[HBR] Another Receiver Project -- HBR-4, Part 20

[waltah at earthlink.net]

Kees:
> After reading all the informative posts and comments from others in the
> group, I certainly would like to see a complete schematic when you get
> done, Walt. 

Fair enough -- and it's a promise.  

> Maybe an article in Electric Radio would be appropriate ...

I agree, and that article has been in progress since the series of 
posts began.   It's a very different piece of writing since it needs to 
present a complete picture of the finished project with only the 
most interesting of the digressions detailed in 20 parts (and 
counting) on the list.   Rather a moving target, even though I don't 
try to keep it up-to-the-moment.  I'm about to go back to it and add 
the discovery that we've all been hooking up our beam tube mixers 
backwards.

I found two more beam tube receiver mixers in the RSGB handbook 
this afternoon -- they're backwards too.   Of course you can argue 
that 'backwards' is relative -- that even if hooked up with G1 as the 
signal input you get a high gain pentode mixer of pretty decent 
performance.   But I'm unable to find *any* general advantage to 
hooking up that way.   

> ... since I have not seen any more follow-on articles on the
> HBR-2000. 

HBR-2K remains an unfinished project.   I need to redo the RF 
stage for higher gain but unfortunately it already has RF 
regeneration so I've got to improve the shielding.   You should only 
see what that entails; it may be possible or it may not.  

In doing that design I completely forgot that the output of the first 
mixer contains a great deal of signal-frequency junk and must 
therefore be carefully isolated from the antenna circuits and RF 
stage.   

I learned a lot about front end layout from that effort and the HBR-4 
project has benefited: It has about twice the real estate for that 
section as compared to the 2K.

I don't think that one will ever get the level of documentation that 
the HBR-4 project should.   It's interesting mainly as an effort to 
translate the FT-101 receiver to vacuum tubes with the minimum of 
changes, for example it uses the same double-conversion scheme. 
I think it could be an excellent performer by the standards of the 
day but it's not there yet.   

And frankly, if I were looking for a project of this complexity I'd far 
rather tackle the HBR-4.   It's capable of a lot more (say an IFDR 
around 100 db instead of maybe 80) and I don't think it would take 
a nickle's worth of extra work, once the glitches are out of the 
design.   

As always, thanks for the encouragement.

Walt 
KJ4KV