[R-390] A 6kc. mechanical filter for a R-390a?

[Al S.]

Thanks to Charles we have the information on suitable matching of the
filters I already have here. Gotta wind some toroids etc. This filter will
replace the 16kc. filter.

Al
On Jun 16, 2017 12:01 PM, "Al S." <racalra17 at gmail.com> wrote:

> Hi Charles
>
> Thanks for passing along all the information on the 6790 mechanical
> filters.
>
> I purchased these from Gary Harmon? if I recall correctly. He refurbed
> those receivers in the past and sold parts.
>
> He did provide a table with the 7883-4 or 526 9957 040. 6kc filter,
> showing the resonating caps for all six mechanical filters. 7883-1 to
> 7883-6.
> The table indicates the 750 pf caps used for the 6kc filter.
>
> Al
> On Jun 16, 2017 11:09 AM, "Charles Steinmetz" <csteinmetz at yandex.com>
> wrote:
>
>> Al wrote:
>>
>> I'll have to have a look at how this 6kc filter is terminated etc in the
>>> Racal 6790 receiver. Its not one of the physically tiny torsional
>>> filters. The only info that I have with the filter is that it needs a
>>> 750 pf. cap for resonating on the input and output of the filter in the
>>> circuit.
>>>
>>
>> The 6790 terminates the filter inputs with 4.7k ohms and the filter
>> outputs with 5k ohms (2x 10k in parallel).  The different filters use
>> different resonating capacitors, from 82pF to 750pF (see table attached
>> below).
>>
>> The manual does not provide sufficient information to say what the
>> correct resonating capacitors are for the 6kHz filter (at least, not in the
>> schematic and parts list -- I didn't read any of the text).  One of the
>> filters does use 750pF + 750pF, but I can't say which one from the
>> information at hand.  (Note that some of the filters use different value
>> capacitors on the input and output.)
>>
>> Best regards,
>>
>> Charles
>>
>>
>>
>> ______________________________________________________________
>> R-390 mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:R-390 at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>