[HBR] My Retro-Radio Project...

[hbr@mailman.qth.net]

In a message dated 10/9/03 12:26:49 PM Eastern Daylight Time, 
waltah@earthlink.net writes:


> > I actually "construct" the whole receiver on paper this way, drawing
> > the resistors, capacitors, etc.---EVERYTHING. Then, as I actually do
> > the soldering, I highlite each part on the paper as it is soldered
> > into the actual circuit ... Does anyone else use this technique in
> > building? 


I do, sometimes. Depends on the project complexity and how much I'm trying to 
stuff in a given space. 

> 
> No, and I admire your use of it -- this is clearly better than the way I 
> do it.   
> 
> I spend hours playing chess with the large parts on top of the 
> chassis to get the signal paths right, get the right stages next to the 
> panel (for controls) and hopefully keep things that will interfere well 
> separated.   I try to stretch the main signal path all across the 
> chassis, wrapping it around uncritical stages, chiefly audio and  
> power supply.   Things that make heat are separated from things that 
> are heat sensitive -- tubes are away from VFO coils/capacitors and 
> crystals; power resistors and output stages are kept away from filter 
> caps.  If things start to seem 'tight,' that usually means a larger 
> chassis is needed.   

I do that too. Helps to cover the chassis with graph paper (I use rubber 
cement). 

> 
> What does the panel look like?   Is it reasonably balanced?   Can the 
> controls be reached?   Will the panel controls interfere with the 
> chassis?


'zactly. 

> 
> There are the usual issues of capacitor gangs hitting stuff, meters 
> poking through the panel into a tube, and so on.   Then I look at 
> tubes that I know  will have more parts -- low level audio stages, plate 
> detectors, and the like -- they need extra space.   Where will wires 
> go through the chassis?   
> 
> Lots of space is needed near the plate transformer for terminal strips 
> and filter caps.   Speakers should be given extra space because you 
> rarely (these days) can find a duplicate if they have to be replaced.
> 
> Then I orient the tube sockets to place the grid and plate pins in line 
> with the signal flow.   
> 
> Finally, I try to think of the things I *might* do, and leave extra space 
> to make it possible.   For example the 1MHBR has ample space to 
> add  a 1665 kcs IF stage and the added hole needed for the larger 
> plate transformer that will be needed, is already drilled.   I didn't at 
> first think I'd use a trimmer on the antenna circuit but I left space and 
> later installed one.  I left a little extra space between the front end 
> tubes and the tuning cap for a heat shield -- and the other day used it 
> to install a substantial heat sink plate under the tubes.
> 

Always good to go a little bit bigger than a little too small.


> There are always things I didn't think of.  I admire anyone who carries 
> the process to actually sketching out the locations of the small 
> parts.   
> 

Here's another trick:

Most major projects I do wind up being prototyped to prove out the circuits 
and sometimes components. For example, when I first got the filters used in the 
Type 7, I had no idea if they were any good, so I built a prototype 80 m rx 
to try them out. While testing said rx, the first station I heard was master 
builder W2LYH, whose projects I had admired for 25 years but who I had never 
encountered before. I flipped on the main rig and worked him. 

The filters are excellent, btw. 

Now THAT's a good omen!

Prototyping here is done with modules made of scraps of aluminum and PC 
board. Each stage or functional block is built on a small (couple of inches square 
or rectangle)  scrap of aluminum sheet or PC board, becoming a module of that 
stage. Long screws in each corner of the module act as "legs" to keep its 
bottom off the table. Holes around the edges permit bolting modules together as 
the project progresses.  The result is quite odd looking but goes together fast 
and does the job. If a stage needs to be added or removed, the modules are 
unbolted. Controls are stuck in wherever practical. Power and control lines daisy 
chain from module to module. No front panel is needed in most cases. 

Often a module from a previous prototype is recycled to a new one. 

The parts used in the prototype modules are usually used-but-test-good. 
"Nice/good" parts are tacksoldered. Thus those old paper caps and carbon comp 
resistors which still test OK have a use, without taking a chance on being used in 
a serious project. 

Yes, there's a shock hazard, but it is minimized by keeping the HT below deck 
and the controls above deck. 

I use external power supplies in almost all my homebrew stuff.  This not only 
reduces heat, size and weight, but also saves time and having to hunt for 
power supply parts. By standardizing the power supply connections and voltages, 
the same power supply can power a bunch of different projects. 

73 de Jim, N2EY


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