[HBR] Re: HBR2K Explanatory Footnote

[hbr@mailman.qth.net]

For those who got in late on the story or perhaps don't remember 
every single list posting for at least two years, here's more on the 
idea behind the HBR-2K project.

I had been thinking of trying a ham-bands-only receiver but inlooking 
over the HBR designs, it seemed to me that while excellent for the 
time, they are today actually more difficult than necessary, for less 
performance.   I'm still watching for one of the Crosby HBR-xx series 
and will grab and restore it when I can, but for now I wanted to build 
something else.  

I first thought of building from scratch in the usual way, on a good-
size chassis.  That would keep a good'ol '50s look and approach.   
However, on studying my FT-101 parts radio, I noticed that its 
chassis is put together with screws, almost as if it were designed to 
be assembled from a kit.  Any sort of chassis mod could be made, 
just by making a new part and screwing it on -- including completely 
replacing the top plate.   

There are many advantages to this approach:  Front and rear panels 
already have holes for all the controls so problems of mechanical 
alignment of the VFO, bandswitch, and PRESELECTOR tuning 
mechanism are simplified or eliminated.   The FT-101 front panel is a 
sandwich with a steel subpanel that mounts the parts and an 
aluminum face.   I could do all the development and testing with just 
the subpanel, then make a new face when everything was working.   
And -- big plus -- the FT-101 cabinet (which has a removable top) can 
be used.   

Using the basic FT-101 structure means that many parts will fit 
directly.   Of course if the thing works and someone else wants to 
build it, it's much easier to duplicate a new top plate for the chassis 
and face for the panel than to do the whole business from scratch.   
The FT-101 has ample space for any likely receiver design.   It's steel 
framed -- no more power transformers sinking into the chassis if it's 
set down just a bit too hard.  And not a negligible consideration -- the 
typical 'really dead' FT-101 will set you back about $100 which is 
cheap, cheap,  for all the parts it provides.   At a guess, another 
$200 ought to provide all the rest and the total will be much less if 
one has a well-stocked junkbox.  

Ted Crosby's HBR-series is like almost every U.S.-made ham set of 
the 50's-60's in being basically a 1940's design updated to use early 
postwar miniature tubes.   Mr. Crosby's use of plug in coils simplified 
the construction of a receiver with performance rivaling the better 
commercial sets of the time but those commercial sets were way 
below what the state of the art would then have allowed.   

HBR-2K is an attempt at a home brew receiver using the best of what 
was available as the vacuum tube era ended, both in tubes and in 
circuitry.   In concept it ought to be better than any vintage set most 
of us have ever used and way better than anything but the better 
recent transistor sets ... but we'll see how it turns out.

I'm following the FT-101 conversion scheme, which for 80 meters is:

1st Oscillator: 9520 kcs (xtal)
1st (bandpass) IF 6020-5520 kcs
VFO tunes 9200-8700 kcs
2nd (fixed) IF 3180 kcs center freq.

With the one change that the 1st IF will be tunable over that range, 
rather than bandpass.   Successively higher bands use higher 1st 
oscillator frequencies so everything is converted to 6020-5520.   I am 
'getting religion' listening to World Harvest Radio at 5745 kcs and a 
Catholic station at 5825 kcs, while checking out everything from the 
2nd mixer on.

Circuit:

RF -- 6ES8 cathode coupled.  Will have AGC on both sections.

1st oscillator -- 12AT7, Pierce circuit using the tiny overtone 
crystals from the FT-101.

1st mixer -- 6ES8 Pullen circuit -- a cathode coupled design 
with excellent crossmod characteristics.

2nd oscillator -- Vackar circuit, 6DZ4 triode -- one of the last 
miniature tubes designed for UHF TV tuner oscillator service.  A 
stable oscillator at 9 Mcs is not as hard as one for *900* Mcs.

2nd mixer -- same as 1st.

Cathode follower (driver for crystal filters) -- triode section of 6KE8

Crystal calibrator -- pentode section of 6KE8
(circuit to be stolen from the FR-100B -- surely not a popular theft source, 
these days ...)

Filters -- the three regular FT-101 filters for SSB, AM, CW.  Will be 
diode switched as in FT-101

1st and 2nd IFs -- 6EH7s

Carrier oscillator -- 1/2 12AU7, Pierce circuit, crystals are hot 
switched.

Detector -- 1/2 12AX7, plate detector; for SSB the carrier is injected 
on the cathode.   

AGC -- 1/2 12AX7, plate detector.   Cathode returns to -140V, plate 
is 0 -> negative to suppy AGC.   

The detector, AGC, and RF gain control circuit is stolen nearly intact 
from the Tempo One, AKA FT-200.   

1st audio/paraphase amp -- 12AX7

Audio output -- 2x 6AQ5 in p-p

Audio is conventional; feedback is used from the speaker winding to 
the cathode of the 1st audio stage.

Power supply -- a 35 VA 120-120 isolation transformer 
feeding two half wave rectifiers supplying + and - 140 volts or so.  No 
regulation.   Filaments are a Radio Shack 12V/3A transformer.   
Another Radio Shack transformer is used as a filter choke.

Construction is basically "Obtain an FT-101 and strip to a bare 
chassis."   Then replace the top plate of the chassis with 0.050 AL, 
drilled and punched for the hollow state design.   I'm recycling the 
front end coils and tuning mechanism, bandswitch, all crystals, the 
VFO box, capacitor, and dial assembly, and many, many small parts.

Walt Hutchens
KJ4KV