[HBR] HBR -- Part 15

[Walt Hutchens]

The 117Z6 dual diode has been replaced with a 117N7 rectifier-2nd
audio stage.  I triode connected the pentode, since the 1st audio is a
pentode.  The 6BH6 RF stage has been replaced with a 19JN8
pentode-triode, with the triode reserved for the 3.5 Mcs marker
oscillator.  And the 12AU7 socket is gone.

There are pictures of the set at:

http://picasaweb.google.com/timbreblue/Walts2008project#

If there are only 6 pictures, check back at a later time as I'm
waiting on the very busy webmistress to upload three new (current)
pix.

About the next step is the BFO and revisions to the plate detector
stage so it'll copy SSB and CW. Then the marker oscillator -- at last,
an EASY job!

AND ... with the latest shuffle of stages, my head has cleared enough
to see how to get a reasonable layout -- one with short leads, etc. --
on that chassis.  Additional advantage: I can get there without having
to rebuild from scratch.

At present, the local oscillator and 1st IFT are in the shield box
next to the antenna coil. The oscillator tube is about 4" from the
coil, and each is 2-3 inches from that section of the tuning cap and
the mixer. There are other, less easily described problems causing
various minor issues including extra shielding requirements.

I will shift the IF section to the left (seen from the front) by one
stage, moving the detector/1st audio into the vacated 12AU7 socket
hole, adding a new hole for the 3rd IFT beyond the current left end of
the IF chain, making the current detector socket into the 2nd IF, the
current 2nd IF stage into the 1st, and the current 2nd IFT will become
the 1st. The current 1st IF stage will become the oscillator stage.

The corresponding triode stages will have to move at the same time;
they're carefully placed to share nicely with their respective
pentodes and there are almost no options.

This rearrangement shortens leads -- often by half or more -- in four
different places, as well as giving a more logical layout and signal
flow.

I may either leave the oscillator coil where it is, or move it into
the shield box using the space vacated by the oscillator tube and 1st
IFT. (There are advantages both ways.) If that's done it'll need a
shield to separate it from the antenna coil.

Probably will leave it where it is, because it needs as much clear
space as possible to avoid instability caused by proximity of shields
and other stuff.

That'll be somewhere between a few days and a few weeks of work, even
moving those Western Electric sockets (with built-on terminal strips)
as assemblies ... but I have time to think about it while the BFO and
detector get working.

Getting close to the end of the building ... coils for the other bands
by summer?  A cabinet in the fall?

I'm going to see if I can order custom crystals in HC-49 (is that the
tiny wire lead one?) holder.  Does anyone have a favorite company that
does this work?  Ugh ... hope I can get 1.7 Mcs crystals in that size.

Walt
KJ4KV