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JB 2000 transformer
- Thread starter 238
- Start date
Better to ground the shield of the fat output coax at the frame of the Load control, and at the ground screws on the "antenna" connector.
Both ends, as close to the source (or destination) of the center conductor's current as you can.
Tends to improve stability.
73
Both ends, as close to the source (or destination) of the center conductor's current as you can.
Tends to improve stability.
73
In the pic you can see black & blue wire soldered together at the relay. The blue wire goes to the stud mounted diode. The black wire goes to a switch on the front that is marked AM/AM+. On AM the switch is open & on AM+ it grounds the diode. AM+ gives it more watts. What is the purpose of this deal and it a good thing? 238
The stud-mounted diode is a zener diode. It holds a constant bias voltage on the tube, reducing the current the tube will draw with no drive. This also reduces the heat the tube will produce from the AM carrier.
You'll see more average power with the switch closed, shorting across the zener. The tube will run at a higher temperature this way.
A peak-reading meter will usually read higher in "AM" mode, especially if you set the Load control for max modulated power, and NOT just on a dead carrier.
The tube tends to last longer at the reduced operating temperature.
73
You'll see more average power with the switch closed, shorting across the zener. The tube will run at a higher temperature this way.
A peak-reading meter will usually read higher in "AM" mode, especially if you set the Load control for max modulated power, and NOT just on a dead carrier.
The tube tends to last longer at the reduced operating temperature.
73
Just noticed the aluminum pop rivets holding your coax sockets to the rear panel. If they are tight, they may be okay. But if either one reveals ANY looseness at all, those rivets need to be drilled out and replaced with machine screws. A tooth washer under the nut serves to pierce through the surface oxide of an aluminum panel and provide a proper ground for the coax sockets.
Might be relevant, might not.
We routinely ground the coax braid to one screw of the coax socket with a ground lug.
73
Might be relevant, might not.
We routinely ground the coax braid to one screw of the coax socket with a ground lug.
73
BJ radionut You ask about the tank coil so i took a better pic. ( Does the picture also seem to show the output coax attached to the end of the tank coil (?) maybe a P-L net)
The tank coil is tied to a stand off & A wire runs from the load tuner too the stand off. The coax is solder between the stand off & the coil. It is all working ok, except the load has to be open to have modulation. Move it either way you lose your modulation. Using my Cobra 200 15 watt dead key. Amp keys 50 swings 250 on my Siltronix 600 average meter. 238
The tank coil is tied to a stand off & A wire runs from the load tuner too the stand off. The coax is solder between the stand off & the coil. It is all working ok, except the load has to be open to have modulation. Move it either way you lose your modulation. Using my Cobra 200 15 watt dead key. Amp keys 50 swings 250 on my Siltronix 600 average meter. 238Got a ? about the door knob caps The one on the tune is a 1000 pf , but reads 880 pf & the one on the load is a 100pf an reads 107pf. Do i need to change the one on the tune out or is 880pf close enough? I have been running the amp works ok, just wondering about the caps. 238
Good chance that the 1000pf part was rated only for a +/- 20% tolerance.
If so, the permissible range of measured value would be from 800pf to 1200 pf. Makes the 820 pf reading a "good" test.
73
If so, the permissible range of measured value would be from 800pf to 1200 pf. Makes the 820 pf reading a "good" test.
73
