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looking for parts for a jb12 amp need the keying circut
- Thread starter skipshooter205
- Start date
amp
i would but im trying to save for an hf radio but ill keep it in mind thanks for the reply i may just get somone to rebuild the one i have ?
i would but im trying to save for an hf radio but ill keep it in mind thanks for the reply i may just get somone to rebuild the one i have ?
K
kc2jgl
Guest
That board has two rectifiers and two filter caps to double the 6.3-Volt heater AC to around 16 Volts to key a 12-Volt relay. Also has the carrier-sensing transistor, and the parts that wrapped around it.
The only place you'll find it is in a junked amplifier. The vast majority of JB-12s sold were the older one with a 6AQ5 tube and the 110-Volt DC version of the relay. Most junkers will be the older version, with no 12-Volt board in them. And no 12-Volt relay, either.
Sounds like the kind of thing that would be easier to arrange on a piece of Rat-Shack perf board. For the keying-circuit part, we use a PNP TO-220 darlington transistor with the diodes and chatter cap soldered to the base and emitter leads. Bolting the collector tab to a grounded screw takes care of that side of the circuit. One wire goes from it to the relay, and a disc capacitor in series with a resistor strings from it to the 'radio' socket for the sensing input.
Checked my junk JB pile, and none with boards. All of them are the old version.
Perf-boarding the voltage doubler, and a keying circuit is doable. Finding that board may take a lot of looking under rocks.
I can't resist asking. Once you get the missing board (or equivalent) installed, what are the chances that the contacts on the relay are okay?
Sure would be a bummer to go to all that trouble and find out that the standby-side contacts are intermittent on the relay. The 12-Volt version is almost as hard to find as the 110-Volt DC relay that goes with older tube-type keying circuit.
73
The only place you'll find it is in a junked amplifier. The vast majority of JB-12s sold were the older one with a 6AQ5 tube and the 110-Volt DC version of the relay. Most junkers will be the older version, with no 12-Volt board in them. And no 12-Volt relay, either.
Sounds like the kind of thing that would be easier to arrange on a piece of Rat-Shack perf board. For the keying-circuit part, we use a PNP TO-220 darlington transistor with the diodes and chatter cap soldered to the base and emitter leads. Bolting the collector tab to a grounded screw takes care of that side of the circuit. One wire goes from it to the relay, and a disc capacitor in series with a resistor strings from it to the 'radio' socket for the sensing input.
Checked my junk JB pile, and none with boards. All of them are the old version.
Perf-boarding the voltage doubler, and a keying circuit is doable. Finding that board may take a lot of looking under rocks.
I can't resist asking. Once you get the missing board (or equivalent) installed, what are the chances that the contacts on the relay are okay?
Sure would be a bummer to go to all that trouble and find out that the standby-side contacts are intermittent on the relay. The 12-Volt version is almost as hard to find as the 110-Volt DC relay that goes with older tube-type keying circuit.
73
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