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Solid state BFO in tube receiver
Noone answered this question in the Collins newsgroup, so I try it here.
I recently inspected a Collins 75S-3B receiver, and I found that someone had modified the BFO circuit with the addition of a transistor (I have not determined whether the transistor actually replaces the BFO oscillator tube, or it instead just amplifies the BFO signal). The receiver works fine, but I cannot figure out the reason for the modification. I would tend to believe that: - either it is a well known modification (but for which purpose?) - or it was just a way to circumvent the problem of a weak BFO crystal that does not start oscillating with the BFO tube alone. As BFO crystals are not easy to find, that could be a possible justification. Thanks in advance for any suggestion. 73 Tony I0JX |
#2
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Solid state BFO in tube receiver
Back in the 70s Howard Sartori had an article published in QST concerning
Solid State tube replacements. He developed a line of "tubsters" for Drake gear and later did some for Collins gear. You may just have one of his in the rig or one someone built from a construction article. Dick K8WHA __________________________ "Antonio Vernucci" wrote in message ... Noone answered this question in the Collins newsgroup, so I try it here. I recently inspected a Collins 75S-3B receiver, and I found that someone had modified the BFO circuit with the addition of a transistor (I have not determined whether the transistor actually replaces the BFO oscillator tube, or it instead just amplifies the BFO signal). The receiver works fine, but I cannot figure out the reason for the modification. I would tend to believe that: - either it is a well known modification (but for which purpose?) - or it was just a way to circumvent the problem of a weak BFO crystal that does not start oscillating with the BFO tube alone. As BFO crystals are not easy to find, that could be a possible justification. Thanks in advance for any suggestion. 73 Tony I0JX |
#3
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Solid state BFO in tube receiver
Hi, Tony
It could be that someone added an emitter follower to the receiver BFO circuit, in order to bring the BFO signal to the transmitter via coax. A drawback to the S/Line is that the transmitter BFO crystal can be different in frequency than the receiver BFO crystal due to manufacturing tolerances, making exact zero-beating difficult in transceive mode. 73, Ed Knobloch Antonio Vernucci wrote: Noone answered this question in the Collins newsgroup, so I try it here. I recently inspected a Collins 75S-3B receiver, and I found that someone had modified the BFO circuit with the addition of a transistor (I have not determined whether the transistor actually replaces the BFO oscillator tube, or it instead just amplifies the BFO signal). The receiver works fine, but I cannot figure out the reason for the modification. I would tend to believe that: - either it is a well known modification (but for which purpose?) - or it was just a way to circumvent the problem of a weak BFO crystal that does not start oscillating with the BFO tube alone. As BFO crystals are not easy to find, that could be a possible justification. Thanks in advance for any suggestion. 73 Tony I0JX |
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