[Amps] Building an Amp 101

[Roger (K8RI)]

On 1/17/2014 10:10 AM, Jerry wrote:
> I have had a long desire to build my own linear HF or VHF amp.  I believe I
> have the electronic technical skills but after looking at some completed
> projects like those on WD7S website, I realized I don't have the skills or
> tools to do a nice job on the mechanical aspects of chassis / sub-chassis
> sheetmetal work.  I guess I could cram it all into an unattractive box
> behind a reasonable looking front panel but is linear amp building mainly
> for those with good metal work capabilities?   How does one break into this
> with limited workbench space other than an electronic workbench?

There are some links to very well laid out amps on here but no one will 
mistake them for commercial built amps.

Starting with the front panel, there are places that will produce a 
commercial looking panel at a reasonable cost.  Not cheap, but what I 
would call reasonable.  They have a soft ware program that lets you lay 
out the panel, send it back to them and they will produce the panel. 
I've done a lot of construction, but I've never been able to use a saw 
and drill to produce professional looking results.

For cabinet work, I'd get a metal brake.  They are not expensive items 
for something rated to work with the Aluminum used in chassis work, but 
again they aren't cheap. Look at www.grizzly.com . They have small ones, 
but it depends on how large a piece you want to bend or cut.  Prices go 
up rapidly with size and can easily cost as much as an amp... or more<:-))

Metal brakes that will handle chassis work are relatively easy to build 
out of steel angle and a rod or pipe to give you leverage.  It does take 
a bit of thought and planning when bending your own to get the 
dimensions correct.  The biggest problem is getting a smooth surface on 
the angle that you then polish if you want scratch free results. The 
only tools needed to build one  are a hack saw and a drill.  Look at the 
designs of the vise brake.  If you have a large and heavy vise mounted 
on a heavy bench (as in welding bench) you can clamp two steel angles 
for the one side and use "C-clamps farther out.  You are still going to 
be limited to not much more than 12" in most cases. Don't make one an 
inch larger than what you will need as they are heavy and going larger 
means thicker steel.  They can be designed to mount using "C-clamps" on 
a "STRONG  and RIGID" work bench. With a frame that bolts to the floor 
they are really heavy.

In the end, most hams will use angle and flat sheets which immediately 
says home brew, but it's so much easier and faster. Plus you don't have 
to take into account the metal thickness as you do when bending the 
material.  Just learning how to bend flat stock and come out with the 
correct dimensions is an art.  IOW You have to tell the supplier the 
dimensions of the sheet so it will have the proper dimensions after 
bending.  Just making two bends in 1/16th sheet can have you off by an 
1/8th inch or more.   It all depends on how much of a perfectionist you are.

The shear would be difficult, or impossible for most to build and as the 
metal suppliers will usually cut the material for little or even no 
cost, it's hardly worth the effort and certainly not the cost.  If you 
can find the blades of the appropriate size and reasonable price it 
would simplify building one, but the forces are such that one even for 
cutting chassis material can be massive and require a tremendous force 
to do the cutting.  Still, having the supplier do the cutting makes the 
most sense unless you plan on doing a lot of metal work.

73,

Roger (K8RI)


>
> Jerry
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