On 1/19/2014 8:20 AM, N1BUG wrote:
On 01/18/2014 03:16 PM, Roger (K8RI) wrote:
There is actually a preferred length, width, and height ratio that can
easily be maintained.
I presume this refers to desktop amps. My early ones were, but
everything today has to be rack mount. No space, so everything must go
vertical.
Either desktop or pedestal.
I had to use rack mounts for years and usually had tow or three 6 footer
setting around.
If you are willing to take the time to learn to use the hand tools
properly, you can build as good a looking amp as the commercial.
This seems to assume the use of new material or at least material in
good condition.
It does, although it sometimes take quite a while to find the proper
material. As I mentioned I have a propensity for hanging on to bits and
pieces resulting in a rather large accumulation of odd ball parts. That
"quirk" comes from many years of doing what you describe.
Often what I can get is previously used with holes, or
scraps that are deeply scratched, dinged, bent, too small and must be
spliced together... etc. I've become very good at altering the layout to
hide defects, but ultimately one only has so much leeway.
As I said in another post in this thread, "You should have seen my 6C21.
<:-))
When defects
in materials can't be hidden, I lose the incentive to do my very best
work. I suppose that's a personal flaw.
As I also said, the important thing to remember is that it works and you
built it. I mentioned the 6C21 amp, but my first transmitter was a 6AG7
oscillator with a pair of 6L6s. I don't remember the driver but it was
probably a 12BH7. It was built in a corner of a steel color TV chassis.
I used the TV's power supply and stuck a 12AT7 TR switch in another
corner of the chassis.
It not only had lots of extra holes, but sharp corners that were kinda
hard on the finish of the old dresser top on which it sat.
It was big, heavy, and ugly, but it worked and ran the legal limit for a
novice back in 61.
Copy
the physical layout of some of the amps with better reputations. You
can design the circuit if you want to, but why "reinvent the wheel" so
to speak when it comes to the cabinet and physical layout.
Wow! If I had to limit myself to using only parts that will fit the
physical layout of commercial amps, I probably wouldn't have any amps.
I'm able to build amps because I am willing to use parts no one else
wants. Often they are big, ugly, or both. But they work fine.
You use the basic layout as a starting point, but there tends to be a
lot of lee way in parts placement. Just try for maximum isolation
between the input and out put and high enough voltage ratings for
components.
BTW you can
purchase the chemicals to alodyne (put that gold color and protective
layer) on the Aluminum chassis for a reasonable price from Aircraft
Spruce.
Interesting. I didn't see them on a quick search, probably because I
didn't know exactly what to look for. But I will do some research and
check that out.
It's a 2 chemical set and I believe requires hazmat shipping, but I
could be wrong about the shipping. Remember, it's Alodyne which my
spell checker refuses to recognize <:-))
Nice thing about paint is it hides all those scratches. You can buff
the sheet Aluminum before alodyning and get a gold, mirror finish.
BTW use a harder alloy than the typical soft aluminum we usually see in
home brew. It's stronger and easier to work with. I use 6061-T6 but
there are better and cheaper alloys available. Ask the supplier for
suggestions. They are often quite willing to help pick the proper
material..
Check around the local airport for an EAA club. They are generally
quite active in building. I had a complete metal hull for a single
engine plane. I'd have to remove the paint, but there was a lot of sheet
6061-T6 in it. I'm definitely not above reusing and re-purposing materials.
Supplier? I use whatever I can scrounge. Mostly 6061-T6 or similar, but
sometimes I score something better. I prefer the harder alloys. I find
them easier to work with and the end result is better.
Agreed!
If you have the patience to build those with simple hand tools, you have
the patience to learn how to use those tools to their limits.
My earlier wording was probably misleading. In those few instances where
I have materials and parts that are capable of looking good, I can turn
out a good looking product.
Although I'm retired and on a pension, I did build up to where I could
purchase new materials. OTOH I'll never lose that desire to save useable
materials contrary to my wife's desire. <:-)). Any more, my left hand is
only slightly better than useless, so that really slows me down.
I was raised on a 60 acre farm and old enough to remember our first
tractor which was a Farmall A. Not much bigger than a glorified garden
tractor today, but it was followed a couple years later with a "C" and
we were able to sell the horses. So I learned to improvise and save by
example when I was pretty young. BTW I was driving the larger tractor
when I was so young, I had to stand on the clutch with both feet and
pull against the steering wheel to get the clutch in. I taught myself
electronics and got a job working in instrumentation. After 26 years, I
quit, went to college, graduated with a BS in CS at age 50. Started on a
masters, but a good job offer ended that quest. So, I went from a farm
kid on a small farm to a project manager for a large multinational
corporation. With this history, I can Identify with scrounging for
materials.
Even though I now can afford new material, I make regular trips to
the scrap bins at the local metal suppliers. You can sometimes find
usable copper and aluminum pieces large enough to produce usable
grounding panels, heat spreaders, and chassis work. I use lots of steel
as well. OTOH I have a small machine shop and do a few small jobs for
neighbors and hams, but mostly for myself. Working with one hand has
sure slowed that down.
I just picked up 3' of 1/8th inch X 3" wide flat stock and 3 24' lengths
of 1/2" #16 square tubing cut in 8' lengths as that fits in my 4-Runner.
At over $70 total that is over 3 times what I was paying for steel just
a few years back. Even at 1 X 1 or 1 X 2 feet the copper is expensive,
but they will often sell it at a third the regular price rather than
sell it for scrap.
Incidentally, Junk cars are going for $350 plus for the scrap metal in
old cars now. 10 years ago you might have to pay to scrap one out. You
were lucky if they'd take it for nothing.
One of my fondest dreams is to someday rebuild my 4CX1500B HF amp into a
form that looks nice. The original doesn't because the only enclosure
available was too small and forced a cramped layout. Meters don't match,
controls are crammed too close to meters, etc. The same could be said
for my 6 meter amp. I've looked into a rebuild several times but the
cost of material and a few parts would be far more than the total cost
of the amp the first time around. Now I remember why I built it the way
I did.
I could purchase new Eimac 8877s for $305 back in the 70's. Now they are
over 5 times that, although the Chinese copies are good at a bit over
twice that.
I prefer the Chinese FU728Fs over the 4CX1500B although I have a number
of each. They are supposedly interchangeable except for the filament
voltage although the screen voltage may need adjusting. A single one
will run 2500 PEP and 2 KW carrier out with 3KV on the plate in an
Emtron DX2-sp. I've forgotten the screen voltage. Use caution though
as the NOS versions suffer from infant mortality. The new ones are
apparently much better. You have to be carefully running them easy as
they will run negative screen current. I'd prefer to run a pair of them
easy as it would take less back pressure and thus, less noise. I used
the amp in the shop which is about 28 X 40 and never noticed much noise,
but I set it up here in the den and in this small room (bout 10 X 10) it
is loud! Works well with a headset though.
Good Luck es 73
Roger (K8RI)
73,
Paul N1BUG
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