[HBR] I'v finally started the HBR-16

[hbr@mailman.qth.net]

In a message dated 1/24/04 10:03:59 AM Eastern Standard Time, 
Bill@LizCurtisHiggs.com writes:


> Now that the holidays are behind us, I have finally got a start on the HBR. 
> Currently, all that is done is basic metalwork and planning, but I expect to 
> drill more holes over the weekend and maybe even mount the tuning mechanism 
> and some tube sockets.


Before you do, hear me out about the tuning cap.

> 
> 
> Plans are to follow the HBR-16 architecture, but with a couple of tube 
> changes. I'm going to try a 6eh7 as both RF amp and IF amps, a 6EJ7 as first 
> mixer, and the 6U8A circuit from the HBR-13 as second mixer. 

Be aware that the 6EH7 has a lot more gain than the original tubes, and may 
be a real bear to tame. Plan from the beginning to put a shield on the tube 
socket to separate grid from plate, etc. Bypasses everywhere, etc. I've used that 
bottle for years and it's not nearly as tame as a 6BA6 or 6BJ6!


Second IF is at 85kc (not Hertzes), using command set cans, possibly adding 
an 
> extra can for additional selectivity (thanks, Walt!). The 6JH8 product 
> detector from the "KCS Compactron" looks like it is worth trying (thanks for the 
> schematic, Pat!).

All good. In fact you might even consider double cans between each 85 kc. 
stage. 


> 
> Tuning will be with an old National 5:1 dial (yes, I know it's too slow, but 
> I'm adding a small "clarifier" control in parallel. 

In a receiver of such complexity, consider using something like a Command set 
capacitor. Built-in splitgear drive and dial, very smooth, very rugged. If 
you want a 3 gang, the one in a BC-455 is 62 pf per section. 

Also, rather than plug in coils, I'm going to try the "band imaging" concept, 

> covering both 80 and 40 with a single VFO range. If I want the higher 
> bands, I'll try an outboard converter . . .

Could also use a Command set tx cap for the VFO and a ganged 2 section for 
the input preselector.

And now for something completely different...

(Possible heresy beyond this point)

If the rx is only meant to cover 80 and 40, an RF stage isn't really needed. 
A good
mixer (6EJ7 is very quiet) and a double-tuned input circuit will do the job 
with a 1700 kc. IF. Of course you need a little more gain somewhere else, but 
with 6EH7s in the IF, getting enough gain isn't likely to be a problem. 

Good luck whatever you decide! Please keep the pictures coming.

73 de Jim, N2EY 


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