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Electro-Voice 729SR Mic Schematic?

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rescue161

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I am in need of a schematic for an Electro-Voice 729SR microphone. It's fairly old as it was made in the 60's. It was my Grandfathers and I'd really like to get it up and running again. I did take it apart as there was no continuity when the mic was keyed. The leaf switch has become weak and now I have no idea what is normally closed/open. I do see there is a hole right through one of the leafs with burn marks around it.

It was used and will be used with an old Browning Mark III. Radio seems to work fine except for the mic issue.

Any help would be appreciated.

Thanks,
Scott
 

kb2vxa

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You may have the wrong model number, the EV 729 "banana mic" as we used to call it has only one set of NO contacts. Since it came "stock" with a number of Amateur and CB transceivers it may have been modified by the manufacturer.

"The leaf switch has become weak..."
You can always bend it a little as I used to do with a number of similar switches.

"...and now I have no idea what is normally closed/open."
Oh good grief, which way do the armature(s) move when you press the actuator with your finger? That's how I figured it out, you can too.
 

rescue161

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Seeing as how the leaf switch is probably older than I am, I didn't want to bend it too much just to "test" out what I thought may have been the original configuration. A very nice person on another board sent an owners manual that has a schematic. The leaf switch has 4 leafs two of which are N.C. and two are N.O. when not transmitting and reversed when transmitting. They were definitely not in that position during initial inspection.

Got the mic squared away, now to find out why the old Mark III isn't transmitting...
 

kb2vxa

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No, you don't have to bend it too much, a slight kink in the right spot with needle nose pliers is quite enough. (;->) Ah, nice to know you got the schizmo for that particular factory modified mic, they just put a different switch in it and I had no way of knowing which one.

How you're going to hook it up to a Browning Mark III I have no idea but good luck with it. (;->)
 
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rescue161

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It was easy to interface with the Browning. I have the schematic for it too. :wink:

It was already partially wired for the Browning as it was, but the leaf switch was out of whack and it wouldn't work. It works now, but the transmitter just ain't transmitting. There are a lot of tubes in this thing and tubes I know not... I know transistors, but not tubes.
 

kb2vxa

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Too bad I'm here and you're way over there, tubes are my specialty and Browning is an old friend. <sigh> Find an old fart in your area, someone who knows what a boat anchor is besides something you throw in the water. A good place to start is in the AM window on 75 or 40, maybe a local net on 10? On the other hand a local club may be of some help, just look for the blue hairs. What you need is hands on, repair by remote control is difficult at best.
 

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Hello Scott:

I am sure the mic will wire up to the Eagle, and you can always use a external switch that is loated on the mic. Look at Welcome to CBTricks for Browning diagrams.

I have a very expensive swap meet Commercial Mic black taped onto a cheap Mic stand, and a spring loaded switch for the PTT or transmit function also black taped onto the mic stand. Yeah it doesn't look like we are going to be invited to the Paris Air Show due to its looks, but it works and sounds great!

There are other EV 729SR Mic's out there on E-Bay and such that you might get a new switch. Maybe a simple mini switch taped to the side of the Mic to get yeah going?

Good Luck.

Jay in the Mojave


I am in need of a schematic for an Electro-Voice 729SR microphone. It's fairly old as it was made in the 60's. It was my Grandfathers and I'd really like to get it up and running again. I did take it apart as there was no continuity when the mic was keyed. The leaf switch has become weak and now I have no idea what is normally closed/open. I do see there is a hole right through one of the leafs with burn marks around it.

It was used and will be used with an old Browning Mark III. Radio seems to work fine except for the mic issue.

Any help would be appreciated.

Thanks,
Scott
 

rescue161

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Good news!

Got the old Mark III running again. I was looking at K1's contacts being bad/dirty or that the 7558 tube was possibly bad. Following the schematic back, I decided to troubleshoot in all modes and switched the radio to LSB. I saw deflection on the Watt meter. Moved the mode selector back and forth and it's working like a champ.

So, I'm off to get some cleaner for the mode selector as it is contaminated with old cigarette tar residue and is very hard to turn. Hopefully I can remove most of the crud without having to disassemble the switch. Already had to do that on the Siltronix VFO.

The radio works great now that I rewired the mic. Hopefully I'll have her back on the air before tonight. I got great signal reports during my tests.
 

kb2vxa

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Ah, now we're getting somewhere! Those multiple sets of contacts on the mic switch misled me into thinking the rig uses "electronic switching" but K1 tells me it's a relay which only requires one NO contact set to close in order to key the transmitter. Oh well, that's what happens when I don't have a schematic.

Yup, now you need to do something you should have done first off, clean the switches and pots. For this job I recommend DeOxit made by Caig, cleans like a champ and doesn't leave a lubricant residue to gum up on you later on. Then there are the relay and mic switch contacts, here you use a strip of heavy, rough paper slipped between the contacts and wiggled around while applying pressure to hold the contacts closed against the paper.

I always liked that microphone and have used them on several CB and Amateur rigs. It sounds great and gives best results when held about 6" from the mouth and off to the side slightly, "eating" it only makes it sound muffled and it picks up breath sounds rather easily.

Just a bit of advice as if you didn't see it coming, set aside that "slider" and operate legally. That having been said you'll save yourself other headaches, those things are unstable and if nobody has told you let me be the first, anything with the Siltronix name on it is pure crap. I cringed when I heard that name mentioned on the air and thought "it figures" when connected with garbage signals having chirps, a strong FM component and drift. Then the infamous 1011 was one of the original splatter boxes but I digress.

Now why don't you get yourself the other Browning and use the VFO for target practice? (;->)
 

rescue161

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Even better news!

I don't need the external Siltronix VFO. The more I mess around with this thing, the more I find out. Apparently, my Grandfather modified the crap out of this thing... Channels 2-15 and 17-23 all work as they are suppose to. Channel 16 is not working (probably a bad crystal). Here's the good part - Channel 1 is the VFO! Once the radio is on channel 1, the transmitter is tuned via the receivers channel selector, so I can go anywhere from 26.955 to 27.605! I've been racking my brain all day trying to get the Siltronix VFO to work, but it was competing with the "internal VFO" that he set up years ago.

I found this after getting frustrated that the channels were not displaying correctly, so I did a channel to frequency comparison without the external VFO hooked up. I noticed that channel 1 was transmitting on channel 19. At one point during my tests, I noticed that channel 1 had changed (I had inadvertently moved the band selector on the receiver).

Once I figured out what was going on, I undid the coax that I soldered in for the external VFO and am now good to go.

Has anyone ever heard of this mod before? It looks like he was sampling the receiver RF and using it via K1 in the transmitter. I am using an external frequency counter in line with the antenna, but would LOVE to wire it directly to the radio so I don't have to transmit to find out what channel I am on. Anyone have any ideas?

Scott

ps, I did clean off the mode selector, but it's still dirty as all get out. Looks like I'm going to have to dismantle it and clean it the hard way.
 

rescue161

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More good news...

Just made a few contacts on SSB and all is well. Talked to someone from MO and one in FL from here in NC. Some others on other boards made mention that the SSB on the Mark III, especially ones used with external VFOs were not user friendly or just plain did not work at all.

This radio is HOT! My Grandfather did good with whatever he did to it. It's still only putting out about 4 Watts or so on AM too!
 
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