Does anyone have any information on modifications, upgrades, etc., to this radio?
Thanks!
Jeff S.
http://bama.sbc.edu/hallicra.htm
Dave
Next question: There's a shielded wire that connects to the C18/C19 junction at one end (by the variable choke next to the 76 tube). The other end is disconnected, obviously from the 6SQ7G. I'm guessing it should be connected to the 6SQ7G grid--but that's just it, I'm guessing. This particular connection isn't on the schematic anywhere, but since this circuit has an impact on the pitch when the BFO is energized, it must be connected into the audio circuit somewhere.
Can anyone confirm or correct my guess?
Thanks,
Jeff
:There are two versions of this radio, you have the later version. Check here for the correct schematic.
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:http://bama.sbc.edu/hallicra.htm
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:Dave
Elusively sneaking in…… under the “anyone” category.
Initially.....I’m blind…can’t see a thing.
……Assuming that unit being old enough to probably be using cotton wiring with your positively tracking down its routing to be in the 6SQ7 area, I can fill in on some possibilities.
I cant see the degree of “tightness of coupling” into the BFO oscillator circuit but what is typically being done is the extraction of a bit of the continuous RF signal from the slightly adjustable, coincident IF frequency of the receiver and its being coupled over to a later stage in the IF string. At that point, it will heterodyne with the IF signal and produce an audio tone to be further amplified for the receiving of code or a precise upper /lower tone shift to an RTTY converter.
It can even provide a referencing note (zero beat) for exacting tuning onto a received station, IF the unit has been previously zero beat against a precise frequency standard, such as WWV.
The usual procedure I see Hallicrafters using on my newer receivers is to have fed the signal via the shielded line from its having initially taken a sample of the BFO osc signal and then route it up to the first grid of the last IF amplifier of the set. That is where they then take the ends insulated wire and close wind a few INSULATED turns around that 1st grids wiring right beside the tube pin connection. That provides a “gimmick” capacitive coupling of low pf value in accordance to the used wire area and dielectric constant of the insulation.
That provides a proper balance of the two levels, as they are then going to then receive quite heavy mixed amplification in that IF tubes stage before hitting the output transformer and its detection.
IF injected further down… e.g....at the output winding of the IF transformer…. a much higher sampling level of BFO RF would be required.
Those are my findings….will wait to see if you find any concrete evidence of the injection point having been at any other point, than which I mentioned.
73's de Edd
You hit the nail on the head. A few turns of the insulated wire were wrapped around the wiring. After I replaced one of the caps in the pitch switch and turned the BFO on, I got an adjustable tone. It doesn't work well unless without the shielded wire being wrapped.
Thanks a heap!
Jeff S.
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:Elusively sneaking in…… under the “anyone” category.
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:Initially.....I’m blind…can’t see a thing.
:……Assuming that unit being old enough to probably be using cotton wiring with your positively tracking down its routing to be in the 6SQ7 area, I can fill in on some possibilities.
:
:I cant see the degree of “tightness of coupling” into the BFO oscillator circuit but what is typically being done is the extraction of a bit of the continuous RF signal from the slightly adjustable, coincident IF frequency of the receiver and its being coupled over to a later stage in the IF string. At that point, it will heterodyne with the IF signal and produce an audio tone to be further amplified for the receiving of code or a precise upper /lower tone shift to an RTTY converter.
:
:It can even provide a referencing note (zero beat) for exacting tuning onto a received station, IF the unit has been previously zero beat against a precise frequency standard, such as WWV.
:
:
:The usual procedure I see Hallicrafters using on my newer receivers is to have fed the signal via the shielded line from its having initially taken a sample of the BFO osc signal and then route it up to the first grid of the last IF amplifier of the set. That is where they then take the ends insulated wire and close wind a few INSULATED turns around that 1st grids wiring right beside the tube pin connection. That provides a “gimmick” capacitive coupling of low pf value in accordance to the used wire area and dielectric constant of the insulation.
:That provides a proper balance of the two levels, as they are then going to then receive quite heavy mixed amplification in that IF tubes stage before hitting the output transformer and its detection.
:
:
: IF injected further down… e.g....at the output winding of the IF transformer…. a much higher sampling level of BFO RF would be required.
:
:Those are my findings….will wait to see if you find any concrete evidence of the injection point having been at any other point, than which I mentioned.
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:73's de Edd
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