[HBR] HB-67

[hbr@mailman.qth.net]

In a message dated 9/28/03 11:54:31 PM Eastern Daylight Time, 
waltah@earthlink.net writes:


> > Has anyone built the HB-67 from the ARRL 1967 handbook? If so what
> > did you think of the performance ...
> 
> Haven't built it, but have certainly stared hard at it a few times.


Me too - the '67 Handbook was the first modern Handbook I owned. 

> 
> The beam deflection mixer has four potential advantages:  (1) Very 
> high gain.   (2) Outstanding large signal handling ability.   (3) With 
> the input signal on the grid and a balanced VFO feeding the 
> deflection plates, isolation between the VFO and the signal is 
> outstanding, meaning no trouble with pulling of the VFO.   (4) With a 
> balanced mixer output circuit, you get outstanding rejection of 
> signals at the IF arriving from the antenna.   
> 
> In the HB-67 design, advantages (3) and (4) are not realized because 
> the VFO feed and mixer output are unbalanced.   (2) is realized in 
> the mixer tube itself, but it feeds a mechanical filter -- they're *not* 
> good large signal handling devices and neither an RF gain control or 
> AGC on a pre-filter stage is there to help matters.  


It would be interesting to know how good or bad the HB-67 really is.  
> 
> 
> The one remaining advantage is the high gain ... but on 75 meters 
> gain's not the problem -- the ability to handle large unwanted signals 
> without non-linearity (which leads to trashing nearby weaker sigs 
> you want to hear) is more important.   

There does need to be enough gain to make up for the losses in the input 
tuned circuit and mech filter, though. Also, having adequate gain means no RF 
stage is needed. Finally, the front end has to be gainy enough that the first rx 
stage and not the first if stage noise is the dominant factor.

> 
> To this situation is added a 6BA6 RF-6D10 mixer converter to cover 
> the bands above 75.   

I always wondered why they did that, instead of another 7360. The 6BA6/6D10 
converter did not save money, space or milliamps.

As a second mixer the 7360 has all the issues 
> 
> it had in the first mixer job, plus it's handling *even larger* signals 
> because of the preceeding gain.
> 
> In my opinion this design is noteworthy mainly as an attempt to 
> apply the 7360 to an amateur receiver.   It is not, however, a well 
> conceived application. I believe that the later W6TC HBR designs will 
> give better performance.   


All depends what you mean by "better". The HBR designs can be drifty because 
of the high frequency LO. The selectivity in a W6TC rx is so far from the 
antenna (3 stages until the first 100 kc. IF can, and it's not the entire 
knothole) that dynamic range has to be comrpomised compared to a single-conversion-one 
stage-before-the-filter design.
 
> 
> For a comparaison, take a look at the 'Junior Miser's Dream' receiver, 
> also in the '67 handbook.   A 7360 mixer is used without an RF stage 
> on all bands although a signal-frequency Q-multiplier provides some 
> gain when needed.   (The Q-multiplier makes pretty good sense -- if 
> you're listening to a strong signal the Q multiplier can be backed 
> down but for pulling out a weak one, higher gain for the desired signal 
> with better rejection of off-frequency sigs is the ideal combination.)   
> The crystal filter was used, first because a higher 1st IF is needed on 
> the higher bands (3300 kcs) but also it has better large signal 
> handling ability than a mechanical filter.  

Only two poles, though.

 Only one IF stage is used --
> 
> though a 6AU6 (sharp cutoff pentode) is a strikingly poor choice.   


Agreed.

> Overall, the design has only a reasonable amount of gain; it should 
> do much better than the HB-67 at handling conditions on the modern 
> ham bands.   
> 

Better yet, take a look at the original "Miser's Dream", circa 1965 in QST. 


> Operating the VFO directly on each band probably means the JMD is 
> less than SSB-stable on the highest bands, but the same was true of 
> most ham receivers of the time.   
> 
> If I were going to do something like this I'd build something like the 
> JMD but use the plug-in coil scheme of the HBR-series -- higher Q 
> that way, and easier construction.   Or if bandswitching is desired, 
> then use toroids in the front end.   Leave out the Q multiplier.  (Or 
> leave room to add it later if desired.)  
> 
> 

The Q multiplier was a "poor man's RF stage", used to improve image response. 
A single tuned circuit of ordinary Q doesn't have very good image rejection 
on the higher bands unless the IF is really high.


How about this:

1) Start off with a double-tuned input circuit using nice big high Q plug-in 
coils. Two windings on the same form, spaced for critical coupling. 

2) Balanced beam deflection mixer OR a low noise Pullen mixer.

3) Premixer-type LO chain using a unit VFO operating at a relatively low 
frequency, and plugin premixer assemblies for the other bands.

3) Selectable CW and SSB xtal filters right after the mixer.

4) One stage of 6EH7 IF

4A) Second set of filters if available.

5) Second mixer (Pullen?) so BFO is not on same freq as IF. AGC is IF derived 
from original IF freq. 

6) Good product detector, with xtal BFO in a separate shield box

7) Triode audio.

8) Separate power supply to keep heat down.





> 
> You can either use the crystal filter scheme of the JMD or go with 
> conventional IFTs and double conversion as in the HBR series.   Do 
> balance the mixer output, don't provide too much IF gain.
> 
> (I don't know why the JMD designer didn't balance the mixer output 
> since he already had an output coil in the circuit and just had to give 
> it a center tap.)

There's more to a balanced beam deflection mixer than just splitting the 
output coil. The SS-1R schematic gives me a headache.

> 
> Use a 6EH7 IF tube -- more gain than a 6AU6 and much better large 
> signal handling.   (The AGC voltage will need to be higher -- a higher 
> ratio for the transformer would do it or you could use a full wave 
> bridge to rectify the AGC.)  Build a push-pull VFO -- except for 
> needing a split stator tuning cap it's no harder than singled ended; a 
> given level of design care will give you better stability (because the 
> tube capacitance is effectively halved); and with attention to balance, 
> you'll greatly reduce oscillator pulling.   


Or better yet, use a phase splitter/isolator tube to get balanced drive 
without all the complexity

> 
> And use a later tube than the 7360.   The 6JH8 and 6ME8 (I think) 
> are both improved and certainly a bunch cheaper and easier to 
> locate.   The voltages and pinouts are different, but as far as I know, 
> they do the same job and do it better.
> 

I don't know if the later tubes are better, but they sure are cheaper! 

The 7360 was considered a trqansmitting tube by RCA, and the 6JH8/6ME8 were 
TV receiving tubes, meant to reduce parts counts and complexity in colorTV 
receivers.

See also the W1KLK receiver article ("An Experimental Receiver For 75 Meter 
DX Work") in QST around Feb 1971.

Except for a few designs like the DCS-500, I find the more complex Handbook 
tube receivers after about 1950 to be a bit lacking. Most don't have CW 
selectivity, even though it was essential for all but the most casual CW work. The 
tuning dials used were not the best, particularly given the availability of the 
Eddystone dials and surplus units like the ARC-5 transmitter caps. (I think 
there was a "no surplus" policy at Hq). And the Pullen mixer is absent, even 
though it appears in the RSGB handbook.

An improved "Miser's Dream" may be the ultimate answer.

73 de Jim, N2EY



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