[HBR] HBR-?

[hbr@mailman.qth.net]

In a message dated 1/25/04 9:34:40 PM Eastern Standard Time, 
Bill@LizCurtisHiggs.com writes:


> I spent the afternoon mounting a BC-453 tuning cap onto the chassis (front 
> panel, actually), with much sweat making the holes line up. 

Aw, heck , I forgot to tell ya the trick...

Use a piece of thick paper as a template. Cut holes for the knob and dial 
shafts, rub pencil to find the mounting holes. Goof around with it and some thin 
card stock until all the holes are right. (Cardboard is cheaper and easier to 
mess with than metal). Then tape it to the panel, center punch, and drill. No 
sweat.

As I anticipate a 700Kc tuning range, I should be able to use one section of 
the 
> cap in a relatively high C circuit. 

Or two...

As I'm using a dual 150mmf (Millen?) in the preselector circuit to tune both 
80 and 
> 40, I'll not be using the other two sections. I realize a linear tuning 
> scale with this unit may be a pipe dream, but it gives me about a 30:1 ratio and 
> actually simplifies some of the mechanical work.

One linearization trick is to put a fixed cap in series with the variable. By 
careful choice of series C, parallel C, and L, you can get pretty close. 
While the solution can be found mathematically, cut-and-try may be quicker.

Some folks also prefer a bit of nonlinearity. For example, someone who is 
primarily a CW op migh like having the low end spread out really wide, yet retain 
coverage of the 'phone band.

Question: why a 700 kc. tuning range?  


> 
> Thanks, Jim, for the "heads up" on the 6EH7. What are your thoughts on 
> ditching the RF amp, using another 6JH8 (similar to the 7360) as a mixer, and 
> keeping 6EH7s as IFs?? 


NICE! But I don't know if you really need a tube as hot as the 6EH7 at 85 kc. 
Of course you can always run it at less than full gain and have lots of 
headroom.

Do you have 6JH8s, or have to buy them? If you have to spend $$, why not try 
a Pullen mixer first? Any of the common dual triodes is worth a shot at 80/40. 
6BZ7?

This would be similar to the Squires-Sanders circuit, although with a 
different 
> conversion architecture. Not too far off from the G3PDM receiver of late 
> '60s vintage. I'm trying to work with parts on hand, as I've set an upper limit 
> of $100 for the project.
> 
> If I stay with the HBR RF/Mixer, I'll do the product detector similar to the 
> mod shown in QST, but using the 6JH8 ($3) rather than the 7360 ($50). It has 
> a bit more gain, and I may be able to get away with skipping the audio 
> preamp.

I may just try that 6JH8 in the Type 7.


> 
> At any rate, I'm allowing for changes as I go. Even the best laid plans . . 
> .
> 
> 


One more idea....

Most of the bandimaging receivers use a 1700 kc IF, which results in a bit of 
offset between bands. If you have the xtal and IFTs, however, there's no 
reason youcan't use 1750 kc. as the first IF, which puts 3500 and 7000 at the same 
place on the dial. VFO tunes 5250-5750 to cover 3500-4000 and 7000-7500.

But you gotta have an xtal at 1665....

73 de Jim, N2EY


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