Browning Mark 3 transmitter. Save that meter.

[nomadradio]

Haven't played with Lazarus this week, hardly. Ordered the Tune and Load control capacitors from RF Parts. I'll feel more enthusiastic with those two parts in place.

In the meantime here's an angle from my day job. This particular Browning Mark 3 SSB transmitter is getting its AM/USB/LSB mode selector bypassed, making it a straight AM-only transmitter. Much cheaper than replacing the Mode switch.

But here is a step out of our "hot-wire" procedure to totally bypass the defective Mode Selector in the Browning Mark 3 SSB transmitter. The switch develops leakage across the insulation separating individual switch circuits.

One of the most annoying of these "across two circuits" leakage paths will affect the transmitter's meter. The symptom is that switching the meter select knob to "Mod" causes the meter to peg violently while receiving. Don't even have to key the mike. If you see this, PULL THE PLUG. NOW! Then you can turn the meter selector back to "SWR" or something safe.

The really annoying part is when the coil inside the meter burns out. Forever.

To avoid this we routinely bypass just the "Mod" meter circuit. Only involves two wires, and it's cheap insurance even if your mode selector appears to still be perfect. There is a major wear-and-tear angle to this breakdown, so a low-mileage transmitter may have no such problem.

Maybe not today, maybe not tomorrow, but soon. And for the rest of your life.

Sorta.

This trick simply unhooks the transmitter's meter from the mode selector. This will protect it from later failure of the selector down the road.

First, identify the two wires we'll be molesting.

The orange wire leads from the meter switch to the mode selector. The white/green wire leads from the modulation-voltage detector to the mode selector.

The white/green wire gets removed altogether. The orange wire gets cut near the mode selector so it will reach to the tie point where the white/green was just removed.

I wouldn't normally leave a stub of the white/green wire, but it serves to identify the correct lug.

And that's all there is to it. Remove one wire, the white/green and move the orange wire to where it used to be.

73

 

[vswr]

Just need some clarification. Does this mod only remove the ability to see your mod on the meter while protecting it, or do you lose the ssb also? Hopevthis isnt too much of a dumb question. Thanks!

 

[nomadradio]

This affects only the meter. It bypasses the mode selector. There's no 'modulation' measurement in sideband modes. Just serves to prevent meter damage if/when the mode selector suffers the most-common sort of breakdown later on. We've seen too many Mark 3 SSB meters hammered when the mode selector's insulation breaks down.

And no, it's not a dumb question.

73

 

[vswr]

This affects only the meter. It bypasses the mode selector. There's no 'modulation' measurement in sideband modes. Just serves to prevent meter damage if/when the mode selector suffers the most-common sort of breakdown later on. We've seen too many Mark 3 SSB meters hammered when the mode selector's insulation breaks down.

And no, it's not a dumb question.

73

Thanks. I was looking at the schematic. Why not just clip the wire from the mode switch, leaving a bit of the color on it, then put a small piece of heat shrink on each? Would that also work or does that wire feed or come from another circuit? I agree about the mod not required on ssb. Thats easily seen on the fwd rf position on any radio.its smart to protect the meter and oddly enough, there are a couple or more mods that Browning could have done straight from the factory. Especially the mic plug and jack being so proprietary and having vcc on pin 2 to fire off the relay when a 6 or 12 volt is much more common and can do the same job using its own transmitter voltages directly from a heater voltage into a brige rectifier.
73s

 

[nomadradio]

a 6 or 12 volt is much more common

The explanation is easy. Simplification. The 350-Volt B+ supply is already there. In bulk quantities the 110-Volt DC relay would cost just the same as one built for 12 Volts. Only calls for the one 10-Watt resistor to drop 200-odd volts and leave 100 or 110 for the relay coil. A separate rectifier and filter to power a 12-Volt DC relay would definitely raise the production cost over the price of one 10-Watt resistor. The choice of a 110-Volt relay coil was a common practice in the tube era, not confined to Browning at all. When we have to replace the unobtainable original Mark 3 relay, we use a 12-Volt DC relay and power it from two rectifiers and two electrolytic caps in a half-wave voltage doubler from the 6.3 VAC heater supply. A PNP transistor with the collector grounded handles the coil current so only the transistor's tiny base current gets piggybacked onto the mike cord's ground conductor. Naturally the socket has to get changed, but at least the hole cutout in the chassis is the same size as the new socket.

Seems to me I posted that procedure here somewhere. Does eliminate the shock hazard from a bad ground connection in the mike cord. If the ground comes loose, you key a metal mike and touch grounded metal you'll get lit up, big time.

73

 

[nomadradio]

Sure enough. Almost five years ago.

https://www.worldwidedx.com/threads/browning-mark-3-ssb-12-volt-relay-substitute.260265/

73

 

[vswr]

Sure enough. Almost five years ago.

https://www.worldwidedx.com/threads/browning-mark-3-ssb-12-volt-relay-substitute.260265/

73

Thanks. Thats definitely useful. Well, gotvtime to scope my oscillator circuits today. Nada. Now I know where to begin. Appreciate the support. 73s