[HBR] HB Receiver

[N2EY at aol.com]

In a message dated 8/4/06 6:46:39 PM Eastern Daylight Time, bjtatum at ev1.net 
writes:
> 
>     1. RF front end and first mixer -- A copy of sorts of the Drake 2-B, 
> whereas the RF amplifier covers all bands of interest and the first mixer 
> operates as another RF Amplifier on 80 meters, but as a frequency converter for 
> bands above 80 meters.

A sound approach, but it has the problem of a lot of stages before the 
selectivity. 

>     2. Variable IF -- The variable IF will cover 80 meters as in the Drake 
> 2-B. I plan to use the parts from an R-25 ARC-5 set { a parts unit I 
> cannabilized} to tune from 3.5 to 4.1 MC. My thoughts are to use the OSC. and RF 
> sections of the tuning gang { after pulling most of the plates} and fixed 
> capacitance across the OSC. and RF coils { from R-25} in order to get this tuning 
> range, using a 6BE6 converter tube.
> 
> 


IIRC, the R-25 tunes 1.5 to 3 Mc. That's a rare unit. Or does yours tune 3-6 
Mc.? Either way, a 6-9 Mc. capacitor is a better choice - see below.

A couple of observations:

1) Please DO NOT pull plates from the tuning capacitor! They are 
irreplaceable! Instead, use the capacitor from a BC-455 (tuning range 6-9 Mc.) It should 
work fine for 3.5 to 4.1 Mc. or so. The coils from a BC-454 (tuning range 3-6 
Mc.) will do the job too.

The tuning gang in a 3-6 Mc. ARC-5 is 142 uuf per section, while the one in a 
6-9 Mc. ARC-5 is 62 uuf per section.

2) If you do pull plates on the cap you have, the tuning scale will be very 
nonlinear, because the plate shape is meant for a wide tuning range (2 to 1 
frequency ratio), not the narrow range you intend (1.18 to 1). The BC-455 cap has 
a different plate shape, and you will have a much more linear dial scale.  

Years ago, (1968?) before I knew better, I modified a BC-454 (3-6 Mc.) to 
tune 3.5 - 4 Mc. by pulling plates and adding fixed C. It worked, but the dial 
was very nonlinear - all squeezed up on one end, and all spread out on the other 
end. 

2) Use the OSC and MIXER sections. That way, you can use the trimmers built 
into the tuning capacitor. 

3) The 6BA7 is a better mixer than the 6BE6, if you must use a pentagrid.

4) Consider having a bit more tuning range (say, 3.4 to 4.2, or even more). 
This lets you use a wider choice of heterodyne crystals in the front end. 


 IF output to be 1415 KC as in R-25 receiver. Was thinking about placing 
back-to-
> back 1415 KC IF transformers at output of the variable IF feeding into one 
> low gain stage at 1415 KC followed by another IF transformer. { This is a 
> departure from Drake 2-B where 80 meter variable IF is mixed down to 455 KC}

>    3. Third mixer -- The 1415 KC from IF amplifer would be mixed down to 85 
> KC in a 6BE6 converter tube, using a L/C osc. at 1330 KC.{ Drake went in on 
> low side of 455 KC IF in the 2-B using 405 KC osc.}.


As already mentioned by another, you'll hear the third harmonic of 1330 at 
3990. If you go high side, (1500), the third harmonic will be at 4500. 

>    4. Final IF Amplifier -- Plan to use the 85 KC IF transformers from R-23 
> ARC-5 set. Thinking that one stage of IF using 6BA6 will be sufficient.

OK for gain but not selectivity. The only reason to convert all the way down 
to 85 kc is to get selectivity from LC circuits.

>    5. BFO / Product Detector / AM Detector -- Plan to use 85 KC BFO coil 
> from R-23 receiver and have front panel BFO control. Would like to have 
> selectable detectors and decent AGC, etc. probably borrowing from HBR receiver 
> circuits.
> 

Lots of possibilities.

        These are some thoughts of mine. One question regarding the IF 
> transformers from the ARC-5 sets : Some of them have taps on the coils, I 
> noticed in schematics that second IF transformer has a tap on input coil 
> connected to plate of first stage tube and tap on output coil of transformer 
> connected to grid of second amplifier tube. Are these taps to reduce the gain?

I think they are to reduce the loading and the gain. The ARC-5s have plenty 
of gain as-is. 

 When I use a higher gain tube such as 6BA6 how should I connect these 
> transformers?

Same way. The 6BA6 doesn't have that much more gain than a 6SK7.

btw, I have located my stash of ARC-5 parts. I have a BC-455 tuning capacitor 
you could use. 

73 de Jim, N2EY