[ARC5] Solid State Conversion of a BC-779

[Richard Knoppow]

    I downloaded it. I have a vague memory of knowing this 
article existed but maybe it was another.
    My first real receiver was a BC-779A. I still have it. It had 
been modified when I bought it, a well known mod from CQ magazine 
that replaced the pentode tubes with dual triodes. It worked but 
was not very satisfactory. I restored the original circuit and 
then made adaptors so that I could use miniature tubes. I left 
the 6J7 oscillator but modified the circuit to an electron 
coupled circuit I copied from a General Radio frequency meter. It 
was extremely stable but had low output. I tried various tubes 
for the RF and mixer stages eventually winding up with the 
conventional 6BA6 and 6BE6 which had the best AVC and overload 
characterists. I finally restored the circuits to original and 
found the old tubes loaded the RF circuits less resulting in 
better image rejection. The one mod I found worthwhile was 
installing a VR-150 to regulate the oscillator plate. The BC-779 
is an excellent receiver but does benefit from some help. I have 
this rig and must dig it out and replace all the caps, etc. The 
idea of converting one to solid state sort of boggles me. I will 
read the article and see if the designer was aware of the loading 
effects, etc.
     IMO the Super-Pro series was about the best of the late 
1930s to 1940s receivers with the exception of the RCA AR-88. 
However, the AR-88 was never sold commercially so really  isn't 
in the running. While the Super-Pro was the most expensive 
receiver sold for ham use my estimate is that the AR-88 would 
have been about twice the price.
    It is interesting to me that Hammarlund never used voltage 
regulation in the Super-Pro, even to the last of the series. They 
certainly knew of its advantages from the HQ-120-X and later 
similar receivers and also knew about temperature compensation 
from the same receiver but never used it in the Super Pro until 
the last of the SP-400 series. The Super Pro takes about 48 hours 
to stabilize but once there it doesn't move. The VR tube keeps 
the LO from pulling because of the effects of AVC on the plate 
voltage.

On 11/4/2020 12:28 PM, Robert Eleazer wrote:
> I was searching online for some info on the Motorola MFC9020 IC 
> after finding one in my junkbox, and look what I found:
> https://archive.org/details/solidstateconver00steupdf 
> <https://archive.org/details/solidstateconver00steupdf>
> Wayne
> WB5WSV
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL