[HBR] Re: HBR Digest, Vol 54, Issue 5

[Marvin Match]

On 13 Aug 2008 at 4:01, Peter Bertini wrote:

> Hi
> 
> I'm undertaking what will be an modified HBR-16 receiver project, and
> right now I am in the gathering parts stage and have probably 90
> percent of the materials needed--inlcuding the coveted Eddystone dial!

Lucky dog!

Finding the coil forms are what's giving me grief.

> One thing I'd like to try is using balanced mixers for the first and
> second mixer, and for the PD  using 6JH8 tubes.  I'm wondering how
> these tubes will perform on the upper bands, where Ted used the 2nd
> harmonic of the LO to drive the mixer? I have a feeling that these
> tubes aren't suited for this application, and that may limited my RX
> to 30 meters and below. I'm also wondering which injection scheme
> would work best with these tubes using 2nd harmonic LO injection--LO
> injection to the control grid, or balanced LO injection to the
> defector electrodes?

As Tim pointed out, forget about using harmonic injection, otherwise 
they'll work FB on the upper bands. 

I'm not sure that it's justified for the PD however, as the 6BN6 is 
quit good here.

It's interesting that you mentioned these tubes at this time. I 
happen to be working on a very similar reciever. I'm currently 
investigating the use of a long-tailed pair for the LO in order to 
get the 2 signals 180 degrees apart to drive the deflection plates. 
Current thoughts are to use a triple-triode compactron in this 
application. Another choice might be a more conventional LO followed 
by the long-tailed pair configured as a buffer stage to provide the 
drive needed. That's kind of my fall-back position. Now that 
vacations are over, I'll be breadboarding these circuits and report 
back here and on GlowBugs.

6AR8 is similar to the 6JH8. 6ME8 is another but it requires 3 times 
as much drive to the deflection plates.

These mixers are quiet, so you no longer need the RF stage. In my 
case, I want a very narrow bandwidth front end, so I'll add a couple 
more tuned circuits to the preselector, and use a 5687 in grounded-
grid as an RF stage just to make up the losses.

> I am also looking for a source for a 1685 kc crystal, since I wish to
> use some salvaged ARC-5 IF transformers for the 1600 and 85kc IF
> stages.

I have these IF trannies as well, and some of those specified in the 
earlier articles to choose from, but they're just so BIG. When you 
start laying out the chassis it is amazing to me how much larger it 
needs to be when using IF transformers of this size compared to the 
3/4 inch K-tran types. So, I'll keep looking for K-trans as I work 
through my bread-boarding experiments. 

I think I would move the 1st IF freq above the BC band, to about 1700 
Kc or so also, and put your crystal at 1615, if you can find one.

> Has anyone had sucess using the ARC-5 BC453 BFO coil in one of
> these receivers--I've seen them used in some of the photos on the web
> pages, but I haven't seen any written comments regarding the same.

I've heard tell that it's not a good choice. Not sure why that might 
be. This is another candidate to be bread-boarded, I think.
 
> I've noticed that the IF half-lattice crystal filter Xtals from a
> Heath HR-10 are just about ideal for conversion between a 1600kc first
> IF to 85kc. I'm also wondering if the HR-10 tuning cap wouldn't be a
> good candidate for the HBR receivers?

Possibly. As of late there has been a fellow selling 3-gang 25 pf 
variables with built-in 6:1 ball reduction drives on eBay. I think I 
bought 2 for $12 or some such. Last time I looked they were still 
there, but that was a couple weeks ago. Aparently the guy had a case 
of 'em.

Most any 3-gang variable from an FM broadcast reciever is similar, if 
just a bit too small, but none will feel quite like the ones Ted 
specified, and you'll have to fiddle the coils to match.
 
> Sorry for all the questions, but all input will be appreciated.

Not at all. 

Marvin
KA7TPH