SX-28 Sensitivity
 

I am restoring an old Hallicrafters SX-28 and have one remaining issue
that I need to resolve -- poor sensitivity on the upper bands, which
appears to be related to very poor signal transfer from the antenna to
the grid of the first RF amplifier tube. IF stages appear to be
functioning well. I have signal voltage readings (oscilloscope) for
all of the inputs and outputs from the antenna to the output of the
mixer, but have no baseline to which I can compare my readings.

If someone is familiar with the SX-28 and the relative signal
intensities that I should be seeing at the various RF stages, please
contact me via e-mail so that I can discuss this.

Thank you!!

SX-28 Sensitivity
 

On Mar 6, 1:40*pm, Hank wrote:
I am restoring an old Hallicrafters SX-28 and have one remaining issue
that I need to resolve -- poor sensitivity on the upper bands, which
appears to be related to very poor signal transfer from the antenna to
the grid of the first RF amplifier tube. IF stages appear to be
functioning well. *I have signal voltage readings (oscilloscope) for
all of the inputs and outputs from the antenna to the output of the
mixer, but have no baseline to which I can compare my readings.

If someone is familiar with the SX-28 and the relative signal
intensities that I should be seeing at the various RF stages, please
contact me via e-mail so that I can discuss this.

Thank you!!

Is the oscillator voltage holding up on the higher bands? Check the
self-generated oscillator tube grid bias voltage with a high-
impedance, low capacitance probe to a VTVM or DMM on DC volts range.
Compare measurement to that on the lower bands.
Cheers,
Roger

SX-28 Sensitivity
 

Is the oscillator voltage holding up on the higher bands? *Check the
self-generated oscillator tube grid bias voltage with a high-
impedance, low capacitance probe to a VTVM or DMM on DC volts range.
Compare measurement to that on the lower bands.
Cheers,
Roger
==============
That is a good suggestion. I ended up putting a 6SB7Y in the local
oscillator position in my SX-28 to get reliable operation on band 6
(21-43 Mc.). It doesn't hurt to use a 6SB7Y in the mixer position
either. Even with that, the sensitivity on band 6 is not up to the
lower bands. --Ed