After consulting that units schematic, some thoughts come to mind, since in actuality, a grid dipper is a grid dipper is a grid dipper. . . . aka. . . Holy Mackeral 'dere Andy. . .who do be de grid DIPPOR and who do be' de grid DIPPEE ?
Any chance that units selenium rectifier has deteriorated down in performance, such that it is producing
a lowered B+ supply level to the oscillator tube circuitry.
Check your end B+ level at either pin 7 or 1 of the 6AF4 and see how close it is to the norm of +55 VDC.
If lower, then check back thru the R3--6.8k and R4--2k dropping / filter/ isolation resistor chain to see
if those old carbon composition resistors have risen upwards in value with time.
If the B+ is lowered an equal possibility is of the C6--50 ufd and C7--10 ufd filter capacitors having
dried up and lowered the B+.
That could be detected by:
Measuring the AC ripple across them
Test shunting them with new caps
Or, if you would place the unit near a BCB radio , then plug in the proper osc / dipper coil for that frequency and then listen to the RF carrier received to see if an appreciable hum modulation is being present on the received carrier signal.
Also, do a like check out of the R2--10k grid resistor.
If all of that passes, then the next operational aspect would the manner of coupling to the test circuitry,
quite close coupling is needed in order to get any apprecable dip action, and the better the "Q " of the tested circuit. . . . the better the dip action, and the further away the osc coils placement can be.
On old low "Q" circuitry I invariably had to "kiss" the osc coil to the test coil with them being in the same
winding plane. Or, the osc coil being inserted within the hollow coil form of large units or with the osc coil
enveloping smaller coil forms within itself. . . .and then backing away to fine tune in on the progressively decreasing dip action.
Poor dip action is somewhat averted in newer solid state and FET vertions, where they can have a DC meter amplifier being utilized, and then tap the metering into a voltage divider portion of its outputs in order to sample the sole finite portion of interest in its overall voltage swing.
73's de Edd
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:After consulting that units schematic, some thoughts come to mind, since in actuality, a grid dipper is a grid dipper is a grid dipper. . . . aka. . . Holy Mackeral 'dere Andy. . .who do be de grid DIPPOR and who do be' de grid DIPPEE ?
:
:
:
:Any chance that units selenium rectifier has deteriorated down in performance, such that it is producing
:a lowered B+ supply level to the oscillator tube circuitry.
:
:
:
:Check your end B+ level at either pin 7 or 1 of the 6AF4 and see how close it is to the norm of +55 VDC.
:If lower, then check back thru the R3--6.8k and R4--2k dropping / filter/ isolation resistor chain to see
:if those old carbon composition resistors have risen upwards in value with time.
:
:
:
:If the B+ is lowered an equal possibility is of the C6--50 ufd and C7--10 ufd filter capacitors having
:dried up and lowered the B+.
: That could be detected by:
:
:Measuring the AC ripple across them
:
:Test shunting them with new caps
:
:Or, if you would place the unit near a BCB radio , then plug in the proper osc / dipper coil for that frequency and then listen to the RF carrier received to see if an appreciable hum modulation is being present on the received carrier signal.
:
:
:
:Also, do a like check out of the R2--10k grid resistor.
:
:
:
:If all of that passes, then the next operational aspect would the manner of coupling to the test circuitry,
:quite close coupling is needed in order to get any apprecable dip action, and the better the "Q " of the tested circuit. . . . the better the dip action, and the further away the osc coils placement can be.
:
:
:
:On old low "Q" circuitry I invariably had to "kiss" the osc coil to the test coil with them being in the same
:winding plane. Or, the osc coil being inserted within the hollow coil form of large units or with the osc coil
:enveloping smaller coil forms within itself. . . .and then backing away to fine tune in on the progressively decreasing dip action.
:
:
:
:Poor dip action is somewhat averted in newer solid state and FET vertions, where they can have a DC meter amplifier being utilized, and then tap the metering into a voltage divider portion of its outputs in order to sample the sole finite portion of interest in its overall voltage swing.
:
:
:
:
:
:
:73's de Edd
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