[Hallicrafters] R-274 Dial Calibration

[Richard Knoppow]

      The spec is 0.2%. One cause can be the centering of the 
plates of the tuning capacitor. I don't know how the capacitor of 
the R-274 is made but most variable air caps have a bearing 
adjustment which will affect the centering of the rotor in the 
stators. If not centered the capacitance "law" will not be 
correct. Also, if the stators are not fixed they may be off 
center. In the SP-600 version of this receiver the stators are 
held in place with clamps consisting of screws and fiber washers. 
They can drift off with time and throw off the dial calibration 
and RF tracking. If the rotor bearing is not correctly it will 
shift the rotor over a little, enough to affect calibration. A 
visual inspection may show this but if the error is small you 
will have to use feeler gauges to check the centering.
    A mechanical error will affect all bands. If the error is on 
one band or a couple of bands it may be due to drifted padding 
capacitors in the oscillator circuit. Padders are not always 
used, the circuit diagram will tell you. I have had to replace a 
couple in the SP-600 but the Hallicrafters version may be different.
    If all bands are off its the tuning cap. I hope no one has 
gotten into it and bent plates.

On 2/16/2018 6:34 AM, Thomas Hoyer wrote:
> Going through the calibration on my R-274. I can get the dial end points spot on but once you tune past the calibration points, the dial accuracy goes to pot. For example on Band 1 when cal the end points but the mid point is off by at least 10khz.
> 
> 
> I know enough to not expect the dial accuracy to be spot on everywhere, but is there a way to improve on the results I'm seeing?
> 
> 
> Thanks.
> 
> 
> Tom
> W3TA


-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL