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Antique Radio Technical Forum
Eico 710 Grid Dip Meter

Posted by Bob Z on 04/04/2009 17:57

Sir Edd.
Filter's are ok, no loose connections, but overall construction was not the best, in fact rather sloppy. I believe this is where the trouble stems from. This thing is a nightmare to work ok, so it will stay as is until a snow storm next winter.
Thanks for the help.
Bob

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: At 780kc on the grid dip comes in at 710 on a radio.
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:In that case then you are needing less inductance in the circuit , so rotating the slug outwards from the center of the coils plexus, with a non metallic alignment tool, should raise that frequency, for the correction which you are needing.
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:Check the purity of the DC on the instrument as per the health of the 60 and 10 ufd filters.
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:As per the abberations on the wave form. . . . .thats no rock steady osc ckt. . . . .take a finger nail and firmly tap on the case the of the unit and its result on the scopes response !
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:73's de Edd

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:::Sir Bob. . .Z ( and that's very HEAVY on the ZZZZeeeeeeeeeee)
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::: I had the HEATH kit version initially and later upgraded to the Millen and then a Barker Williamson. The only complaint with the HEATH was the eccentricity of its clear Lucite frequency dial which rubbed the inside of the case and eventually made it “frosted”.
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:::Thereby, making it VEWY hard to read out the freq dials numbering.
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:::Calibration. . . .calibration. . .WHUT CALIBRATION ?
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:::I never considered a Grid Dipper to even BE in the “CALIBRATED” instrument category. I was always just dipping L/C combos
:::for establishing their values or else their estimated frequency of resonance.
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:::So I am wondering, is what spectrum hackles you the most on its accuracy?. . . .or requirement. . .since you can’t even
:::establish a whole lot of accuracy in setting a little 2.5---3 inch plastic dial disc thru 180 degrees.
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:::Without anyof your feed back yet on the freq range(s), I can only say that any correction to the dial logging that is
:::permanently printed up, will have to be established with the variance of the one transportable element. . . . which would be
:::the coil assembly for that particular band of interest. . . .as the capacitor proper is not a variant from freq segment to freq
:::segment.
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:::Say, lets hypothetically take the 700-1380 Khz coil assembly with its mid band being ~1050 Khz. Now if we place the unit up near a radio and have the dipper dial tuned “RAT ON” that 1050 Khz setting and hear that carrier coming in and being received at a known 1100 Khz on the radio then that bands plug in inductor needs to be of a GREATER inductive value to skew the output frequency downwards in order to be in coincidence with the dial calibration.
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:::Hey that’s bad news. . . .wanna’ rewind that coil with an extra turn or two or three or four on each end of it ?
:::But the alternate corrective manner to TRY, is to place a decade or so of capacitance across the ends of the coil inside the bottom of the plug in coil form, that being done in the form of a small variable ceramic or mica trimmer capacitor. Then one can test the freq shift that is acquired with that trimmer cap at its max value and its min value to see if the correct degree of freq correction can be acquired in order to then establish mid band calibration. Then you adjust trimmer slowly and then. . . . .Heyyyy. . .1050 Khz is 1050Khz, but we will have to now let the high end and low end fall in as they may .
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:::The other possibility to have been encountered, was for that 1050Khz on the dipper dial to have been received at . . .say. . 1000Khz on the radio dial. Now in that case, one need less inductance on that coil form.
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:::That can be accomplished via the taking off equal portions of a turn from both ends. Dropping the inductance skews the frequency upward in order to raise that 1000Khz on upwards, to eventually coincidence with that required dipper dials 1050 mark.
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:::4 holes, offset 90 degrees, around the ends of the windings , on both ends of the coil form windings, will let one take off ¼ of a turn at a time and pass thru its adjunct hole to go down to the connector plugs at the bottom of the coil form.
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:::Keep decreasing with the the ¼’s of a turn removed until calibration is met.(If you boo-boo and over do it there is always the trimmer trick above, to correct !
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:::Same procedure for any other bands coils that need correction. (Excepting that copper or aluminninnyumyum "horse shoe" that is used on the 100-250 Meggling-Hurts band.)
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:::Hopefully the dippers tuning frequency error is in the first case mentioned, such that the correction can be made via the
:::adding of a trimmer capacitance.
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:::73's de Edd

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:::EICO 710. . . . . . GRID DIPPERATOR SCHEMATIC :
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Eico 710 Grid Dip Meter 
Bob Z 04/03/2009 11:56 
Edd 04/03/2009 16:45 
Bob Z - Back to Edd 04/03/2009 18:25 
Bob Z - Photo Added 04/03/2009 18:42 
Edd 04/04/2009 11:00 
Bob Z 04/04/2009 17:57 

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