have spare 4 pin sockets. I got this radio without a mic but it powers on and everything seems to be working as far as I can test it without a mic. I've done a lot of searching and it seems I need to join pins 2 and 4 (shield and switch wire) together into the shield pin on the 4 pin cobra. One website says not to do this because of "unexpected" results. How do I make this work with the 28 different cobra mics I have?

 

[sonoma]

I have tried this 2 times and one it worked and one it did not. had one heck of a squeal no matter what I did. the one that worked I put a capacitor on one of the grounds. not real sure if that helped or not. seperated the grounds inside the radio
Nomad is the guru on this item. he will more than likely chime in.

 

[fourstringburn]

I'm not going to order the adapter plug because I have spare 4 pin sockets. I got this radio without a mic but it powers on and everything seems to be working as far as I can test it without a mic. I've done a lot of searching and it seems I need to join pins 2 and 4 (shield and switch wire) together into the shield pin on the 4 pin cobra. One website says not to do this because of "unexpected" results. How do I make this work with the 28 different cobra mics I have?

Why don't you just swap the 5 pin head with the 4 pin mic you want to use? I've done this with all my radio's with different mic pins. They are all a universal fit except the larger 8 pin of course.

In most cases, you only need 3 wires for President radios. The other 2 are for up/down buttons that don't need to be connected.

There is plenty of info online if you need the mic pinout info so can match them up accordingly.

 

[nomadradio]

Just to start, there is a math problem. Five doesn't equal four. The four-pin mike has only one ground wire, used for both audio and for the transmit/receive switch. The five-pin mike has two separate ground wires. One on pin 2 for JUST for mike audio, and pin 4 is just for the T/R switching. Using two separate grounds simplified the design of the radio's circuit board. And made life forever more complicated for the guy with a 4-wire cord on his mike.

This subject has been getting the "Well I tried it and it was okay" treatment since the 5-pin SSB radios first appeared 39 years ago. The world was full of D104 mikes with 4-wire cords. Everybody wanted to use that mike on his Cobra 2000/142/Washington/Madison/Grant radio. The 6-wire mikes became easy to find around that time, and gradually replaced mikes with only 4 wires in the cord.

The three choices are:

Connect ground ONLY to pin 2.

Connect ground ONLY to pin 4.

Tie 2 and 4 together.

The RISK! (mind you I said 'risk', not 'certainty') is that option one gets you a squeal on SSB receive. Option two risks a squeal on transmit, and option three can provide both.

But you might get away with it. Never could figure out how to predict this.

We use the converter board for a different reason. The only way to put a Roger K, bump-bump or five-tone beep in a Cobra 2000 is to add a relay. Those 'beep' boards don't have a relay to shut off the speaker while the board is holding the radio keyed. Can blow out your speaker.

But once the relay is installed, you're only using three pins out of five now. Ground, audio and transmit. Leaving the 5-pin jack in place for three pins seems demented, so we would change the mike socket as well whenever that accessory got installed.

Got really tired of wiring up this business by hand, and put it all onto a pc board.

Sure, it lets you use a 4-pin mike whether it's to accomodate a beep or not. And it eliminates the risk of feedback trouble.

And THAT's the difference between a commercial-quality job and a "what can I get away with" job.

Feel free to try whatever hookup you like. Clearly you MIGHT get away with it. And if not, it WAS your time to waste seeing if the cheap option would work well enough.

But for what I charge, the radio needs to work when it gets home. A trick that "might" work is not good enough. A sure thing is the only option that interests me.

What's good enough for you is for you to decide.

Oh, and I worked out a fix for the loud "POP!" from the speaker when you unkey.

Fair warning, the single-relay setup seen in those other posts had a drawback. A POP! from the speaker when you unkey.

It's just a timing issue. If you slide your thumb off the button on a hand mike, so that it snaps out faster than your thumb would allow, you can simulate this problem. Make that switch travel fast enough and you'll hear the POP that way. But if you unkey in the normal way, there's no problem. Your thumb takes a twentieth of a second or so to make the trip from where transmit shuts off, and the speaker turns back on. The switch in the mike is designed to "break before make", shutting off transmit before the receiver gets connected back to the speaker.

I couldn't find a relay that will break the transmit side and then wait a while before turning the speaker back on. Finally redesigned it to use two relays. One of them unkeys the transmit side immediately. The other relay 'hangs' with a small capacitor for about a twentieth of a second. The second relay activates the speaker only after the POP has died away, and you won't hear it.

Here's one wired in a Cobra 2000:

Seems like an obsessive sort of attitude to take, but that POP got on my nerves.

73

 

[sonoma]

Nomadradio can explain all of this very well. hope he answered all your questions. when I tried my 2 years ago he jumped in on this problem. I know one would squeal very nice on tx. we talked about this problem back when I had the one to squeal. I was lost trying to figure out what was wrong. like I said one I did never did act up. just luck of the draw for some reason.

 

[fourstringburn]

Wow!

That's a pretty involved process on that radio just to run a different mic.

My President HR2600's were childs play to change mics compared to the Grant model.

 

[Robb]

It can't be so involved.
Has anyone taken apart a 4 to 5 pin converter plug and look at how it is wired?

 

[fourstringburn]

That's what I thought , This radio has an unusual pinout configuration.

It has a transmit pinout but also a switch wire pinout, what's that for? The rest is similar to Cobra 4 pin wiring.

 

[Jim Dickey]

Just to start, there is a math problem. Five doesn't equal four. The four-pin mike has only one ground wire, used for both audio and for the transmit/receive switch. The five-pin mike has two separate ground wires. One on pin 2 for JUST for mike audio, and pin 4 is just for the T/R switching. Using two separate grounds simplified the design of the radio's circuit board. And made life forever more complicated for the guy with a 4-wire cord on his mike.

This subject has been getting the "Well I tried it and it was okay" treatment since the 5-pin SSB radios first appeared 39 years ago. The world was full of D104 mikes with 4-wire cords. Everybody wanted to use that mike on his Cobra 2000/142/Washington/Madison/Grant radio. The 6-wire mikes became easy to find around that time, and gradually replaced mikes with only 4 wires in the cord.

The three choices are:

Connect ground ONLY to pin 2.

Connect ground ONLY to pin 4.

Tie 2 and 4 together.

The RISK! (mind you I said 'risk', not 'certainty') is that option one gets you a squeal on SSB receive. Option two risks a squeal on transmit, and option three can provide both.

But you might get away with it. Never could figure out how to predict this.

We use the converter board for a different reason. The only way to put a Roger K, bump-bump or five-tone beep in a Cobra 2000 is to add a relay. Those 'beep' boards don't have a relay to shut off the speaker while the board is holding the radio keyed. Can blow out your speaker.

But once the relay is installed, you're only using three pins out of five now. Ground, audio and transmit. Leaving the 5-pin jack in place for three pins seems demented, so we would change the mike socket as well whenever that accessory got installed.

Got really tired of wiring up this business by hand, and put it all onto a pc board.

Sure, it lets you use a 4-pin mike whether it's to accomodate a beep or not. And it eliminates the risk of feedback trouble.

And THAT's the difference between a commercial-quality job and a "what can I get away with" job.

Feel free to try whatever hookup you like. Clearly you MIGHT get away with it. And if not, it WAS your time to waste seeing if the cheap option would work well enough.

But for what I charge, the radio needs to work when it gets home. A trick that "might" work is not good enough. A sure thing is the only option that interests me.

What's good enough for you is for you to decide.

Oh, and I worked out a fix for the loud "POP!" from the speaker when you unkey.

Fair warning, the single-relay setup seen in those other posts had a drawback. A POP! from the speaker when you unkey.

It's just a timing issue. If you slide your thumb off the button on a hand mike, so that it snaps out faster than your thumb would allow, you can simulate this problem. Make that switch travel fast enough and you'll hear the POP that way. But if you unkey in the normal way, there's no problem. Your thumb takes a twentieth of a second or so to make the trip from where transmit shuts off, and the speaker turns back on. The switch in the mike is designed to "break before make", shutting off transmit before the receiver gets connected back to the speaker.

I couldn't find a relay that will break the transmit side and then wait a while before turning the speaker back on. Finally redesigned it to use two relays. One of them unkeys the transmit side immediately. The other relay 'hangs' with a small capacitor for about a twentieth of a second. The second relay activates the speaker only after the POP has died away, and you won't hear it.

Here's one wired in a Cobra 2000:

Seems like an obsessive sort of attitude to take, but that POP got on my nerves.

73

Wow. Thank you for the thorough response, you don't get those very often in today's world of "k" text messages.

I guess I'll try it the easy way first (or all three easy options) then proceed to the copper board and the acid wash. Maybe I'll get lucky.

This is the first 8719 board radio I've played with, excited to do the channel expansion and I'm planning on making a replica of the uniden fm board to add that mode to the radio.

You wouldn't want to share your circuit for the relay board would you? I think I can figure it out from the picture but since you seem to know this stuff, I would trust your circuit over something I'm going to throw together with a trace pen.

I promise I won't mass produce your design.

Thanks much!

 

[Jim Dickey]

That's what I thought , This radio has an unusual pinout configuration.

It has a transmit pinout but also a switch wire pinout, what's that for? The rest is similar to Cobra 4 pin wiring.

It appears the switch wire changes the radio state from rx to tx independent (and perhaps redundant) from the tx and audio wires. I extended the board the original 5 pin was mounted to with some 4" leads to make experimentation a little easier. Going to try the 3 shortcut options first, then move on to relays. The radio will be operated with an external speaker and I can deal with the pop sound nomad mentioned, I'm thinking a large cap might soften the hard pop. Something in the 2200 uf range perhaps. We'll see if the radio even works with the shortcut wiring. If I at least get receive, I'll move on to the nomad level perfection we all strive for.

Where I'm at:

 

[Jim Dickey]

I crossed 2 and 4 from the 5 pin radio to pin 1 (top left facing the solder side with the notch up) of the cobra connector.

I must have done something backwards because now the Mic acts like a speaker when I key it. If there is good news, it's that the Mic doesn't squeal when keyed.

What did I do wrong? I'm using the following pinouts obtained from the web:

 

[nomadradio]

The one problem I see is that the 5-pin drawing is mirror-image.

If you look at the inside of the radio, the mike socket is wired the way it shows.

But looking at the pins inside the mike * PLUG *, it's the other way around,

The 4-pin diagram is correct, with pin 1 to the left of the notch, with the notch upwards.

The 5-pin diagram SHOULD be numbered in the same order as the 4-pin, with pin 1 to the left of the notch, numbered counterclockwise from there.

But the drawing is the other way around.

73

 

[nomadradio]

Oh, yeah. About that diagram.

Oops. Looks as if that file fell into a black hole. Haven't had too many hard-drive crashes since we switched to SSDs a while back. But it looks as if that schematic got created in a "Murphy Hole" between backups just before a crash.

Can't find it. The pcb artwork escaped oblivion, but the schemo did not.

I'll draw it up. Plans are to make a batch of fifty of these. Probably don't want to sell it without a way to provide a diagram for it.

There's no secret sauce there. Not worried about who does or doesn't copy it. I'll post it once I get it drawn up.

73

 

[Jim Dickey]

Well I'm at a bit of a stumbling point. I crossed pins 2 and 4 in to pin 1 of the cobra connector and hooked everything else up as I think it should be according to wire functions. Now I've tried 5 different 4 pin mics and they all seem to do something different. I tried a cobra ca73, a pierce Simpson from a lynx 23 base, a SBE powered base mic, and a procomm I just picked up at the local CB shop (NAPA). They had a new 5 pin mic in stock so I picked up one of those; a ProComm PSM5. MOST of the 4 pins I tried are still feeding audio through the Mic when keyed, one of the exceptions was a jc penny pinto SSB mic that would play audio through the speaker when keyed and through the Mic when un keyed. The sbe base mic worked on tx but but didn't divert audio to the speaker when un keyed.

I think I'm going to try re attaching the 5 pin plug and using the NAPA 5 pin mic. I'm really at a bit of a loss for why this thing is acting like this

 

[nomadradio]

(edit) Screwed up the schemo. Can't just delete and replace it inside the post, so I deleted the previous version with the corrected image below.

Okay, so here's the simple version. The one with the "POP!" problem when you unkey. Need more attention span to draw up the new version. Gotta do it, just not today.

The disc capacitors, ferrite bead and RF chokes reflect how many of my customers like to run high power. Didn't dare leave out filtering on a mike socket for those guys.

73