[HBR] RFamp circuit of HBR-11+

[amargosaent at iscweb.com]

Hopperdhh at aol.com wrote:
> Well it looks like I should have waited to ask the group this question.  I 
> carefully read the HBR-11 article, and it is no mistake.  Ted states that the 
> cathode resistor is not bypassed.  It always seemed to me like this could be a 
> source of feedback.  I know it is basically degenerative feedback, but at some 
> high frequency degenerative feedback can become regenerative.  Interesting 
> that the HBR-11 thru HBR-13C has been plagued by vhf and uhf parasitics!
>
> Dan K9WEK
>
>   
I will put in my two cents hoping to clarify the "why did Ted do it" 
question.   That two cent opinion is based on working closely with both 
Ted and Alex Stewart between 1965 and 1968,  including several visits to 
Ted's home near San Bernadino CA (I lived about 85 miles further west).  
All of this was in aid of my building the HBR-XX (so as not to confuse 
it with Ted's un-published HBR-20) that included the T-notch IF filter 
described in my 1969 QST article, the last of the HBR series.  In the 
process of visits, telephone calls and letters I learned a bit about 
Ted's career which speaks to why he did things a certain way (and often 
got a bit tart when  you challenged him about his reasons).

Ted was not designing the published HBR designs for himself (although he 
used lots of his own personal circuitry in the published designs), nor 
was he designing for a radio manufacturer  with trained staff, technical 
supervision and quality control to ensure the finished product pretty 
closely represented the design intent.  He was extremely sensitive 
(possibly overly so) to the fact that the builders of his designs were 
largely average hams, with a wide variety of receiver construction 
experience and vastly different levels of  general 
"how-to-build-it-right" knowledge.  I know for a fact he was overwhelmed 
with the popularity of his early  HBR articles in QST.  As Ted evolved 
the early designs into their more sophisticated forms, he struggled with 
just how much "tricky  stuff" he could publish before "Tom, Dick and 
Harry" (referred to in his letters as TDH) got themselves into trouble.  
For that reason Ted tried very hard to keep things  simple.  He did 
mention to me on one occasion that he felt the RF stage was important to 
the overall HBR receiver performance in the general ham environment, in 
part to provide some buffering and matching capability into the 
antenna.  Trans-match boxes did not exist in that era, and it was not 
uncommon to find hams using separate antennas for transmit and receive.

Ted also designed the entire HBR front end to regenerate creating a 
higher effective coil  Q and better mask the first detector noise.  That 
approach is referenced in the 1958 ARRL Handbook page 111.  The Handbook 
reference ends with the interesting sentence "This is a tricky process 
and another reason why regeneration is not widely used".  I found out 
just how "tricky" the regeneration process could be, and ultimately had 
to get assistance from Ted to resolve the problem.  It takes very little 
to upset the regeneration; both Alex Stewart and myself found that 
regeneration in the center-mounted Eddystone 898 receivers was somewhat 
less than in the end-mounted Eddystone 898 dial placement receivers.  We 
both independently concluded that the difference were caused by physical 
proximities to shields, cabinet sides, sub-assemblies and the like.  I 
strongly suspect the un-bypassed amplifier cathode resulted in part from 
Ted's tinkering with the regeneration issue.

Ted was a highly intuitive designer, the best I ever worked with.  He 
also had about 40 years of experience in building receivers for 
himself.  When I questioned him about his "receiver mania" he smiled and 
said he never found a commercial receiver which completely satisfied him 
in its performance, they were all just "too damn expensive", and he 
could do better in both categories with his home-brew contraptions!!  
With that amount of experience behind him, he had probably already made 
about 99 % of all possible mistakes and his work was near flawless.  He 
thought long and hard about publishing improvements to existing designs 
or new designs because of his concern that others without his experience 
and talent could enjoy a success.  As a case in point, he long delayed 
revealing his Hartley oscillator HBR modification until several of his 
cronies successfully built them and gave him a positive response to 
performance improvement and general lack of problems in design execution.  

I learned in working with Ted's design details it made sense to first 
built it the way he said, get it peaked up and understand its 
capabilities, and only then to begin my own tinkering.  I think that is 
still a good path to follow.

Hope my antique comments from experiences nearly half a century ago help 
others in understanding why Ted probably did some things that today may 
look a bit strange (and sometimes rather weird).

By the way, I agree with all the technical responses garnered by this 
thread.

73 de Jay W6HHT