Mark III transmitter problem

[48423mike]

I have a mark III that worked perfect until the other day, the transmit power was down a little so I adjusted it on the back of the radio. Now its stuck on just one freq. 26.880 and it doesn't even have the lowers in it its stock, Check the crystal output and its good on all of them. you can pull out the 12by7,6cb6,6gh8 and the radio still keys and trans on 26.880 I did notice that if you turn the pot on the back to adjust power the freq changes. anybody got any clues I m lost on this one. Thanks mike

[Night Crawler]

the transmit power was down a little so I adjusted it on the back of the radio. Now its stuck on just one freq. 26.880 you can pull out the 12by7,6cb6,6gh8 and the radio still keys and trans on 26.880

Seems like the final is self oscillating what did you adjust?

There is a adjustable neutralization cap C23 that's used to prevent self oscillation if that was turn by mistake that could be your problem..

[48423mike]

Thanks night crawler I will check that out. we only adjusted the back out put screw but who knows. thanks again I'll let you know what happens. mike

[Night Crawler]

we only adjusted the back out put screw but who knows.

That transmitter uses fixed loading with only one adjustment for rf output the one you adjusted on the back is the Plate tuning capacitor C26 if that is adjusted it could effect the adjustment on C23 the neutralization cap since they interact.

Now its stuck on just one freq. 26.880 you can pull out the 12by7,6cb6,6gh8 and the radio still keys and trans on 26.880 I did notice that if you turn the pot on the back to adjust power the freq changes.

Those are all the signs of self oscillation try adjusting C23 the neutralization cap that should stabilize the final.
C23 should be inside the transmitter connected to C26 the plate adjust cap which both go to pin 6 of the 7558 final.

Be careful when adjusting C23 and C26 as there's a 250 vdc potential on them.

[48423mike]

Hay night crawler had to replace c-23 with a 3 pf cap but works great. The watts are right back where they should be all across the band and right on freq. Thank You Very much for the info. Mike

[Dirty Diaper]

I see someone has a Browning Golden Eagle Mark111. That is great!My friend and I have several sets, and are having trouble with some of them .One is keying up @10-swinging to@18 watts. This radio has been altered with a switch across the big resistor to the 7558 final tube. Even with the switch in the low position, the key is still @8 watts. We need to get this back down to the 3 watt range. Is there a fix to this, and is there a modification, other than adjusting Vr38, or what ever the number is for the modulation, to increase the modulation ? Any tips, advice will be helpful. Just trying to keep these @36 year old rigs a-goin.

[Night Crawler]

My friend and I have several sets, and are having trouble with some of them .One is keying up @10-swinging to@18 watts. This radio has been altered with a switch across the big resistor to the 7558 final tube. Even with the switch in the low position, the key is still @8 watts. We need to get this back down to the 3 watt range. Is there a fix to this

What was done with the switch was to jump the resistor going to the screen grid of the final not a good thing to do.
Remove the wires and the resistor (the value might of been changed with that modification) replace that resistor with a 15K two watt resistor that will put the transmitter back to stock.

is there a modification, other than adjusting Vr38, or what ever the number is for the modulation, to increase the modulation ?

Remove R35 a 47k resistor going to pin 1 on the microphone jack in the transmitter and replace it with a 100uh choke available at radio shack.

What also could be done is to increase the value of the interstage coupling capacitors in the audio amplifier stages then remove V8 the 12AU7 clipper and L6 filter and couple the audio directly from the plate of V7 the 12AX7 speech amp to the grid of V9 the 6BQ5 modulator.

[Dirty Diaper]

Thanks a lot, the info you have given is valued highly.I will check the resistor at the final, and like you suggested, remove the switch. The Major modification for the modulation, will have to proceed slowly. I will have to have help with a sketch of the revised circuit, and values for the components first. I will study the Sams schematic real closely. J.T.

[Lik2race]

Nightcrawler I too also want to say THANK YOU.. Dirty Diaper & I are best of friends, and he is talking about my Mark III ( Or I should say -ONE of my Mark III's ). Now I think it can be fixed.
Thanks again..
Stan

[Dirty Diaper]

Hey ilike2race-- Can you bump it down on 27.105 later. I want to check out the Mark111, and get you to tell me about the great idea of the different lights for the receivers mode switch. DD :r&r: And another thing- What did happen to Big Hair Radio Man?

[Dirty Diaper]

Break 12, for Bad Habit- Hey- Ilike2race--where have you been--no info on Big Hair Electronics -I am also trying to contact The Tram Dr. (the one on you-tube), do you know his E-mail- or how I can contact him? Let me know 10-4. DD

[HOUND DOG]

Does anyone know of a good shop that repairs Browning Mark III's?

[warlock35po]

Greg Barkett of Barkett Electronics on the web,or Fixer on this forum i believe,both top notch. Regards warlock35po

[warlock35po]

I willtry again read the first two words backwards ttekraB scinortcele Greg on the web Regards warlock35po

[Dirty Diaper]

I am looking in a hand mirror, and have broken the code! Thanks----

[Night Crawler]

I willtry again read the first two words backwards ttekraB scinortcele Greg on the web Regards warlock35po

I am looking in a hand mirror, and have broken the code! Thanks----

[Dirty Diaper]

Hey Like2race-- call me sometime on CH12--- Hope to hear that aw---sume new set of MarkIII's again. I sent SCUBA a PM in Elkin N.C., what day did you say you were going there? Do I need to bring my fold up hand truck for that big amp? Let me know--- D.D..

[Stingray]

My friend and I have several sets, and are having trouble with some of them .One is keying up @10-swinging to@18 watts. This radio has been altered with a switch across the big resistor to the 7558 final tube. Even with the switch in the low position, the key is still @8 watts. We need to get this back down to the 3 watt range. Is there a fix to this

What was done with the switch was to jump the resistor going to the screen grid of the final not a good thing to do.
Remove the wires and the resistor (the value might of been changed with that modification) replace that resistor with a 15K two watt resistor that will put the transmitter back to stock.

is there a modification, other than adjusting Vr38, or what ever the number is for the modulation, to increase the modulation ?

Remove R35 a 47k resistor going to pin 1 on the microphone jack in the transmitter and replace it with a 100uh choke available at radio shack.

What also could be done is to increase the value of the interstage coupling capacitors in the audio amplifier stages then remove V8 the 12AU7 clipper and L6 filter and couple the audio directly from the plate of V7 the 12AX7 speech amp to the grid of V9 the 6BQ5 modulator.

How does the 100uh choke improve modulation?

[warlock35po]

Hello, Update On Greg Barkett,i spoke to him last week he is no longer in the repair business sounded like only parts.He will Really be missed.Anyone know of another Rupturable repair service to work on these old Dinosaur,to keep the Dream alive? Regards,Warlock 35po

[Trapper267]

Look up Matt Bee on Face Book. He's in FL. I can forward his number to call if you want it, Warlock