The AM Forum

In the WANTED section you will see Tom's disclosure he plans to get BACK ON THE AIR !!

From the looks of things, he's apparently building a QRP mobile rig.

Looking forward to hearing you OM / caw maw

"Wanted:  3 4X1s or 10,000 50C5s"

GL Tom, bunch of us were talking on the air 'bout how much we miss ya.

Having 'JJ back amongst the herd will be HiHiFB indeed. He adds some depth to our childish humor. :) 

Not to mention a big sig!

Tom Vu, is getting busy with his business  again but he and I have been doing stealth on air testing of a new machine. He will be back

Yes indeed! I want to hear more of this.

http://amfone.net/index.php?ind=media&op=file_view&iden=185

http://amfone.net/index.php?ind=media&op=file_view&iden=223

BTW Tom Vu found he has a soft 4-1000A and needs one.

He said QRP   :D

QRP_K1JJ = 1kW

Mr. Vu has been providing plenty of advice to me on my 813 rig since it is patterned off his 813 Maul.  I can't say enough thanks for his help and advice over the many months.  He's found the time in between his new business to lend time to exchange emails with me.  My hats off to him.  He's the quintessential elmer and ham.  Looking forward to hearing him on the air with his new rigs and talking to him with my new rig. 

Others who should be thanked as well:  Timtron/HenryLR and Frank/GFZ. Thanks guys. 

Got some bugs to work out but the 813 rig will be spewing AM RF shortly.

Bob

Thought I heard '185' on the air 'bout a week ago.  Very entertaining. Original recorded back in Japan, Inc. days?

Yo Guys!

HehHeh....all the usual suspects. Yep, I can see it'll be fun getting back on. I missed the action for sure.

I've saved up some good laugh material over the last two years. Even wrote a ham radio game show script that can be held on the air, just like the Limbo "How low can you go" we all used to do on 75M.  The new show is called, "I know how hams think."  Contestants compete and try to anticipate how a ham would respond to a particular situation.  It's all canned questions, but pretty funny. (caw mawn)

Anyway, here's a few shots of the new homebrew 4X1 X 4X1 PDM rig and the 4X1 X 833A's plate modulated rig.  The pdm rig took me a good two months of troubleshooting  get working right. The pdm filters leaked, switch tubes took off, pdm generator was unstable, dud tubes, etc. But now its pretty flat and clean with switching sidebands down at least -110 db.   It's ready to snort fire.  Thanks to Frank/WA1GFZ for his e-mail and phone help. He be da man when it comes to pdm and power supply switching magic and design.

Debugging the 4X1 X 833A's rig was much easier, however. This rig has heavy audio negative feedback for that smooth sound, using 1kw RCA BC iron. I ended up buying a new pair of those wonderful 833C's with the carbon plates for $110 each at RF Parts. Highly recommended. Notice that all rigs are under Plexiglas for our viewing pleasure.


The third new rig not shown is the BLOWN 813 X 813's. This rig is the usual "Tesla 360" design.  The nice feature here is the new WA3KLR designed cathode FET audio driver. It works perfectly and allows up to 10db ++ negative feedback. No transformers, so no neg feedback instability or phase shift. The FET driver burns 5 watts max to drive the 813 modulators to max power. Note: The 813's need about 50 volts POSITIVE  on their grids to allow for big audio peaks. This innovative FET audio driver could be used in place of most tube/xfmr drivers or backwards connected 8 ohm xfmr setups out there, if desired. Most any big or small plate modulated rig with a separate fil transformer for each mod tube will work.

There more stuff to talk about, but we'll save it for on-air.

73,

Tom, K1JJ


*Uploading is slow today, so will post pics as I can *

"GirlyMan"  4X1 pdm rig:  (has no BA transformers)

Shiznit, that's the biggest QRP rig I've ever seen.   ;D

Gorgeous.  -man, look at those coils; what with the price of copper these days, maybe a litle iron wouldn't hurt ;D

Can't wait to hear the beast on the air.

Those are not slop buckets on top of the rig.

Great googlie mooglie !!!  --Zappa

So Babar's mom was REALLY pee o'd when Babar unravelled all the TP rolls in the house....   "But Mom, I NEED them to wind coils for my PDM rig."

Well, in Tom's case he used sheet-rock mud buckets to deal with the slop buckets....I need to do a couple more to complete the new QTH this spring. We have a special one in the basement my son used early on before we had water. It is marked in bit letters "EPB"
Emergency Pooper Bucket. He only used it a couple times.
Single layer inductor makes the best pdm filter.

Hey Frank, I have a stack of those buckets of you need some....

I didn't even notice the inductors atop Tom's rig in the photo until reading Rick's post and looking again. Figured he just stacked some excess stuff up there. Now those are coils!
m

I need 2 or 3 with mud. SS pdm you can use PVC pipe. I'm working on my SS rig these days. The power supply is about done.

"Fabio"   Cuz it's pretty and smells so nice.    4X1 X 833C's

Side view of  PDM rig's RF deck (bottom)  and switch tube deck (top)  ...  cut-out normally covered with Plexiglas.  Plug-in coils, vacuum variables, chimneys on all tubes.

Can't wait to hear that thing on the air OM.  Perhaps the "lowest voice in America will show up 8)

LOOOOOOOK AT YOU TOM VU!!!!

PDM filter -  1,800 turns of #22 wire wound on THREE 5 gallon plastic pails.....   60 mh and 35 mh coils.....    Switching sidebands now down over -110db. This takes the place of the mod iron, so to speak.  Winding these was a perfect example of, "a mind is a terrible thing to waste."

you gonna be the master with the ghetto blaster.

Hi Tom,

Yikes !  Sheilding?  What's that  :D ;D  We don't need no STINKIN' shielding !   :o

But, seriously, if that rig is anything like my old 4-1000 PWM rig, the modulator will radiate energy like crazy (not to mention the RF amplifier, but that's another story).

There was MOOCHO high frequency RF energy radiated from the PWM filter (the input inductor and associated interconnecting wires were the biggest radiators).  There will also be considerable EM field energy in the vicinity of the PWM filter coils themselves.  I know, call me a worry wart, but I'd be rather concerned about the EM field radiation.  The RF energy radiation will be a TVI/RFI problem, but if you don't have any nearby neighbors, what the heck.  That EM field might be worth checking.

Otherwise, certainly has a "look", that's for sure!  ;)  Here's the PWM filter coil from my old vacuum tube PWM rig, and the associated filter for the equiv. solid state rig.

(http://www.classeradio.com/big_pdm_filter.jpg)(http://www.classeradio.com/air_wound_filter.jpg)

You guys will observe the solid state inductor is a tad easier to construct.
I agree with you Steve, but Tom Vu has no close neighbors. As far as near field I'm not crazy about being exposed to too much RF.
Chromerics makes some nice Shielded panels you can see through but not sure the low frequency attenuation is all that great.
Maybe he should consider some shielding once he gets things stable.
We like "ding lice is done" but wouldn't want Tom Vu to cook himself.
One of my "around to its" is to build and calibrate a field probe for the shack.

With that much stray RF in the shack, he wont need an "off air monitor". He'll be able to hear his own audio ok-fb ringing in his ears and dental fillings!! ;D ;D But Tommy has never been one for doing things in a small way ;D

Not in a small way indeed.

Sure is a good looking machine.
Love your construction standards, right down to the Rastafarian motif.

You'll be able to legitimately play in the Heavy Metal Rally with this beast, Tom, caw ! maw !

It warms my buzzardly heart -  I did miss you miscreants dearly.... :-)

OK on the unshielded cabinets, Steve.  Well, I've run unshielded stuff like this for years. I noticed that a large group of 95+ year old radio pioneer/broadcash buzzards died off in the 1990's. They all were overexposed to HF. I don't worry about HF with lifespans like that, esp considering the avg lifespans in the early 1900's.  HF PROLONGS life by killing off the flied lice.

Frank, I would like to hear more about the see thru panels you spoke of. Heck, I could even put aluminum screen over the Plexiglas if needed. I do plan to enclose the entire PDM rig into a Plexiglass display case. There will be no way to get across HV, even if you tried. I figure as an old buzzard, we all become forgetful and need failsafe barriers like that as we get lax.


Steve, I ran the PDM rig up to 1/2 power and had no acoustical ringing at all under normal voice modulation. Frank remembers our old 90's PDM rig's coils doing chin-ups with the bass notes... :-)  I then ran a PDM sideband suppression test: I put 500W into an antenna and listened on an antenna 300' away. The fundamental signal was overloading the receiver, while the sidebands were down almost in the noise. Maybe the house aluminum siding helps to shield the pdm switching noise, I dunno.  The filter attenuation with the series 113kc trap works quite well now.


Joe/BWO - your truck is running beautifully - I'm so glad I bought it from you. Still seems like new.


I picked up a few 4X1's so far. One may be close to new from Stu. That may go into Fabio with the new 833C's.


Paul, what is a RastaBraid?  Is that like a dreadlock? The rig does have a Jamaican look to it, I must admit man.
Yes, details, details. That's what it took to finally get that PDM rig working right. Bypassing, layout, suppressors, etc., it all adds up to stability.


Slab, you have a talent for taking pics of your 4X1's in action. I will get some later as things show some orange color.


Steve/QIX, I built up your new PDM kit generator. That is really a nice quality board with the feedthru holes. It had all the parts present except for one .018 cap. That's not a bad % for a kit, OM.  I'm hoping your new design will be more stable than the one I built using the point to point PCB from 2005.  We'll soon see once tested.


I want to post some pics and latest schematic of KLR's new FET cathode audio driver. I'm telling you, this board may become very popular once guys realize how simple it is to drive ANY modulator cathodes with a 5W fets. Neg feedback and absolute cleanliness.

Also want to post pics of the blown 813 X 813's. There's lots of guys who have built these up and the more pics the better to encourage building. That single 813 using 2500V will put out a fully modulated 500W carrier. The KLR FET audio driver board is the perfect match up for the triode-connected 813 modulators. It is the best sounding plate modulated rig I have built to date. Of course, GirlyMan will sound better with no mod iron to fuss with... :-)

I just hired my first employee - I train him every day, so will be flat out for a while. But hope to finish up GirlyMan once the PDM gen is built and the 4X1's arrive here.


DERB:  Real happy to see you're doing well and getting back on the air.  That BJB avatar is still the best one on the BB... :-)

Later dudes -

Tom, K1JJ   (Known on the east coast as "Ten-Large," caw mawn)

Hi Tom,

Very good !!  Although, when I was in broadcasting, I was exposed to RF energy - low frequency (broadcast band) pretty heavily, but NOT strong E/M  fields.  These E/M fields are what will be produced in the PWM filter inductor.  Those fields are not supposed to be good, and there have been regulations developed (many years ago) about exposure limits.  E/M fields are produced by anything with a choke or transformer carrying AC or varying voltages such as flyback transformers (old computer monitors running at very high frequencies), filters, etc.  These high energy transformers/chokes, running at 10s to 100s of killohertz will produce some fairly serious E/M radiation.

Ok on the board kit.  I'll check that part.  I don't do the kitting myself - someone else does it.  I'll check the master parts list and make sure it is there.  Each part on the list is checked off as it is put into the kit package.  With so many parts, it's necessary to have such a system!

Oh, one more thing - very important.  The PWM board you got from me is set up for a higher bandwidth system than you may have.  The solid state modulators have better high switching rate performance at small pulse widths (due to the lower impedance with respect to stray capacitance) than do tube modulators in the same service.  You will probably have to lower the switching rate from the stock 140+kHz to something below 100kHz.  You simply change the value of one resistor, the timing resistor (RT) - part of the SSM2166P PWM generator section of the circuit, to a lower value.  Pull down chip's the documentation form the TI site to see what to do.  It is a very simple change.

Talk later and Regards,

Steve

fo 10 - 10 - large 10 large my nappy headed soul brotha 10 large. I'm workin on my maw workin on my maw workin on my tuna trying to pull myself out of the mud so I wont be a muddy water slappa no mo. I'll have to dress up in my respect suit and pay my respects to the the one an only 10 large in charge when he lay his PDM maw down. I got teh southside covered brothaman and I'll see you in da ghetto real soon now.  8)

I just got down.  ::)

Yo BJB, my Papa-Large Rasta-Braided Bro!

I got ants in my pants and needs to dance.

Been gone so long I've got the laugh to keep from crying blues.

Ten-Large   (Good friend of FiftyCent)

Hi Tom,

 Very much a Master Builder your creations are Inspiring Tom Vu...Awesum....

I wouldn't worry too much. The maximum permissible exposure per the FECE is 56.26 mw/cm2 at 4 MHz. You only need to be a bit more than 2.5 feet from a dipole radiator (2.2 dBd gain) with 1000 watts input. Since all the conductors in the transmitter are very short at 4 MHz, I'm assuming their gain will be at least -10 dBd. This means you could run 10 kW and not exceed the radiation exposure limit.

What about us 100 KW FM dudes??????

Fell off of a ladder and broke my right arm two weeks ago. When they were taking X-rays in the hospital ER they tried to situate a lead-line robe over my nads. Told the nurse not to sweat it, I wuz DONE having kids. LOL.

MoFos set my arm the old western way. No bullet to bite on, no shots of firewater, just a dose of morphine and two docs pulled and twisted the arm until I could hear the bone ends grinding together...GOOD- Hold 'er there..." If I knew better I would have pre-medicated myself from the street pharmacy in downtown Boulder.

You're screwed.

How's it going there Big Country?

OK on the 4 mhz RF. I'm not worried about that.  But how about the EMF Steve/QIX mentioned above?  

There will be square waves and audio going through those coils at 113kc at the same current as the finals.  (The first coil will be 113 kc square waves and the next coil will be mostly audio.)

The coils will be about ten feet away from me when operating.     Each large coil is 10" diameter and has about 600 turns.

I plan to put a large Plexiglas in front of the coil area, but I wonder if I should add a wire screen for shielding too?

T

Tom,
Bit off topic, but I have been meaning to drop you a note and tell you I thought your letter to the editors of The Courant several months  back was well done.

73

Carl/ KPD

Thanks, Steve.

To think I sacrificed myself for "Don't fear the Reaper..."

Ola, 10-Large! Howzit hanging?

The exposure limit at 113 kHz is 100.00 mw/cm2. Even with 5000 watts into a full-sized dipole (imagine how big that would be) you only need to be 5 feet away to be below the limit.

Forget shielding. The field is magnetic. You would need eighth-inch or quarter-inch thick steel or mu-metal to do any real shielding.

Bill:





The limit at 100 MHz is 1.00 mw/cm2. If you are 190 feet away with 100 kW and a dipole, you are OK. Most FM arrays have more gain than that, but not at a negative 180 degree angle!

You guys ain't seen nuttin. The PDM rig Tom Vu built in '91 makes this look QRP.
Back then the power supply was too far away and he couldn't buy the parts he needed to make it hang in. Tim will remember the day of the Jacob's ladder modulating through the arc with a nice echo through the forest. I remember getting on the portable and telling him what he was doing. Then I had to ask. " how does the rig look making such a big arc across the feeders" He came back with " plate current is down a bit"

Tom,
Get yourself some metal window screen and put it against the Plexiglas it will work just fine and a heck of a lot cheaper.

Right, for magnetics, steel or mu-metal will do it !  I'm probably just being a bit paranoid.  After working at Digital in Electro-Magnetic Compliance for about a year (before going into development), I got sensitive to the whole thing  ;)  If you read the European regulations about this sort of thing, you'd think everyone who used an old-fashioned TV set or monitor was going to get cancer  ::)

OK on the E/M data, Big Country.  Looks like no problem.  But as Frank says, putting a steel screen against the big display Plexiglas might be a good idea anyway.


Carl - Tnx, OM.  You never know who's reading the newspaper... :-)   Yes, I saw enough careless people running their dogs on the ice - I had to say something about it. As you know, dogs have no idea that they can fall through and get trapped. It happens more in the late fall and early spring when the ice changing a lot...

Man, uploading speed has slowed to a crawl here in the last month or so. Comcast cable. Uploading a picture has become a real task. The video/movie downloaders are taking up all the bandwidth.... sigh    I also have trouble sending out an email with attachments > 100K.
The next commodity/energy shortage? = Internet Bandwidth.


T

Tom, haven't you heard ?

Comcast has taken its cue from the ARRL and has imposed a Bandplan on Bandwidth.

http://blog.wired.com/monkeybites/2007/09/comcast-custome.html
 (http://blog.wired.com/monkeybites/2007/09/comcast-custome.html)

Ah, yes....the BIG PDM rig of the early 90s. Wasn't that the one used frequently by Sgt. Anderson?   ;D

Looking forward to the return, T - maybe it'll get some of these signals offline and on the air.  The BJB has been on a few times, good sigs with 15 watts large.

i got the amp almost done - just needs a internal coax cable toobs put back in and some wiring checkout. I'm feeling a bit better today, I might go get at it.

"I'm as pretty as Fabio... and smell sweeter too, don't ya think?"

Yaz III

"And I'm smarter than Fabio too."
- Yaz


The Blown 813's under glass  -     (One 813 X 813's, plate modulated with new WA3KLR designed FET cathode audio driver)

Tom Vu sure love the plexi. Never known him to have rig with metal screen - makes his modulation xtal clear. (cum awn)