[R-390] Why 6DC6?

Fri, 06 Sep 2002 16:46:35 -0700

Hi all,  I took a look at the Carr article and felt good about the Mackay
3010 B I've been restoring; I don't think it's reached the 390a sensitivity
yet (just got it working) but the front end design is predicated on the use
of attenuation and a high pass filter for hf work to reduce cross
modulation.  A bc band 0.6 to 1.6 Mhz high pass filter can be switched in
to suppress strong bc stations and it works well;  the attenuator
additionally tames overload.  This receiver uses a sharp cutoff 7788 rf
tube (gm = about  50,000 mmhos !!!) and has tremendous front end gain.
Mackay sold other front end filters to handle specific strong station
problems for this set.  Several years ago I made a bc band high pass filter
from the 1982 ARRL radio handbook,. 8-59 that uses toroids and I tried this
in substitution for the Mackay filter - works about the same as far as I
could tell.   It's a 50 ohm filter but could be changed to other impedances
by scaling the inductors and caps.    I suspect it would work ok with the
R-390a but haven't tried it.  Dan

[email protected] wrote:

> Try looking at this......
> It is one of Joe Carr's Tech Notes.
>
> NOTE 6
> Dealing With AM Broadcast Band Interference to Your Receiver
> 10 Pages
>
> While it's not tube data it does strike the subject of BCB
> Interference.....
>
> Noted author, Joseph J. Carr, has created a series of short articles on
> topics of interest to the shortwave listener.
>
> <http://www.dxing.com/tnotes/tnote06.pdf>
>
> RICH WA6KNW
>
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