[HBR] So i'm gonna build an HBR-XX

Thu Feb 19 02:56:42 EST 2009

Hi Marvin,

    I used to do design work for Eddystone - you do NOT need to have 
Anti-backlash gears, or even spend very much! The problem with string drives 
is getting the tension right in the cord (and maybe finding proper dial 
cord).

    The answer? Take a ball race (important) front panel mounting shaft 
(best are those by Jackson). I expect you will use a 1/4 inch one. You want 
a long one so you can fit a flywheel on the rear of the shaft and a heavy 
control knob on the front.
    The next "trick" is to only use two BRASS pulleys with steel bearings to 
guide the string across the top of the visible dial itself. You need ONLY 
these two pulleys for the whole mechanism or maybe just one other if you 
need the sting to miss other components. Fewer is better. You can take the 
string across the bottom of the dial but it is than more difficult to get a 
smooth feel because the pointer tends to drag. You can reduce this with some 
PTFE sleeving at the very tip of the pointer.

    The next trick is to find a LARGE diameter pulley to fit on the shaft of 
the capacitor. You could say the larger the better. just under half the 
circumference is going to be the visible dial length.

    Now, the capacitor is mounted on your chassis. It goes in with the shaft 
VERTICAL and in such a position that the string track around the rim of the 
large pulley is asymptotic to the line of string across the top of the dial. 
The pulley should be at the height of the control shaft. This means the 
position of the capacitor is fully defined in 2 dimensions, you can choose 
where you want it "left to right" so long as it is within the width of the 
proposed dial "window".

    The next drill a hole in the flat face of the large pulley so you can 
fit a long solder tag or similar. The string tension spring goes through the 
hole at the tip. You want a short stiff spring.

    String the dial, two full turns around the front panel shaft, one turn 
on the large pulley.

    Fit the flywheel and a heavy, well balanced, pleasant feeling, knob.

    The final trick? Finely adjust the string tension using the "solder tag" 
mounted on the large pulley.

    You will easily be able to make a dial whereby you have the feeling if a 
fly leaned on the control knob it the dial would move imperceptibly slowly 
and if you give a single twist of the wrist the pointer will travel gently 
all the way across the dial (this, not the part with the fly, was the test 
for Eddystone dials).

    Backlash? None if you get the tension right AND use PROPER dial string.

    Disadvantages? Because the large diameter pulley lands up horizontally , 
it can take up a lot of otherwise useable chassis area.

    Advantages? Deliciously homebrew and very inexpensive - you can adjust 
the "gear ratio" easily by turning down the groove in the panel shaft, just 
do not go too far. Which brings me to a last, final, trick. Make sure the 
string groove in the shaft is absolutely in line with the plane of all the 
pulleys taking account that the string runs in the "groove" in the rim of 
the pulley.

    Sounds difficult, but try it! It takes me about 2 minutes to get the 
string tension right using the "adjuster" on the pulley.

        73, Ron G4IZS

----- Original Message ----- 
From: "Marvin Match" <match at ece.utah.edu>
To: <hbr at mailman.qth.net>
Sent: Wednesday, February 18, 2009 10:49 PM
Subject: Re: [HBR] So i'm gonna build an HBR-XX

> On 18 Feb 2009 at 12:00, xjakobx at gmail.com wrote:
>
>> Hello List!
>>
>> I'm starting to gather together parts for my HBR-styled construction
>> project. It's a long way from being started, but hey, i gotta get the 
>> parts
>> together sometime, right?
>
> ---snip---
>
> A dial mechanism will be difficult. I've been looking for some time,
> and I have a National or two, but I really want an Eddystone. At this
> point I don't expect to find one.
>
> So, I'll be making my own slide-rule mechanism. I'll share it all
> with the list, but I don't expect to make much progress for another
> month or so. I really wanted a gear-reduction dial made with anti-
> backlash gears, but the gears themselves are expensive, so I found a
> variable cap made by TRW with an integral 6:1 ball reduction built
> into the shaft and I'll put a 6:1 Jackson ball reduction drive in
> front of it. That'll get me 36:1 reduction. I'd prefer about twice
> that, or three times that with a two-speed reduction, but I won't
> live long enough to find the parts to build it that way.
>
> BTW, the National and Jackson reduction units are not all the same
> either. Line up 10 identical Nationals and each one will feel
> different. The Jacksons are more consistant and generally feel better
> than the Nationals, but the same holds true. The best that i've found
> are the ball reduction drives that you see on some military equipment
> that have threaded parts that you can take apart. Not sure who made
> them. Next is the Jackson like found in Heathkits, last is (most) of
> the Nationals, although like I said, once in a while you find a
> National that feels really good.
>
> Another thing that will be difficult is the power transformer. Fair
> Radio Sales has one that might work. It's their TR180 for $18 here:
>
> http://www.fairradio.com/catalog.php?mode=view&categoryid=1545
>
> You'll need to add another transformer for the tube heaters if you
> choose this one as 1 A. @ 6.3 V. is not enough.
>
> Coil forms are near impossible to find for reasonable money.
>
> **Note to list: Anybody have spare coil forms?
>
> I've been making my own out of 5-pin tube bases and 1 1/4 inch
> acrylic tubing with 1/8 inch wall thickness (I think that a 3-foot
> remnant piece was $12 from the plastics store). I tested all of my 5-
> pin tubes and any that didn't test into the "good" range on my
> Jackson tube tester were sacrificed for coil bases. I chuck the base
> in my lathe and cut them down to .6 inches in height. Then if it's a
> fat base I machine the inside to accept the 1 1/4 inch tubing. If
> it's a skinny base, I machine the 1 1/4 inch tubing to fit over it.
>
> **Note to list: Anybody have some 5-pin tube bases or
> weak/dead/shorted 5-pin tubes they would be willing to pass along to
> me? I still need about a dozen for the two projects I'm working on.
>
> Then, you'll need an enclosure to put it in. They too are hard to
> find. I found a B&K 1077B TV Analyst for only a few bux and after
> gutting it and making a new front panel I have nice enclosure with a
> hinged flip-top lid! In fact I bought two... one for my HBR and one
> for a matching transmitter. I think I paid $20 for the first one
> (locally) and $35 (total including shipping off e-bay) for the
> second. Watch e-bay, check around town. These were never all that
> useful, but they're entirely useless now, so a local repair shop
> might just give one to you if you make friends with them.
>
> There's one on e-bay now if you want to see what it looks like. It's
> auction number is 230325967. The enclosure is worth the $30 starting
> bid on this one, but maybe not after the $40 shipping is tacked on,
> at least not to me. There's also a 1076 on e-bay that could be
> another possibility for an enclosure. These come up for auction all
> the time, so don't be in a hurry. Sooner or later one will be listed
> on e-bay that's close enough for you to pick it up.
>
> A good variable cap is essential. Most anything out of a tube-type FM
> radio will work, but they're not all the same, and actually they're
> just a tad too small anyway, an extra pf or two at the top end or a
> pf or two less on the bottom would be better. I can't speak for the
> one you've found, it might be fine, but if you ever get the chance to
> get the one Ted specified... GET IT!
>
> I've thought about using one of the AM-FM caps like the one you've
> found, and using the two larger sections to cover 160 with no RF amp,
> but to do this easily you'd need 6-pin coils so that there's an extra
> pin for the 160 coils to catch those big tuning cap sections, and
> I've already invested a lot of time building 5-pin coils.
>
> WOW! Am I long-winded or what?
>
> Keep us posted, Jake.
>
> Marvin
> KA7TPH
>
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