I got this from a friend of my Father's the other day,and overall,it is in pretty nice shape.I went through it and replaced the handfull of plastic-encased caps(black beauties?) and replaced a couple of the electrolytics.None of the electrolytics showed any leakage on my IT-28,but the ones I replaced,read low for capacitance value.

I tested all of the tubes, and all but one tested fine.The baddy(6BJ6) actually really wasn't,it just shows a medium amount of H/K leakage,but is still useable.

The radio works pretty well and I noticed that someone did a couple of small mods to it.They replaced the rectifier tube with a solid-state module.I read on a CB forum that this was a common mod for these radios, to raise operating voltages, and gain a little output power.B+ is about 50 volts higher than spec.Also,they would either put a jumper across R48,or parallel it with another resistor,to get a voltage increase.Mine has a 2K resistor across said resistor.

Anyway,to get to the point,the radio has a hum problem that is beyond my troubleshooting skills.With the radio in the receive mode,there is hum in the background,but is not 60 Hz power supply hum.With the volume turned all the way down,it is quite noticeable and annoying.It does not seem to increase with the volume control,but would be hard to detect with the usual reception noises,even with the antenna disconnected.

If I engage the squelch,the hum disappears with the audio.I found that if I remove the 12AU7 first audio tube,the hum remains.However,if I remove the 6AW8 second audio,the noise is gone.I'll assume then that the problem is in the area of the 6AW8, or the 12AB5 output tube.

I noticed that none of the audio tubes have shields,and according to the factory service manual,never did.I tried putting shields around the pre-amp tubes and it did nothing.Don't know where to go from here.Any ideas would be greatly appreciated.

At the address below,you will find the schematic from the factory service manual.
Thanks,Mike.

http://www.cbtricks.com/radios/ef_johnson/messenger_1/graphics/messenger_1_242_127_128_sch.jpg

IPAddress: ***.22.182.245