[HBR] Dials (was 'HBR 16')

[Walt Hutchens]

Introductory cliche: The dial you want really depends on what you're
trying to do.

When building an HBR-series receiver, both the National ACN (and
relatives) and the Eddystone are 'authentic': Ted Cosby built with the
National dials but many other builders used the Eddystone.

Advantages of the National dials are mainly ease of layout and
construction. They're also fairly inexpensive when you can find them.
The standard ratio is around 5:1 or 6:1 which, if you're tuning a 500
kcs band in that 2-1/2 turns is MIGHTY fast for tuning SSB. They're
satisfactory, however, for a vintage radio night set that will be used
mainly to receive AM.

An upgrade is the use of a Millen dial having a two-speed drive,
typically 36:1 for most of a knob revolution, then 6:1 thereafter.
Quick QSY but you get a slow enough rate for tuning in SSB when you
arrive.  These are planetary ball-type drives.

Jackson Brothers makes (made?) both a single-speed version of the
drive assembly for this dial and a two-speed one. They were available
in the U.S. (UK company) not long ago, maybe still are. These drives
with a home made dial scale and frame are an excellent combination of
construction practicality and good performance.

Planetary ball-type drives (and dial assemblies) are available on many
inexpensive junker sets but they are frequently worn to the point
where backlash will be annoying. A good bet if going this route is an
FT-101 series junker since the (single speed) front end tuning control
drive got a lot less mileage than the main tuning knob on other sets.
Metric dimensions on this set, for example 6 mm shafts. The Sideband
Engineers SB-34 sets are pretty common as junkers and they have the
two-speed version of this drive, though it's often worn.

Worn planetary ball drives can sometimes be much improved by pinching
the fingers that hold them together VERY SLIGHTLY with a pair of slip
joint pliers.

Planetary ball drives can require significant torque.  It's best to
mount them so that is transmitted to the panel rather than to the
chassis or (worst of all) the capacitor frame, to avoid backlash
issues.

If your metalworking skills are new or rusty, I'd say pick one of the
choices above. There's nothing more frustrating than being unable to
get the parts in the right place without chewing up a lot of chassis
and/or panel. The two speed planetary ball drives really can't be beat
for performance AND (with proper pointer and frame) vintage appearance
on an HBR-type set.

Layout and construction is straightforward: Set the capacitor on a
hard flat surface, measure the height of the center of the shaft, then
mount the panel temporarily on the chassis and measure up the same
distance. Be sure the chassis is FLAT. Use a flex coupling between the
dial and the cap but get perfect alignment so the coupling has no
visible work to do.

The tuning cap should have the lowest torque requirement possible,
consistent with no shaft side play. When the tuning cap is mounted
flat to a large chassis it's generally a good idea to stiffen the
chassis where the cap is mounted by epoxying a plate on the underside.

The Eddystone 898 is the top of the line for performance with strictly
vintage parts. 55:1 ratio, flywheel, sliderule type with logging
scale, can be lighted, very smooth. The 898 is, however, a four-star
B***H to lay out properly and install. There are basically three ways
to go about it: 1. With the cap shaft far enough above the chassis so
the flywheel doesn't hit -- easiest but a VERY high tuning knob. 2.
With clearance cutout in the chassis for the flywheel -- better knob
height but more work. And, 3. With the chassis spaced back from the
panel enough to clear the dial mechanism.

These are hard, harder, and a real mess, respectively.

Eddystone HBRs are laid out somewhat differently than the original
ones but that has all been worked out and the info is in the list
archives and/or on the CD.

Another possible avenue is old junker broadcast radios, particularly
the better models that had slide rule dials. While not a match for the
Eddystone, these can be quite good and they're both cheap and not too
hard to find.

The command set dials can't be beat for quality -- scissors-type
gears, and so on.  They were designed for a single scale (single band)
so they're not a great fit to an HBR project, but it can be done.
They're much better for a set where the main tuning is a tunable 1st
IF so only one calibration scale is required.

The big problem with multiple dial scales is that the knob shaft is
off to the lower right but close to the dial hub so you have a lot
less room for scales than you'd have with a central knob or one set
further off.

The command dial drives are integrated with a three-gang tuning cap
(receivers) or single gang cap (transmitters). You can, however,
remove the 'works' of the cap and install your own in that space. With
the dial on the front panel the capacitor shaft is PARALLEL to the
panel so the usual HBR layout requires considerable rework.

I made a dial for a miniature set from the drive for a command set
control box. This gives you a gear reduction drive with a
make-it-yourself pointer and an output shaft that's perpendicular to
the panel. There's metalwork but it can be done with hand tools and a
drill press. Quality isn't quite the equal of the command set itself
(gears are smaller) but it was entirely satisfactory.

With completely home brewed dials, the sky is the limit but the
metalwork can be a challenge. Browsing old radio construction magazines is
probably a good way to get ideas.

Walt
KJ4KV