[HBR] HB rcvr

[keith ford]

All these tubes are metal and came from old trashed
out BCB rcvrs.  I do have some glass equivalents/
versions.  I have the IFT's from all the rcvrs.  

I've decided to build in modules to ease in changing
circuits and trying different circuits.  At least that
way i can check each module as i complete it ( I hope
). 

I have not decided on which detector to use, the HB's
show at least 4 different ones.  With the modular
build i can try each one and decide which i like best.
 

I'm trying to locate some old QST articles on crystal
filters.  I've a large lot of 241's that seem as
though they would make a good filter.

I'll look for the 6SG&7's and in the meanwhile i'll
use the 6SK7's.

Thanks keith.

--- "Walter A. Hutchens" <waltah at earthlink.net> wrote:

> Keith asks:
> > I would like a monoband cw rcvr for 80 meters.  It
> was suggested that I
> > post here, for comments, etc.  I want to use all
> metal tubes, mainly
> > because thats what i have the most of along with
> octal sockets.   Heres my
> > line up,
> > 
> > 1) 6SH7 RF amp   2) 6K8 or 6SA7/6C5 mixer, 3) 6SK7
> IF amp.  4) 6AC7
> > detector 5) 6J5 bfo  6)  6SC7 Audio amp.
> 
> Just a few comments:
> 
> 1.  I'd be inclined to use a 6SG7 rather than a 6SH7
> for the RF stage.   
> Semi-remote cutoff instead of sharp cutoff, with
> similar gain.  
> 
> You'll probably provide RF and/or IF gain controls. 
>  If you use the same 
> type tube in both places (two 6SK7's or two 6SG7's)
> you have the option of 
> putting a single pot in the common cathode return
> line while if the tubes 
> have different cutoff voltages (those three tubes
> do) you shouldn't do that 
> as one will cut off ahead of the other, possibly
> causing you a distortion 
> problem.   
> 
> Frankly, I think I'd try a 6SK7s in both sockets as
> they will handle larger 
> signals.   If you really need more gain, 6SG7s are a
> direct substitution.
> 
> 2.  HI Q ANTENNA AND RF COILS!   Don't skimp here --
> unless you're 
> going to cheat and go with toroids, use the biggest
> forms and the heaviest 
> wire you can.   That will give you higher gain, so
> you can loosen the coupling 
> to the antenna meaning better RF selectivity and
> less trouble with mixer 
> overloading.   You have to be careful about coupling
> between the two coils 
> causing instability of the RF amp.
> 
> 3.  As I remember, the 6K8 is a memorably noisy
> mixer.   (Mid 1930's tube, I 
> think ...)   I'd go with a 6SA7/6C5 or even a 6SB7
> -- about twice the 
> conversion transconductance as I recall, and even
> better compared to the 
> 6K8.
> 
> Mixer noise isn't generally an issue on 80 meters,
> but low gain can be -- at 
> the least, by forcing you to use a better antenna or
> tighter coupling.    With 
> just one IF stage I don't think you have enough gain
> for AGC -- but that's 
> probably the way you planned things. 
> 
> What kind of detector circuit are you using?  Will
> you be providing 
> selectivity beyond the 12 kcs BW one would expect
> with a couple of 455 
> kcs IFTs?   This would be an ideal design to use
> some audio selectivity.
> 
> Definitely a classic 1946 design!   
> 
> Walt Hutchens
> KJ4KV
> 
> 
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