[HBR] HBR form factor - "mods"

[donald haworth]

-Start from the 'back end' of the receiver.  Build a quality audio amp for
the radio.  not that hard to do, really-maybe a 12ax7 into a 6aq5...then
spend considerable time on the detector(s) and agc system.  Proper agc
operation will make the difference between a radio that is a joy to operate
and one that is disappointing at best.  Google 'low distortion
detectors"-Steve Cloutier, WA1QIX, has a remarkable circuit, for am
detection and agc operation.  For the IF, 6eh7's will give very good results
with great dynamic range.  I have had good results with no cathode biasing
and about 70k R for the screen resistance.  This gives max gain, and about
70db of 'control' with agc from 0 to -9 or 10 volts.
-The best mixer I have yet found is a 6me8, second cousin to a 7360.  Very
linear and  overload-proof.  Conversion gain is very good too.  A passive
tuned filter of 2 to 3 stages-depending on frequency...and there you have
it!  Build it in 'modular' form, allowing you to optimize without rebuilding
the whole radio.  As to the dial, I would highly recommend the N3ZI digital
dial.  Read the frequency of the L.O. minus the I.F.  Tune the 'front end'
separately....no tracking issues...just set the LO to the desired frequency
and peak the front end.....
--just a few  thoughts!
Don (wb0rai) in Nashville

On Sat, Dec 18, 2010 at 4:14 PM, Ian Wilson <ianmwilson73 at gmail.com> wrote:

> I posted a few questions about receivers on another list recently, but it
> occurs to me that many HBR builders and prospective builders probably
> have opinions on these topics also. Here's a subset of my questions
> (the context is 3-30MHz tube-only receivers, primarily CW/SSB):
>  - best AGC?
>  - best front end at handling large adjacent interferers?
>  - best product detector?
>
> 73, ian K3IMW
> ______________________________________________________________
> HBR mailing list
> Home: http://mailman.qth.net/mailman/listinfo/hbr
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:HBR at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>