[Drake] Carrier point adj. for TR4

[Garey Barrell]

Guillermo -

The adjustment procedure described in the manual works perfectly well, 
IF the two filters still meet specifications.  This method simply 
centers the carrier oscillator in the "trough" between the two filters.  
Some of the early filters, in particular the single can types used in 
the TR-3 and early TR-4, have had crystal or other failures over the 
years and no longer have a "rectangular" passband shape.  There is no 
carrier adjustment procedure that will compensate for this, and 
replacement of the filters is the only option.

A couple of things to check..   First, ensure that the Carrier 
oscillator is slightly below 9.000 MHz.  On some units it is possible to 
get the oscillator "outside" the filters on one side.  Second, you can 
get an idea of which filter is the problem by tuning slowly through the 
calibrator signal and watching the S-Meter.  The meter should rise very 
rapidly as you tune toward the cal signal, then "flatten out" for a 
little over 2.5 kHz, and then drop rapidly.  Do this on both USB and LSB 
filters.  You may find that one filter has a large dip in the middle or 
"droops" on one side, giving a slower rise or fall on the edge.  I've 
seen both.

The "dual" filters (two separate cans), whether painted gray, blue or 
unpainted "silver" are all the same electrically and are 
interchangeable.  Almost all of the failed filters of this type that I 
have seen are the gray painted ones, but I don't know if this is because 
they are just the oldest ones, or if there is a higher failure rate.  
They usually fail in a way that they are no longer rectangular, although 
I have seen one that just "moved" out of range while remaining 
rectangular......

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>



James C. Garland wrote:
> Hello Guillermo,
>
> I'm afraid I don't understand the question. I've never used "two 
> tones" to adust carrier oscillators, and I'm not sure how they would 
> be useful unless they were spaced exactly at the filter bandwidth.
>
>  Normallly, one just tweaks the oscillator frequency to put the 
> carrier on the appropriate edge of the filter bandpass, typically at 
> the 3 or 6 db point. The easiest way to ballpark the correct setting 
> is by talking into the microphone and listening to yourself on another 
> receiver.   Most transceivers also have a separate oscillator offset 
> adjustment so the dial setting doesn't change when switching beteen 
> USB and LSB.
> 73,
>
> Jim W8ZR
>
>
>
> At 06:30 AM 5/24/2007, you wrote:
>>         Has anybody tried susccesfully a two tone method for 
>> adjusting its 9 MHz carrier oscillator?. If so, which frequencies are 
>> used?. This rig has (I figure) both filters so aged that it's 
>> impossible to achieve good tx tones with a single carrier oscillator, 
>> at either Lsb AND Usb.
>>
>> TIA
>> Guillermo - LU8EYW.
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>
> *************************
> Jim Garland
> Santa Fe, NM
> www.w8zr.net
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