[HBR] HR-67

[hbr@mailman.qth.net]

In a message dated 4/11/02 11:13:35 PM Eastern Daylight Time, 
vze2gmp4@verizon.net writes:

> OK! That explains why I can't find it. Don't have those handbooks.

>  > The HB-67 is an 80 meter receiver having a 455 kHz IF, a crystal 
> controlled
>  > converter for the 40,20,15, and 10 meter bands, and a solid state power
>  > supply all on one chassis. The coverter is switched out of the circuit on
>  > 80 meters. Selectivity is fixed at 2.1 kHz by the use of an SSB 
mechanical
>  > filter. Audio-derived AGC is provided, and the 80 meter section uses a
>  > single-ended 7360 mixer.
>  
>  From your description it does't sound like my cup of tea.

What sort of design do you favor? I'm partial to premixer designs, myself.

>  > There are other beam-deflection tubes that are more common and cheaper 
> than
>  > the 7360. The 6JH8 and 6ME8 are often-overlooked examples.
>  >
>  > The Pullen mixer design is credited with high performance yet is simple 
> and
>  > sure-fire. The recommended mod for the 75A-4 first mixer is a 6ES8 Pullen
>  > mixer over the 7360.
>  
>  That's basically the 6J6 dual triode mixer I mentioned.

OK. When I get building again, a Pullen mixer will be tried. 
>  >
>  > >  -No RF stage
>  >
>  > This can cause problems with IF feedthrough, images and spurs, but is a
>  > good idea if you can get adequate RF selectivity ahead of the first 
mixer.
>  > I have often thought that a double-tuned input circuit using really BIG
>  > Miniductor or other high Q coils might be the answer.
>  
>  A couple of tuned circuits is the answer.  Many people think they HAVE to 
>  have an RF tube in there.  Not so until one hits 15 Mhz or so.  I have 3 
>  receivers that don't have an RF stage.  Don't miss it on 40 mtrs.  
Choosing 
>  an IF freq.  is important.  Running only one mixer oscillator makes things 
>  alot easier to clean up.

The need for an RF amp depends on a number of factors. Usually their function 
is 
to compensate for a noisy first mixer and to deal with the losses in the RF 
coils. Plus
contribute some gain to the set. 

With a good set of hi Q coils and a lownoise mixer those concerns are reduced 
or
eliminated and the RF stage becomes less important. A good beam-deflection or
Pullen mixer is actually quieter than many RF stages. 

But eliminating the RF stage and therefore the pre-IF gain means that more 
attention
must be paid to the noise figure of the IF amplifier, particularly the first 
IF stage. 
>  >
>  > >  -Modular construction
>  >
>  > A good idea but drastically increases construction time.
>  
>  Time I've got.  I'm really looking to make this receiver more flexible for 
>  future mods.  One receiver I have, I built with the front end modular.  I 
>  have 5 different modules built in 2.5 x 5.0 inch miniboxes.  The 
"standard" 
>  6xxx RF with a 6BE6 mixer is really the worst setup I have.  Cheap and it 
>  somewhat worked, for the manufactorers.  The dual triode is about the best 
>  (no RF stage).  The 7360 module I have is setup as a real balanced mixer 
and 
>  is a bear to keep balanced.  Using this tube single ended which most 
>  designers do seems to be defeating the purpose of using it. 
>  
Agreed. 

I have found the 6BA7 to be a worthwhile improvement over the 6BE6, if you
have to use a pentagrid mixer. Almost any receiver that uses a 6BE6 can be 
easily
converted to the 6BA7. Toughest part is changing the socket to 9 pin. 6BA7 has
lower noise, more gain, and needs less LO drive.

>  Thanks for the input.  CU on the list.

73 de Jim, N2EY