I have a Tram 201A and when on LSB or USB it has a high deadkey and modulation light does not blink but stays bright and modulation not working right. I have tried other microphones and no difference. Any idea's please. Also has a hum thru speaker on sideband but not AM.
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Tram 201A high deadkey no modulation on SSB
- Thread starter Jimbo165
- Start date
Someone has twisted the adjustment screw on the neutralizing capacitor C706.
This is a square white-ceramic body part bolted to the underside of the chassis, about an inch square. It's between the driver and final tubes. Has "304M" printed on one side.
Its purpose is to cancel out the unwanted RF feedback that takes place inside the final tube.
But the adjustment is a bit finicky. What usually happens is that someone twists the adjustment screw while watching the wattmeter, hoping for just a little more on the meter.
This will totally disrupt that neutralizing circuit, and cause the final tube to become an oscillator on sideband transmit. The frequency that it now sends out to the antenna is not anywhere near the channel that's selected. If you had a frequency counter in line with the coax, you would see an unstable reading, probably around 28 MHz.
Simple fix is to simply crank that adjustment screw tighter. Odds are that it's fairly loose now.
Any time you adust C706 you will also have to peak the Plate Tune on the rear panel, and the driver coil T700. Any change to the setting of C706 will move the peak setting of those two adjustments, and require you to repeak them.
I'll skip the full adjustment procedure for C706 for now. If simply tightening it stops the SSB carrier problem, that's worth trying first.
Just be sure to re-peak T700 and the Plate Tune control on the rear panel any time the setting of C706 is changed.
Oh, and the hum on SSB receive may be from the 14-Volt DC power that comes from the plug-in "BA" board next to the audio tube. The filter capacitors on that board will certainly be bad if they are original.
Might be from a bad tube.
73
This is a square white-ceramic body part bolted to the underside of the chassis, about an inch square. It's between the driver and final tubes. Has "304M" printed on one side.
Its purpose is to cancel out the unwanted RF feedback that takes place inside the final tube.
But the adjustment is a bit finicky. What usually happens is that someone twists the adjustment screw while watching the wattmeter, hoping for just a little more on the meter.
This will totally disrupt that neutralizing circuit, and cause the final tube to become an oscillator on sideband transmit. The frequency that it now sends out to the antenna is not anywhere near the channel that's selected. If you had a frequency counter in line with the coax, you would see an unstable reading, probably around 28 MHz.
Simple fix is to simply crank that adjustment screw tighter. Odds are that it's fairly loose now.
Any time you adust C706 you will also have to peak the Plate Tune on the rear panel, and the driver coil T700. Any change to the setting of C706 will move the peak setting of those two adjustments, and require you to repeak them.
I'll skip the full adjustment procedure for C706 for now. If simply tightening it stops the SSB carrier problem, that's worth trying first.
Just be sure to re-peak T700 and the Plate Tune control on the rear panel any time the setting of C706 is changed.
Oh, and the hum on SSB receive may be from the 14-Volt DC power that comes from the plug-in "BA" board next to the audio tube. The filter capacitors on that board will certainly be bad if they are original.
Might be from a bad tube.
73
C706 took just a haft turn to tighten it up and no change dang it so not the problem . Will start some more research .
One thing I should have suggested was to pull out the 6GH8 mike-amplifier tube V600. This will eliminate any "hum" from the mike amplifier causing what LOOKS like a carrier, but is actually modulation.
If that doesn't change the picture, the neutralization is the next thing to try.
I guess I should have explained the "By Gum and By Gosh" method of setting C706 in more detail.
First, tune the radio for max MODULATED power on AM, going back and forth between the Tune and Load until no improvement is seen. Make sure T700 is peaked for modulated power.
Now, switch to SSB, turn down the mike gain and key the mike. Turn C706 either way to see if the SSB carrier goes away. There should be a position on this adjustment that causes the carrier to drop out. Unkey and then key the mike again to see if it comes back.
Next you peak T700, the Tune and Load controls for max AM modulated power. Turning C706 nearly always disturbs the previous setting of those three adjustments.
Now try SSB. You may still have that carrirer but it will be weaker. Lather, rinse repeat, following the same steps as before will get you zeroed in unless there is some additional problem beyond proper adjustment alone.
Something could be broke.
If that doesn't change the picture, the neutralization is the next thing to try.
I guess I should have explained the "By Gum and By Gosh" method of setting C706 in more detail.
First, tune the radio for max MODULATED power on AM, going back and forth between the Tune and Load until no improvement is seen. Make sure T700 is peaked for modulated power.
Now, switch to SSB, turn down the mike gain and key the mike. Turn C706 either way to see if the SSB carrier goes away. There should be a position on this adjustment that causes the carrier to drop out. Unkey and then key the mike again to see if it comes back.
Next you peak T700, the Tune and Load controls for max AM modulated power. Turning C706 nearly always disturbs the previous setting of those three adjustments.
Now try SSB. You may still have that carrirer but it will be weaker. Lather, rinse repeat, following the same steps as before will get you zeroed in unless there is some additional problem beyond proper adjustment alone.
Something could be broke.