More about the 1 Month HBR (Was 'Re: [HBR] Another Project -- 1MHBT')

[waltah at earthlink.net]

Dan wrote:
> Would you happen to have a schematic of this receiver available? I
>  have most of the parts to do something similar.  Could send you 
> SASE plus  cost of copying.  Am looking forward to seeing the pictures.

No schematic now; I'm waiting until the schematic is finalized to 
draw it.   I have promised Kees I'll do one.   

It's close, but details, details.  

Hardly anyone would want to duplicate this.  It's very cute (my 
opinion!) but the mechanical problems of plugging in the coils 
through the panel -- the main cuteness -- are considerable.  It 
requires mounting the coil plugs from the command receiver on a 
very stiff bracket which must be near-perfectly aligned with the hole 
in the front panel.  It's the dickens to lay out (where exactly *is* the 
top of the coil set relative to the plug on the bottom?  How do you 
even measure?) and not easy to cut -- a big rectangular hole with 
visible edges.  

Coil sets must be modified mechanically by drilling out the 
bushings in the ears and bending them out exactly right so they fit 
over the mounting screws.  The center coil can rivet must be drilled 
out and a screw used to mount the knob.  Three coils per band 
must be wound by cut-and-try; I can give turns counts and cap 
values that will make it easier but you've still got to adjust turns 
spacings and/or slugs to get good tracking -- there is no room for 
trimmers in those cans.  Got a big collection of small parts?  Very 
little room for the fixed caps that go in those cans, either.  I wound 
up with some of the osc. caps being silver mica rather than NP0 
ceramics because I didn't have the right item.  'Course knowing the 
values, one could mail order a lot of what's needed.  

Lots of trial-and-error and the coils are held in their respective cans 
with four 2-56 screws each.  

You do get better stability than for the usual top-of-the-set plug-in 
coil designs because the coil sets contain most of their respective 
tuned circuits, they're in cans so the temps are fairly uniform, and  
they're under the chassis and cooled by air flow inward around the 
coil set, and upward from the drawer beneath.  The osc coil temp 
rise is only 10-15 degrees which is a fraction of what you get with 
on-top coils.  

It helps that the coils are stowed in the drawer under the set so 
they're a bit above room temp already.  

Also it is easier/quicker to change on coil set through the front than 
three individual coils through the cabinet top.   

This is a home brew receiver for the ham whose other hobby is 
building big model ships in small bottles, just to prove that he can 
do it.  You'd get a set with somewhat more warm-up drift (few kcs 
vs. ~1 kc) but otherwise equal performance for half the work by 
building one of the last HBR designs like the HBR 13, possibly 
substituting better tubes -- 6EH7's and 6ES8's.  

Pics in a couple of days.  

Walt Hutchens
KJ4KV