Roger, if you look at the AM and some other forums you will find home brew
is alive and well. Those hams dont need $1000 tubes to make power and are
mostly making do with glass bottles of the past with some maybe going a bit
beyond the 1500W PEP rule. But nobody really cares as these guys are as
clean as they can be and are really not running any more power than what was
legal in the 1KW input days.
A problem with many potential SSB amp builders is that they are brainwashed
into believing that they have to either buy the best Eimac has to offer or
suffer thru the IMD generating junk out of Russia unless they run 75-80% of
Pd as idle current. Even Chinese copies of Eimac are no bargains any more.
The potential builders also feel that they need 2000-2500W of keydown
capability to be competitive as shown by most of the current crop of
commercial amps with many going above that. A few on here whine when someone
suggests a YC-156 but say nothing about the multi kilobuck in a box amp.
BTW, the YC-156 filament is 175W, thats a huge 25W over a pair of 3-500Z's;
it does take 8 minutes to warm up tho and a bit of skill to get it on 10M.
At the low end there is an unlimited supply, it seems, of Heath, Dentron and
some small Ameritrons amps in particular for way less than the current price
of 1500-1600W Pd worth of just the tubes. Toss in all the thousands of old
Henry floor amps that nobody with a new ricebox wants to be seen with.
Love them or hate them, there are many glass and ceramic tubes out there of
older design that are downright bargains that will easily give 500-2000W +
out. Most dont die if you look at them wrong either....thats another plus
for the YC-156.
Older 115 or even 230V iron will still work, its just not going to be a
table top amp and dont expect 1500W out from a 120V 15A breaker either. Run
a new 30A service and quit worrying about it if you find a 3kva monster for
free or cheap. So what if you might have to use a choke input; the peak
output of the transformer can still be obtained. Tuned chokes work fine if
done right. Get creative for QRO and run a cheap 208V 3 phase transformer on
240V single phase; it can be done and with reasonable efficiency. If the
price is right........give it a thought. Pole pigs are also still available
and work just fine on 120V for many tubes.
When I was on this forum in the 90's home brew was the norm for members and
not the exception as it is now. What went wrong?
Carl
KM1H
----- Original Message -----
From: "Roger" <sub1@rogerhalstead.com>
Cc: <amps@contesting.com>
Sent: Thursday, March 25, 2010 3:56 PM
Subject: [Amps] Why people don't build amps.
> The reason for homebrewing is a slight, but valid turn from the original
> direction of the "Good Engineering" thread,
>
> There are many reasons for people not home brewing and the fear of
> failure is just one and I doubt the major reason.
> Today's crop of hams coming up are not (in general) as technical minded
> as those of earlier days.
>
> In days gone by we built often from necessity. There were lots of
> sources for parts, not the least was surplus and cheap/inexpensive
> surplus at that.
>
> My first transmitter was the pair of 6L6's with a 6AG7 Oscillator built
> on the corner of an old TV chassis. It was big, ugly, and it
> worked...well...after I discovered you don't use wire wound resistors in
> those circuits. Oh! and it was cheap as IIRC it was all from used parts.
>
> Since that time I've build a number of amps, Yagi antennas for 20 and
> 15, but the source for parts is drying up and what's left is getting
> expensive. When I became a ham I had a stack of large and heavy catalogs
> with almost anything I needed.
>
> If I want to build something, I don't want to spend 5 years (or more)
> hunting through swaps looking for transformers, tubes, and band
> switches. What are the sources for inexpensive transformers that will
> do the job? Not microwave ovens, those things get hot and are not
> designed for continuous operation. OTOH if one is willing to put up with
> their short comings they can be paralleled to provide power for a medium
> size amp.
>
> Another reason for lack of building, at least for people like me, is
> when it's finished I don't want it to look like something some one
> cobbled together. In that vein I'm a bit of a perfectionist. Plus if
> you have to purchase the parts you can likely go out and buy the whole
> amp for less money AND have something with a reasonable resale value.
>
> Now I see the legal limit brought up when tubes of substantial ratings
> are brought up, but it really has nothing to do with legal limit. For
> instance, those rugged triodes should not be written off, and the more I
> think about it the more I think if I built another amp that's what I'd
> use and why not? Well other than the power it takes to light the fire
> inside that is. Look at the characteristics of those tubes. See what
> they take for drive? IOW most of todays rigs with only a couple
> exceptions are not capable of driving those tubes any more beyond the
> legal limit than the AL1200 and 1500 can go. Besides, when run at that
> power level they don't take a lot of cooling. Some of them don't even
> require a socket making the construction of the amp more simple.
>
> People don't build because they have no desire to do so, or they see
> they can purchase an amp ready to go for the same or even less money
> than building one. Then there is the lack of metal working skills. I've
> seen very few amps that were home brew that didn't look home brew and
> I'm being very courteous referring to the appearance. Want to change or
> upgrade later on? You'll be lucky to get the value of the parts out of
> it, but then again, you might actually find some one who wants it.
>
> However I do think there is some fear when some one looks at spending 3
> or 4 thousand dollars to build a rugged, legal limit amp capable of TRUE
> "brick on the key" 24X7 such as digital, or long winded AM operation.
> None of this brick on the key sending a series of dots for 24 hours.
> Depending on the weighting, that could be any where from 50% duty cycle
> to 30% or even less.
>
> But lets say you have access to one of those ultra linear 3CX or
> 3CPX5000 pulls with fantastic IM in the minus 50 db range, that can
> comfortably run the legal limit using all of the drive from your 100
> watt exciter. You only need a plate supply capable of about 3000 watts
> if you figure 50% efficiency AND want the key down 24X7 CCS , or you are
> going to be operating...<gasp> AM. There is absolutely nothing illegal
> or unethical about this approach. Although big, this could be built
> into a desk top amp maybe slightly larger than the the EMTRON DX-3SP
> although squeezing a 3KVA plate transformer and 350 watt filament
> transformer in there along with the rectifier and capacitor banks may
> take some doing.
>
> Winding the tank coils is easy, but may require sacrificing some copper
> tubing while learning, or you can find some one who is good at winding
> coils. Given the plate impedance, you should be able to find a design
> to copy which makes placing the taps on the coils much easier. Also
> good hefty toroids for the 160 and 75 meter bands is now the way to go.
> I've lost track of how many coils I've wound, but that used to be part
> of my job with those induction heating generators so it's many thousands
> at least and no, I don't want the job.
>
> So if the builder is like me and wants the thing to look well
> constructed in addition to working well, figure in at least redoing the
> tank coils and cabinet about twice. But even neglecting that and getting
> everything right the first time, the power supply alone is going to cost
> more than most entry level amps. I'd guess by the times it's finished
> and working the amp is going to cost about as much as the top end
> Ameritron, or maybe Palstar but it will be rugged and something to be
> proud of.
>
> Now, how many people do you know that would spend as much as an AL1500
> costs to build an amp when they can purchase one for the same price.
> Granted they can build a better amp, but still...
>
> Now lets go back to that legal limit issue. I'm not condoning illegal
> actions, but what is really more ethical, running a 2 or 3 KW amp with a
> very clean signal, or some one trying to push an amp way beyond it's
> capabilities you can hear 10 to 20 KHz up and down the band. That over
> driving along with the speech compressor turned to max is a common
> practice on virtually all HF and 6-meters. There is a faction that will
> crank every thing up for just a few watts that were it clean would never
> be detected on the receiving end. Instead of getting louder they just
> get broader. In my case my voice actually benefits from a fair amount
> of compression, BUT when out in the shop all any one would hear between
> words would be the fans and equipment running in the shop. It basically
> sounds like a huge turbine running in the background if I us much if any
> compression.
>
> Many times when the bands are open I often think we are lucky that more
> hams do not run QRO, or try to push a few more watts out of what they
> have.
>
> 73
>
> Roger (K8RI)
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|