Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Building a new amplifier




 
The AM Forum
October 01, 2023, 06:17:45 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: 1 [2] 3 4   Go Down
  Print  
Author Topic: Building a new amplifier  (Read 62666 times)
0 Members and 1 Guest are viewing this topic.
ka1tdq
Member

Offline Offline

Posts: 1508


I make stuff


« Reply #25 on: December 05, 2015, 03:48:15 PM »

Ah, good stuff... and cheaper too!  God bless the Chinese.

Jon
Logged

N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #26 on: December 05, 2015, 04:49:13 PM »

I doubt you will need much cooling running three at 350 watts carrier.
I have three 4-400's in a rig I screen modulate and it does 400 watts carrier with almost no color showing on the plates and very little air flow.

A good rule of thumb is 1/3 of the plate dissipation for power output, which in your case would be 500 watts.
Under that, gentle air flow should be fine I would think.
Logged
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2592


Making AM GREAT Again!


« Reply #27 on: December 05, 2015, 05:03:25 PM »

Mayanoisse,  pickle and other jars can work as well.

A piece of string,  lighter fluid,  match and sink can cut to height.

With the added benefit of having a taper at the top.

With your having a complete two tube box adding a third was the best way to go.

With the added dissipation,  make sure you run the carrier up,  or at least the bias,  from time to time,  to blush the plates and getter your tubes.

PVC makes GREAT air director material.   No corrugated means max airflow through it at minimal noise.



--Shane
KD6VXI
Logged
ka1tdq
Member

Offline Offline

Posts: 1508


I make stuff


« Reply #28 on: December 05, 2015, 05:46:13 PM »

I have a quiet bathroom squirrel cage fan with a 4 inch duct that I will use to pressurize a box below the tube sockets.  I'll just go ahead and do it right.  I'll make it so that I can put a filter on the intake to minimize dust buildup.  I'll also minimize components inside the box so that they don't collect dust.  I also have to make the box serviceable so that I can get into it once a year to remove dust.

The RF deck will be built on a steel 19" shelf and I'll cut a square hole to accommodate the 3 tubes, plus a little extra.  I'll then mount the box to the bottom of the shelf.  This would make things convenient in the future should I decide to use different tubes.  Just remove the box.  

That's a good idea about making sure the plates blush.  Either increase the bias on the cathode or run more carrier.  There would be a limit though for bias before you run into linearity problems.  Maybe 10 volts maximum.  My transmitter puts out 24 watts carrier, but I could adjust that if needed.  

These Chinese sockets/jars are cheap enough that I'll just go with them.
Logged

KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2592


Making AM GREAT Again!


« Reply #29 on: December 05, 2015, 09:17:52 PM »

I've run a 500Z to 50 mils of resting current,  sometimes even lower,  for am operation.   The trick is to make sure you have enough carrier to make sure the tube self biases up to at least class B.

At 3.3kv, about 20 volts is good for the 500z.

There is a good thread about this,  started by Tom K1JJ iirc,  about this operation.

Honestly,  though,  having 3 tubes means you won't really need to worry about efficiency from a Pdiss standpoint.

I've seen 10 and 12 tubes on ten meters.   Three will be easy peasy from mf to 40.... 

--Shane
KD6VXI
Logged
DMOD
AC0OB - A Place where Thermionic Emitters Rule!
Contributing
Member
*
Offline Offline

Posts: 1744


« Reply #30 on: December 06, 2015, 11:39:03 AM »

I run 11V bias and 3600V in my Henry 2K-4.

Here is the PS Schematic in case you might be interested:

Phil - AC0OB


* Henry 2K-4 PS Mods for AM Phone.pdf (736.88 KB - downloaded 413 times.)
Logged

Charlie Eppes: Dad would be so happy if we married a doctor.
Don Eppes: Yeah, well, Dad would be happy if I married someone with a pulse.NUMB3RS   Smiley
ka1tdq
Member

Offline Offline

Posts: 1508


I make stuff


« Reply #31 on: December 12, 2015, 09:46:54 AM »

Here is a picture of the HV power supply under construction.  I wanted to build the power supply separately from the RF deck to make things simpler the next time I want to build something different.  Also, these will be just small enough to be rolled in/out of the walk in closet adjacent to my radio room.  This adds a little extra security by being able to be locked behind a door.  Obviously though, the closet door will need to be open for air circulation during operation. 

The blue lights on top are visual aids.  One indicates when blower/filaments are on and the other when HV is energized.

The RF deck will be a welded steel frame structure with metal on all sides, except for a plexiglass front. 

Jon


* IMG_1476.JPG (866.95 KB, 2048x1536 - viewed 912 times.)
Logged

W3RSW
Contributing
Member
*
Offline Offline

Posts: 3308


Rick & "Roosevelt"


« Reply #32 on: December 12, 2015, 03:59:12 PM »

Massive. I guess you'll enclose with mesh or perforated sheet metal.

Say, who're the good looking pair with sun glasses in upper left of Pix?
Logged

RICK  *W3RSW*
ka1tdq
Member

Offline Offline

Posts: 1508


I make stuff


« Reply #33 on: December 12, 2015, 05:52:40 PM »

Plywood. I'll leave a small air gap in the back. The front will have padlocks on the switches as well as a 240 service box with a padlock. The RF deck will use massive amounts of steel.

The good looking person in the photo is my wife. I was just along for the ride that day. She likes me because I'm a Ham radio operator. Hams are studs.

Jon
Logged

KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2592


Making AM GREAT Again!


« Reply #34 on: December 12, 2015, 07:35:42 PM »

A small fart fan,  very low sonne,  in the top of your closet would probably be capable of exhausting your hot air.....

At least that created by the amp.   The hot air the amp amplifies,  that's the antennas job :-)

--Shane
KD6VXI
Logged
flintstone mop
Contributing
Member
*
Offline Offline

Posts: 5055


« Reply #35 on: December 12, 2015, 09:45:18 PM »

Hi Jon,

After watching you put the last 3-500Z amplifier together with 2X4s I figured it would only be a matter of time until you tore it down and started over...  Grin   I've done the same thing in many different ways.  

Check out the YC-156 tube. It's similar to a 3CX-5000A7 but slightly different fil requirements.  Both amplification factor of 200.  No socket required and uses 225 watts to light the fil and is probably the cleanest tube on the market. They used it for precision MRI work.  

With 3.5 KV on it, you can run it VERY conservatively at 2500 W out and achieve a 3rd IMD approaching -45 dB or higher, depending on how good your driver is.  CLEAN!   It's like an 8877 on steroids.  It would just laugh at AM KW service.

I know of someone who may part with a good pull since he never built an amp with it yet.

T

I knew someone would post a tube with HANDLES

Fred
Logged

Fred KC4MOP
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8242



WWW
« Reply #36 on: December 14, 2015, 01:33:52 AM »

That's a nice sturdy looking cabinet. The power transformer - a serious 2KVA one? very nice.  There's one like it here, a beast.
Will you use the blue CFLs to light the inside of the amplifier cabinet?
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
ka1tdq
Member

Offline Offline

Posts: 1508


I make stuff


« Reply #37 on: December 14, 2015, 05:08:09 AM »

I've posted another picture of further progress.  What's left to go on front is switch lock covers for the switches and a voltmeter on top. 

Yes, the transformer is 2kva. 

It's tempting to put CFLs in the RF deck as well.  But from my last amp, the glow of the tubes is just the right touch.  Especially now since I'm going to use 3 tubes rather than 2.  But, I guess you could put a couple in not connected to power.  That way, when you transmit, the room glows even more!  But, as G.W. Bush used to say... "Na - ga - doit."

Jon


* IMG_1677.JPG (1786.59 KB, 3264x2448 - viewed 771 times.)
Logged

N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #38 on: December 14, 2015, 09:43:48 AM »

Looks like a fire hazard...
Logged
ka1tdq
Member

Offline Offline

Posts: 1508


I make stuff


« Reply #39 on: December 14, 2015, 11:18:22 AM »

True.  Steel framing would've been safer, but it's a manageable risk.  It's always good to have a fire extinguisher in the shack.

Jon
Logged

w1vtp
Member

Offline Offline

Posts: 2638



« Reply #40 on: December 14, 2015, 12:41:06 PM »

True.  Steel framing would've been safer, but it's a manageable risk.  It's always good to have a fire extinguisher in the shack.

Jon

I like it.  Just keep that fire extinguisher handy   Grin
Logged
K1JJ
Contributing
Member
*
Offline Offline

Posts: 8869


"Let's go kayaking, Tommy!" - Yaz


« Reply #41 on: December 14, 2015, 02:20:46 PM »

Over the years, building many homebrew rigs and shaking them down in testing, I've had plenty of fires.  Resistors flame, capacitors blow, wires arc over and flame, transformers overheat, wire fuses arc and catch the surrounding stuff on fire, spark gaps get unruly, etc.  It does happen to all active home brewers at one time or another.

Using a metal cabinet is the best method. A second alternative is to line the critical areas inside with some aluminum sheet.

In your case Jon, at least put a smoke detector in the cabinet.  I use a couple in my shack above the rigs just as a precaution.

(I even got rid of all the Plexiglas and went to all steel / aluminum cabinets)

T

Logged

Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
Steve - K4HX
Administrator
Member

Offline Offline

Posts: 2722



« Reply #42 on: December 14, 2015, 02:29:04 PM »

Logged
ka1tdq
Member

Offline Offline

Posts: 1508


I make stuff


« Reply #43 on: December 14, 2015, 02:36:48 PM »

That's a good idea! It'll give you a head's-up if something starts to smolder.

Jon
Logged

N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #44 on: December 14, 2015, 04:03:56 PM »

The rf might set it off.
Logged
ka1tdq
Member

Offline Offline

Posts: 1508


I make stuff


« Reply #45 on: December 26, 2015, 06:37:43 PM »

The power supply is 95% done.  I've attached a picture.

I was on the air yesterday and someone from Tucson heard me talking about the new amp.  He has a 17 x 17 x 7 unmolested aluminum chassis that would work perfect.  I'm heading down next weekend to pick it up.  It should fit 3 tubes nicely.  I still need to weld together the steel structure it will sit on.  It's perfect for the RF deck, but I still need to pressurize the bottom of the tubes and enclose the bottom "stuff". 

So, yeah... people can still hear you with 20 watts carrier!  :-)

Jon


* FullSizeRender-11.jpg (1191.46 KB, 2423x3230 - viewed 795 times.)

* IMG_1699.JPG (1517.76 KB, 4000x3000 - viewed 904 times.)
Logged

N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #46 on: December 26, 2015, 07:17:53 PM »

No stain on the wood?
A nice harvest color with clear coat would look nice...
Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8242



WWW
« Reply #47 on: December 26, 2015, 09:25:19 PM »

It looks good. Yes some finish and it would look like furniture.
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
ka1tdq
Member

Offline Offline

Posts: 1508


I make stuff


« Reply #48 on: December 27, 2015, 04:36:33 PM »

Okie-dokie...


* IMG_1703.JPG (1781.79 KB, 3264x2448 - viewed 838 times.)
Logged

N2DTS
Contributing
Member
*
Offline Offline

Posts: 2307


« Reply #49 on: December 27, 2015, 09:51:42 PM »

There you go, now maybe add some brass hardware, or at least paint the electrical boxes gold hammertone...
Logged
Pages: 1 [2] 3 4   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.089 seconds with 18 queries.