[Amps] Good amp to buy maybe build..

[Roger]

Bill, W6WRT wrote:
> ORIGINAL MESSAGE:
>
> On Sat, 30 Jan 2010 23:25:23 -0500, Roger <sub1 at rogerhalstead.com>
> wrote:
>
>   
>>>   
>>>       
>> You can't say that about airplanes though.  Due to the certification 
>> process of commercially produced aircraft you can build one far cheaper 
>> than you can buy plus if you do a good job on one that is a desirable 
>> model you might likely sell it for twice what you have in it.
>>     
>
> REPLY:
>
> When you say "what you have in it", how are you valuing your time?
>   
In that case, yes.  Even if you figure $30 per hour at 4000 hours build 
time  that's $120,000
parts are about $75,000 to $175,000...so figuring the high end for 120 + 
150 = $325,000 some of those planes are selling with the test hours 
flown off, for a half million or more. Some of the newer ones with 
turbines are running well beyond that.  The G-III like mine which are 
2-place and unpressurized are less, but they run such a high wing 
loading it's like flying a P-51. So the market isn't nearly as large and 
the number of capable pilots is small. They are a joy to fly, but 
pulling the power back and seeing 2200 to 2500 fpm as a rate of descent 
is far higher than most pilots of small planes see and it's a figure 
that can be both overwhelming and more than a little scary as is coming 
over the fence at double or more the speed they normally see.

When it comes to amps, the builder should know what they want and their 
design goals (including quality). The number of parts is relatively 
small. The transformer is the largest expense with the tube being second 
largest although depending on the tube those can swap places. Some times 
a pole pig (which is big) can save the builder some big bucks, but it 
means an external PS.  Put it on wheels and roll it under the desk.  
Taking an amp from the handbook or using someone else's design that has 
been documented, laying out the parts list, doing the research as to 
prices and best places to buy (BEFORE) starting the actual work, the 
cost and hours to be invested can be minimized.  Building even a high 
power amp is much easier than building a transmitter or receiver, but 
you need to know where to get things. Like any project you need to know 
what you need and where to get it or who can get it for you and then go 
from there.  That's all there is to managing a project.  BTW if you 
build 2, you can do the second one cheaper and in less than half the 
time. <:-))

Purchasing can be new, the best, the cheapest, surplus, or hamfest 
scrounging.  In the long run overall, the hamfest scrounging can be 
(although not always) the most expensive when your time is figured in. 
If you are very lucky it can be the cheapest too.  The odds are that 
it'll make the project take several times longer than purchasing new parts.

If you take a look at the old Alpha 76 it's all square parts for the 
metal work. Simple, and easy to put together.  The only forming I 
remember is the top which is a U-shape with the edges broken to 90 
degrees. Simple to make even with home made tools.  The front panel is a 
simple rectangle with square cutouts for the meters and most of the 
switches. Band switch, tune, and load are simple holes drilled through 
the panel. Fast if you have a CNC mill, not bad with a regular mill, but 
requiring a lot of filing if done by hand. Go with meters that take a 
round hole,  that are front mounted, use toggle switches and the panel 
just became a lot simpler still, although not as professional looking.  
If that wasn't part of the goal, then who cares?   Most of the internal 
metal work is relatively simple too.  Although I don't know which 
Aluminum they use, it's one of the harder alloys which is relatively 
easy to drill. Most hams use the same kind of aluminum you find in the 
old chassis we used to purchase and of which I still have a bunch. It's 
too soft and although some claim to drill it without burrs I have to use 
drill bits specifically sharpened for that material as the Titanium bits 
just don't do it for me.  T-6061 which is used for aircraft skin is hard 
and relatively easy to work with and it's the one I prefer even if it is 
about twice the price of the softer stuff.
BTW I happen to like the "fly cutter" when used in a mill. I've had 
excellent results with them except on dead soft, thin sheet.
IOW the metal work is mostly flat pieces including the front and rear 
panels. This reduces the time and effort to build the thing.  Then it 
becomes a kit without the mechanical dimensions. Purchasing in small 
quantities is still going to raise prices, but there isn't a lot 
there...UNLESS you use a fragile Tetrode that requires a lot of 
circuitry to protect the tube. Even an expensive 8877 can get by with 
minimal and relatively simple protective circuitry. 

Not all the Russian tubes are class C junk but if going that route you 
need to know which are and which aren't.  IF the tube or tubes are used 
in commercial amps then you can be fairly confident they are a good tube.

So there are many ways to save money when building an amp.  As I build 
for fun, then quality is paramount to me. However the person who builds 
for functionality and gets an amp that works gets just as much 
satisfaction as I do.  Our goals are different and neither one of us is 
likely to save anything over a commercial amp.

73

Roger (K8RI)
> 73, Bill W6WRT
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