Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- James -
You have two of the four differences. #3 is the addition of an RC network in the AM filter slot that essentially uses the roofing filter (six poles + two additional poles in the NB-7A Noise Blanker) as the IF filter. #4 is the plastic trim strip on the front panel that says R-7A. Unfortunately Drake was selling these "over the counter" at the end of the spare parts "fire sale" a few years ago.
The only difference between the 4 kHz and 6 kHz filter with the synchro-phase AM detector is the selectivity. The detector works fine with either one, so if you want a "recovered" signal bandwidth of ~ 300 - 4300 Hz use the 4 kHz. The 6 kHz will give approximately ~ 300 - 6300 Hz. So just like any other filter choice, you can give up "fidelity" for "selectivity".
So far as I know, there was only one version of the R-7 Operation manual which was "overprinted" with a brief list of the changes above, otherwise identical, and only one Service Manual. ALL R-7/As have the MC1496 product detector, which was the primary circuitry difference between the TR-7 and TR-7A, and covered in the Revised TR-7 Service manual dated October 1980.
73, Garey - K4OAH Atlanta Drake B & C-Line Service CDs <http://www.k4oah.com> N5ARW wrote:
N5ARW <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- I was very pleased to finally get a R7 this weekend, and I have a few questions for the group. 1) What are the differences between the R7 and the R7A. I know that the A included the noise blanker and the 500 cycle CW filter. This one has the NB and after a little surgery, it is now fully loaded with filters. Were there any circuit changes? What about the surge protection that was added to the antenna input on the TR7. Did the R7A have than change also? There is a nice discussion of the differences between the TR7 and TR7A on WB4HFN's web site. Is there a similar writeup about the R7? 2) The radio came with a 6KC AM filter installed. I read on JM Cherry's web site that the synchro-phase AM detector works best with the 4KC filter. Is it worth changing the filter? 3) I also have a 1979 version of the service manual. Were there different versions of the manual as there was for the TR7? Thanks & 73
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