[HBR] HBR-11/2000. Comments?

[Tuchueh7 at cs.com]

First of all, many thanks for the comments fellas. My motto as a good Navy 
man is:
"Fear God and dread nought" Also "A coward dies a thousand deaths, a brave 
man dies but once". Age here is 54, been messing with electronics since the 
early '60s.
I have a background in field engineering; was privilieged to work in the last 
Apollo mission and development of Space Shuttle. Served in the Navy on a 
frigate out of
Yokosuka, Japan as an engineer and electronic material type. Worked in the 
medical
electronics/radiology field and lately have begun fiddling around with Ham 
Radio. Got way too much junk here with vacuum tubes - you know the story.

Let me tackle Jim's comments first:
1) Sketching of layout - Amen!!! Big weakness of mine, never understood what 
was meant by "measure twice and cut once"
2) Double tuned preselector - A tunable bandpass filter either top-coupled 
with a carefully calculated cap (calculated for the mid-frequency) or bottom 
coupled with a mutual inductor - - need to consider this very carefully. 
Compromise here will be decreased performance at either extreme of tuning range. Will 
breadboard an example and check it out.
3) Inadequate RF gain - Maybe, but my thinking is low gain at the beginning 
simplifies
the dynamic range problems. Gain distribution in receiver design is a major 
consideration. A low noise low gain front end can be compensated with higher 
gain
further into the receiver, yes?
4) I chose a Vackar L.O. cause of the mystical belief of its superiority at 
higher freqs!
I also like the fact that the tube is swamped out of the tuned circuit by 
large capacities; I intend to use polystyrene caps for these swamping capacities. 
I have the
references you mentioned and will look into them. 
5) 6AR8 was selected in order to preserve the limited quantities of 7360 for 
the classic gear. Also the dynamic range of this single balanced mixer 
configuration was
considered.
6) 6EH7 is a devil. I breadboarded a 6AR8 followed by one standard IF stage 
using some Meissner-looking 455 kc. cans. Peaking the IFs for max was 
impossible. Never-the-less these two bottles gave me 70db of gain and great 
selectivity. This is on a sheet of green epoxy perfboard! I am thinking with a real metal 
groundplane and attention to detail its doable with the Miller 710s. Time 
will tell.
7) 6BN6 was chosen for its limiting capabilities. Got some rubber shockmounts 
for the socket.
8) I think that AGC circuits could stand a lot of improvement. I have yet to 
see one that can really track all of the mischief that the ionosphere 
inflicts. I am thinking that
a really sophisticated analog computer could servo all of that 6EH7 gain. 
Need to resort to solid state opamps because of the sheer volume of circuitry 
here. Would like to advance the state of the art.
9) 5879 is engineered for audio. I want lots of audio gain to waste with 
heavy negative
feed back. The audio section is going to meet communication specs - low 
distortion,
narrow bandpass for voice and lots of power. Would also like to keep the heat 
down.
10) Solid state regulators for the oscillators plate supply. also regulated 
DC for the oscillators filaments.
11) Plug-in coils do simplify things greatly, but so do reed relays. They are 
a mature
and reliable technology already used in the best radios. I also got a great 
big bag of them on the surplus market at a buck apiece. Toroids are small, 
hi-Q, inherently shielding and I have found the the 2 and 6 mix to be reasonably 
stable, when in a constant temperature environment. Bandswitching is one 
feature that I need for my
operating style, so I will make an effort here.
12) Variable selectivity - again, this is a communications, ham-band radio. 
Three kc.
suits me just fine, and a Q-multiplier would be desireable. Also, IF 
regeneration is a possibility. No mechanical filters for this kid - after all this is 
an HBR. I would like to
stay reasonably close to tradition
13) Tuning cap - three gang, I have a number of candidates here. I will send 
more
details and pics later on down the log.
14) Oversize chassis - Amen! Many of my projects have fallen by the wayside 
because of my failure to visualize or inability to modify my way out of a blind 
alley.

Again, my thanks for the comments. 73s      Barney