[HBR] Walt's latest receiver

[waltah at earthlink.net]

Bill Higgs wrote:

> Walt, good to hear that your new toy is playing well. Good luck
> with the matching transmitter project! The earliest editions of
> the ARRL SSB for the Radio Amateur had a couple of exciters using
> tuned circuits only, usually somewhat lower in frequency. However,
> an IF bandwidth is an IF bandwidth, and the BC-453 cans give a
> good one when properly tuned. You'll need double conversion, of
> course, and some good filtering to keep the transmitted birdies
> down. A bit of audio filtering in the mic amp will ease your task,
> and you should have a dynamite sounding rig when you're done. 

Ah ... *That* was what I was looking for.  Okay, I'll go find those 
early SSB for ... books.   I'm gradually collecting them all!

What you say does make sense.   I'll make some measurements 
on the receiver later in the day to try to get an idea of the various 
images, adjacent sideband suppression, and so on.   

I'm guessing I'll have to cut off the audio low end a bit higher than 
one would like, to keep the other sideband far enough away to filter 
it at 85 kcs.   

There is a mention in one of the Radio Amateur's handbooks of 
generating the sideband signal at 30 kcs, but I am not going there.  
Also noted, an SSB amp using a class 'A' 807 driving a pair of 
811A's in push-pull -- in the 1953 handbook, I think.   

I'm still collecting parts so there's no hurry to settle much in the 
way of design decisions.   

Everyone knows about Online Metals, right?   They'll cut you a flat 
piece of aluminum to order and they have an excellent website 
interface.   Not cheap -- with shipping, ~$27 for two 8-1/4" x 14" 
front panels just ordered for the new TX project -- but GOOD.   They 
often ship the day I order and they've never screwed up yet.  You 
want the 5052 alloy for working with hand tools, thickness to your 
taste.   I use 0.090".   

https://www.onlinemetals.com/

Start by clicking the 'aluminum sheet/plate' heading.

Antique Electronic Supply has a decent (not great) selection of 
Hammond aluminum box chassies and as reasonable prices on 
tubes as anyplace I've found.   They too often ship the same day I 
order.

www.tubesandmore.com

> BTW, If the receiver in question is the one using the BC-221
> panel, I have a download of the pic on my computer. I'll e-mail it
> to you directly. 

Thanks -- that receiver project was a dead-end, at least 
temporarily.   I ran out of time for what was a monumentally 
complex project and don't know when I'll get back to it.   However, 
I'd still appreciate having the pic.   

> I've gotten back to my own HBR-? after a several month hiatus
> (looks as though it may wind up with 16 tubes, but not an HBR-16
> circuit - a few diodes but NO transistors). Current area of
> construction is the RF amplifier. I'm going to try the 6BZ6 with
> the circuit in Orr's Radio Handbook, but I may revert to the 6BJ6
> as the pin basing is the same in this configuration. Anyone on the
> group tried this? 

Go with a 6EH7.  Designed for TV IF service at up to 40 Mcs, it 
handles overload situations better than anything else I know of.   
It's cheap ($3 from Antique Electronics I believe) and a far better 
tube, all around.   If you already are committed to a 7-pin socket, 
then I think the 6GM6 is the top bet.  

> Also, I'm going to try toroids in lieu of airwound coils; two
> challenges here: Q is apt to be a bit lower, and you have less
> control of coupling between the primary and the secondary. 

Nah ... Q will be *higher* -- say 2-3x higher.   

It is true that the losses in powdered iron are higher than in air.  
However, comparing an toroid and an air-wound solenoid coil of the 
same inductance, the former will have so much less wire that 
copper losses will be a fraction.   Q of 50 is tough on 80 meters for 
air coils but with a fairly small toroid you can get over 100 and if 
you want Q to the max you can use a larger core and get upward 
of 150 probably.   

Control of coupling is somewhat less since winding spacing has 
little effect, but I haven't found it to be a problem.

Incidentally, all the sources tell you that you cannot adjust 
inductance of a toroid by changing the spacing of the turns but this 
is not true.   The truth is you have *only a little* control.   But in 
practical cases, you usually have more than enough to make the 
difference of one turn more or less on the winding, so you *can* 
trim a toroid to an exact inductance if you want. 

Many of the coils of the '1 month HBR' project are toroids; I did the 
tracking by spacing the turns.

When you get a toroid exactly right, a tiny bit of epoxy spread 
along the winding will lock it down.   And you can still remove the 
whole works if you ever want to recycle the core.  

I don't use them for oscillators because the core characteristics 
change with temp -- for that job you need air.   

> Advantages are that they conserve a great deal of space. A
> breadboarding of the tuned circuit with my dual capacitor and 60
> turns on a T50-2 toroid yielded a tuning range of about 3.5 -
> 7.8Mhz, with a good peak (lacking a dip meter, I couple a signal
> generator to the circuit and then read the peak voltage with an RF
> probe - works for me). As I am using the band imaging technique (80
> is the image of 40 with an IF of roughly 1.8Mhz, I may find I need
> a bit of extra selectivity. It'll depend on the final loading of
> the circuits. Hopefully, I can get some B+ to it by the weekend,
> and start testing. 

Yep.   Unless you want to go with the genuine vintage technology 
used in a particular design (Miniductors ...) use the toroids.   Front 
end Q's are a big part of building a well-performing receiver and a 
toroid design can whip the pants off anything else.   

If you are using a double-tuned circuit ahead of the RF stage, you 
could go with a larger toroid for the second circuit.  When using a 
real ham antenna, the first tuned circuit will be so heavily loaded by 
the antenna that the toroid's Q advantage is minimal but the 
second one will benefit from a 75-series core.  

Consider a reduction drive to adjust this preselector -- it will tune 
*very* sharply.  

Walt
KJ4KV