[Amps] building amps.

Fri Mar 26 08:00:44 PDT 2010

Date: Fri, 26 Mar 2010 01:58:27 -0400
From: Roger <sub1 at rogerhalstead.com>
Subject: Re: [Amps] Why people don't build amps.

Cecil Acuff wrote:
>>
>> What are the sources for inexpensive transformers that will
>> do the job? > ----------------
>
> Interesting post...I have some of the same questions.  Options for 
> inexpensive, reasonably sized plate transformers?
Carl came up with some such as pole pigs. Another would be old 
commercial repeaters that had amps built in. I'd guess some of those 
transformers would be good for about a KW PEP out. Of course the pole 
pigs are big and heavy, but there's no rule the transformer and PS has 
to be in the same cabinet.

##  Put the HV supply on the floor, where it belongs, or the bottom
of a small 19" rack.  If you do buy a new dahl/harbach xfmr, get LOTS
of taps. BTW, you can grab ANY 2 x sec taps.  My dahl is tapped for
0-2300-3900-4800-5200   I  was upset, cuz I forgot the 2900 tap. 
Well 5200-2300= 2900 !  Knowing that info.. I would carefully spec taps
Also, having a 220/240  or  230/240  pri is a great asset.   Then, between
pri and sec,  you have literally loads of combo's.  Buy one big xfmr, then you
can use it on ANY amp, with voltages  from A-Z.  A  46 lb hypersil  runs $400.00
which is what`s used in the alpha 77dx/sx.  Now  $400-$600  may seem like
a lot of $$,  but it's the most important part of the amp !  power starts  with the
xfmr.  $400-$600 is cheap.. compared to the $8-9K   alpha wants  for the same thing.

##  you can always get all your money back on a dahl xfmr, and then some... or
just pass it on from father to son. 

##  I paid $75.00  for  my 10 kva  4160/4800  hypersil pole pig, 120 lbs, just
under 1 cubic foot.  You just can't blow it up.

## arnold howell, from howell tube sales has access to a LOT of pole pigs.
Smallest ones are 5 kva.  He also has 2 x doz  YC-156's [ youngstown ohio]  

>
> -----------------
>> 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.

## Roger.  with 100 w of drive... you will send a YC-156 way over 1.5 kw
maybe 25-40w max. 

> ----------------------------
>
> Can someone provide sourcing info on reliable, reasonably priced pulls 
> for home builders to build with?

##  www.ctrsurplus.com   YC-156's   $125.00   [419] 683-3535
if u dilly dawdle, you will lose out.. and probably have by now. 

> Would love to buy a couple Triodes that don't require sockets.  Would 
> even consider tetrodes.

  Another place 
would be http://www.wa8wzg.net/forsale.htm which has been posted before. 

## he's good too. 

>
>> 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'd dump any notion of using torroids on a HB amp.  They  run way too hot
and u have plenty of room.   I have not wrecked a tubing coil..yet.  Tubing comes in
15-25-50' rolls.   They are very easy to wind.. and silver plate  with cool-amp. 

## Most of us use GM3SEK's  PI  spead sheet.  Then u can design the entire
amp in abt 1/2 hr flat.   I use a B+k  875-B  [ mouser]  to dial in the taps..
dead on the 1st time around.  u want 2.6 uh.... well the meter reads down to .1uh
Toss the GDO, it's useless for taps.  

>
> > What about no band switch and no tapped tank....just a large edge 
> wound roller inductor? 

##  I use a new RI-40  from SSON.  $245.00  on my  3CX-3000A7
0-40 uh, tapered pitch at one end, and uses 3/8" edge wound silver
plated ribbon, .072" thick.  4 x gold plated contacts, [2 x per side]
pinch the ribbon.  It's  built like  a tank, no torroids required. 
Handles  5kw+.   Just elevate it off the chassis by 2-4" 

 and at least one of them is 
almost sure to hit one of the resonances for the plate choke.

## Use the rf parts/ameritron choke, or the alpha choke.

> bit more expensive but time and loss of materials to trial and error 
> are expensive too.
##say what ? 

When you take into account the cost of a custom band switch and the time 
to get the taps correct

##  It takes literally 5 mins to get all the taps correct.. and that's if ur
slow.  The lcr meter makes short work of taps.  It's ur #1 tool !!!! 
You are dead with out it.   The 875-B and other's  will read down to
.1 pf.... and  .1uh 

>
> > I have been inspired by the posts of the last several weeks...
Now that I'm really glad to hear.
> to the point where I started looking for suitable cabinetry for 
> building.  Purchased two 19" rack mounted chassis that had contained 
> 900Mhz radio transceiver systems from work.  Should make excellent 
> cabinets for home amp projects.  All aluminum, probably 18" tall and 
> 24" deep.  Will require some work to add and remove some internal 
> compartments but good starts for $25.00.

##  Good.  perfect size. 

Remember too, that with an amp look carefully at how the commercial amps 
are constructed. Most are of a modular construction with a single bottom 
plate instead of building on the old 14" X 18" X 3" chassis like we used 
to do.

## IMO, don't even try copying the no chassis  route.  I'll take a 
hb  17"  x 18" deep  x 4-5"  tall  chassis  any day.  Input and
tuned input  below chassis.. all output kw stuff above chassis.
Put the B+ supply in a separate box.. on casters... on the floor,
where it belongs.  Or use a 4'  tall rack.. with Rf deck at top,
HV supply at the bottom, use casters.  

You might even want to build some metal working tools such as a metal 
brake.
##  I make all the chassis  from flat panels.. all joined with 1" x 1"
angle AL.  Any panel can be removed, or replaced,[ if u wreck one]
.... and put into the drill press, and drilled  from either inside or outside
 etc, then re-installed.   You can even use an old chassis and put a
 clean new AL plate on top,covering all the old holes.
I get all the al flat plates  chopped to my specs.. at local sheet
metal shop. both the plates and the 1"  x 1" are all  1/8" thick 6061-T6.
Easy to drill, cut, etc.  Greenlee now makes combo drill+tap... super fast
to now tap a hole.. all in one motion.   Use SS hardware.  

##  stick the $125.00 YC-156 in there.[ + mating pole pig]
... and a  smile  will come across your face when you realize you just
beat alpha, etc.. at their own game.
The  YC-156  will make the $9K  alpha  look like a sick puppy.  It will
make 4 of em look like sick puppies.  

Jim   VE7RF   

73

Roger (K8RI)
>
> Cecil
> K5DL
>
>
>
>

------------------------------

Message: 6
Date: Fri, 26 Mar 2010 06:22:00 -0700 (PDT)
From: Lee Buller <k0wa at swbell.net>
Subject: [Amps] Why people don't build amps. $$$ and Shop Class