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D&A raider keying tube
- Thread starter Staybolt
- Start date
Pin 6 is definitely one of the two plate pins on a 12AT7/12AU7/12AX7.
That's where that relay-coil wire would go, to the plate of whatever tube is being used.
Seems to me we have an old diagram somewhere showing that kind of tube to key the relay in a Varmint amplifier. That part is crossed out with the transistor-keying circuit clearly added after the first version was drafted.
Can't remember how many decades since I last saw that type tube used for this. I'll see if I can dig up that old diagram.
73
That's where that relay-coil wire would go, to the plate of whatever tube is being used.
Seems to me we have an old diagram somewhere showing that kind of tube to key the relay in a Varmint amplifier. That part is crossed out with the transistor-keying circuit clearly added after the first version was drafted.
Can't remember how many decades since I last saw that type tube used for this. I'll see if I can dig up that old diagram.
73
One thing that can make it "buzz" when you key the radio is for the tubes to have a terribly high SWR on the input side. The Raider should have a "grid tune" adjustment screw on the rear near the radio coax socket. It serves to adjust the input impedance of the tubes to 50 ohms or something close.
If it's adjusted way wrong, this could reduce the RF voltage that activates the keying tube, making the relay drop back out.
Of course, when the relay drops back out, the high SWR goes away, and the keying tube "wakes back up" and tries to close the relay again, but only for the brief moment before the contact points feed the radio drive into the tubes and the keying tube's trigger voltage drops again.
Lather, rinse, repeat. Fifty or a hundred times a second.
Might be the whole problem. More than once I have set that 'grid tune' for minimum buzz from the relay.
Must be getting old. Didn't think of that first time around.
73
If it's adjusted way wrong, this could reduce the RF voltage that activates the keying tube, making the relay drop back out.
Of course, when the relay drops back out, the high SWR goes away, and the keying tube "wakes back up" and tries to close the relay again, but only for the brief moment before the contact points feed the radio drive into the tubes and the keying tube's trigger voltage drops again.
Lather, rinse, repeat. Fifty or a hundred times a second.
Might be the whole problem. More than once I have set that 'grid tune' for minimum buzz from the relay.
Must be getting old. Didn't think of that first time around.
73
