• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Mark 3 meter pegs

Van Lifeson

Well-Known Member
Aug 11, 2018
214
246
53
57
So, I have read a lot about the meter pegging with modulation on a Mark three. What causes this? I have read that it could be the mode selector switch. I have inspected mine and I do not see any signs of traces, such as the carbon deposits people talk about. Doesn’t mean they are not there, but I don’t believe this radio was used very much and the switch looks to be in very good condition. But, my needle does peg violently when I have the switch set to modulation. Why does this do this?
Thanks
 

First thought is that the transmitter is improperly aligned.(I.e.-Too much mike gain)

If you mean it stays stuck in the extreme RH corner even during receive, some voltage measurements are in order.

73
David
 
Usually it's the mode switch that starts to break down that causes your problem. Do NOT use any kind of cleaner on it. I have also seen the 7558 tube not working correctly with the modulator circuit that pegs the needle hard. If you say your mode switch is ok, then try another final tube and see if it rectifies the problem. Just re-adjust your bias in ssb mode and peak your radio for max rf out on your wattmeter. Good luck
-Trainman
 
  • Like
Reactions: tecnicoloco
If it only pegs when you talk, that's normal. Apparently Browning wanted you to turn down the internal mike gain to the 100% level.

If it pegs while receiving, that's bad juju. Can burn out the coil in the meter. When the first circuits in the selector are breaking down you'll generally find that the resistor pointed out below looks overheated or just burned.

r51sortadetailwu1.jpg


There are two kinds of Mark 3 SSB transmitters: Ones that have had a breakdown in the mode selector, and the rest of them that will.

Just have to run it long enough. A radio with 500 original miles will take longer for the selector to break down than a high-mileage unit. But it's not a question of if, it's a question of when.

Gotta get organized and post the 'cheap' solution, hot-wiring the radio for AM only, taking the failed selector out of the circuits.

73
 
That would be great. An easy solution to make it AM only would be awesome.
Take the worry out of it blowing up LOL.
 
If it only pegs when you talk, that's normal. Apparently Browning wanted you to turn down the internal mike gain to the 100% level.

If it pegs while receiving, that's bad juju. Can burn out the coil in the meter. When the first circuits in the selector are breaking down you'll generally find that the resistor pointed out below looks overheated or just burned.

r51sortadetailwu1.jpg


There are two kinds of Mark 3 SSB transmitters: Ones that have had a breakdown in the mode selector, and the rest of them that will.

Just have to run it long enough. A radio with 500 original miles will take longer for the selector to break down than a high-mileage unit. But it's not a question of if, it's a question of when.

Gotta get organized and post the 'cheap' solution, hot-wiring the radio for AM only, taking the failed selector out of the circuits.

73
Any idea why someone would put another 250 ohm in parallel with the one you show?
That’s what I have. What would this do? Should I remove it?
 
The original single resistor is there for filtering the rectifier ripple. It also causes some drop in the B+ voltage to the audio and RF power stages. Adding a resistor in parallel reduces the resistance in the power supply circuit, and raises the voltage supplied to the tubes.

Makes the wattmeter read higher. Does reduce supply filtering a bit, but probably not enough to tell. When a customer just wants to see more wattage from this model, we double the capacitance of the main filter capacitors. This allows us to use a resistor in that spot with a lower resistance, and get the same effect as simply soldering a second parallel resistor to the original one.

You'll see the carrier power fall a bit if you remove the extra resistor, and a bit less peak power on modulation.

73
 
The original single resistor is there for filtering the rectifier ripple. It also causes some drop in the B+ voltage to the audio and RF power stages. Adding a resistor in parallel reduces the resistance in the power supply circuit, and raises the voltage supplied to the tubes.

Makes the wattmeter read higher. Does reduce supply filtering a bit, but probably not enough to tell. When a customer just wants to see more wattage from this model, we double the capacitance of the main filter capacitors. This allows us to use a resistor in that spot with a lower resistance, and get the same effect as simply soldering a second parallel resistor to the original one.

You'll see the carrier power fall a bit if you remove the extra resistor, and a bit less peak power on modulation.

73
Besides removing the resistor in parallel,
What else can be done to lower the dead key
On a mark 3?
 

dxChat
Help Users
  • No one is chatting at the moment.
  • dxBot:
    Tucker442 has left the room.
  • @ BJ radionut:
    LIVE 10:00 AM EST :cool:
  • @ Charles Edwards:
    I'm looking for factory settings 1 through 59 for a AT 5555 n2 or AT500 M2 I only wrote down half the values feel like a idiot I need help will be appreciated