Need help! Browning Mark III catastrophie!

[crazy_cooter]

Hey guys, I need some help! My Browning Mark III just finally started showing its age today and let me down! Earlier, I was sitting beside it here on my computer and all the sudden I hear the radio "click". I looked over, and the radio is keyed up all by itself! I thought something in the mic shorted out, so I unhooked the mic and it unkeyed. I run a non-amplified d-104 on it, so i tore it down, and couldnt find anything wrong with it. The contacts are working good, and clean. No wires are touching, and nothing i see can be wrong with this mic. I took another mic, a silver eagle, and hooked it up and the radio works fine. I tried the banana mic, and the radio makes a buzzing noise internally when its keyed up. I have been working on this radio since noon, and its 5:30 now. I'm lost for ideas! Anyone know what to do? I'm up for suggestion

[crazy_cooter]

any suggestions?

[crazy_cooter]

Just a little more info, the radio keys up and has good power with the factory banana mike, but has a humming noise in the transmitter when keyed. It is not the relays, and I cannot test my tubes at this time due to my tube tester not working properly. It has nothing at all to do with the microphone, it is something internal in the transmitter. Could it be an audio driver tube shorted out?

[Night Crawler]

Could it be an audio driver tube shorted out?

Is there no audio on transmit or just a hum with the audio?
If there is no audio a tube would be suspect.

The radio keys up and has good power with the factory banana mike, but has a humming noise in the transmitter when keyed.

If your getting proper power output but a hum with the audio I would check the 40uf HV filter capacitors C61A,B and C also C62 and also check the HV rectifiers SR-2 and SR-3 used in the voltage doulbler for the high voltage.

[crazy_cooter]

hey thanks for the input. I was beginning to wonder if i'd get any hits on this topic. I haven't tried to modulate the radio, but the hum is in the audio too. I was kinda suspicious of some of the filter caps being bad. I recapped the reciever but not the transmitter. I will check those out soon after i send this message. Thanks!

[Night Crawler]

You can make a big improvement in the fidelity of the audio by eliminating the 12AU7 clipper also the L6 filter and changing the audio interstage coupling caps to a higher value when you get it working.

[crazy_cooter]

ok night crawler, I appreciate the input tremendously. I have the bottom cover off and a schematic in hand. I'm gonna go through it with a fine tooth comb

[crazy_cooter]

It appears that the C62 capacitor has been changed, but has the wrong value. It's supposed to be a 40 mfd, and it has a 33 uf cap in its place. I dont think its hurting anything though.

[Night Crawler]

No, 33uf is enough filtering but check all them with a multimeter to see if they're good also check the voltages off the voltage doubler during transmit shown on the schematic and see if they correspond.

Check the rectifiers with a multimeter also.
If one of the rectifiers SR-2 or SR-3 is open or shorted instead of acting like a fullwave doubler it will act like a halfwave rectifier circuit and that will definitely cause a hum during transmit.

If everything checks out ok the problem is somewhere else in the circuit.

[crazy_cooter]

Let the good times roll!! Im gonna be up all night long!
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[Night Crawler]

You gotta do what you gotta do
By the way that radio is in really nice shape.

[crazy_cooter]

Thanks, I couldn't resist I had to take a break and snap some shots of the inside of the receiver. Look how clean it is.....
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[Night Crawler]

It looks almost new I just noticed the Nuvistor tubes in the back of the chassis at one time they were state of the art technology.

[crazy_cooter]

its amazing how technology has evolved isnt it?

[Nagant]

They are in really nice condition. Hope you get it figured out soon. Regardless of what the issue turns out to be I would replace all the electrolytic capacitors in the transmitter if you haven't already.

I run some of those Nuvistor front end radios well.

[crazy_cooter]

The good news is my transmitter recap job was successful. The bad news is, I still didnt fix the problem. Nor have I been able to find the problem. This ones a dandy!

[crazy_cooter]

They are in really nice condition. Hope you get it figured out soon. Regardless of what the issue turns out to be I would replace all the electrolytic capacitors in the transmitter if you haven't already.

I run some of those Nuvistor front end radios well.

What kind do you have?

[Nagant]

Some of the Lafayette HB series radios and a USL Contact 8.

[crazy_cooter]

I like Lafayette, they made a nice radio

[Nagant]

Yes me too. I have quite a few Lafayette tube rigs. My favorite is my Lafayette HB-444/25B.


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[crazy_cooter]

oh nice! I like that! I can't remember the one I had a long time ago. It was silver faced and looked like a galaxy saturn or excalibur base. I cannot remember what model it was for the life of me.

[Nagant]

There was a Lafayette like you mentioned that was nothing but a Galaxy Melaka (AKA SSB). The Lafayette branded one seems to be uncommon though.

Here are some other Lafayette tube rigs that need my attention someday when I feel up to reviving them.



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Sorry about going so far off topic.

[crazy_cooter]

Those radios would make a great project for sure! Keep me posted if you ever decide to restore them, i'd like to see the progress. Yes, that Lafayette base I had was nothing more than a Galaxy Melaka, which I had forgotten about until you mentioned it.

[Nagant]

Will do. It takes me some time to restore radios as I have some health issues that really interfere with such things. I have a Courier and a couple of Johnson Messenger 1's ahead of the Lafayette's that I've been working on off and on lately.

[crazy_cooter]

Yeah you know what they say. All good things come in time.