The AM Forum

Here are a few pictures of the just completed big rig I started several years ago.  Got distracted when I bought a Flex 5000A but now I finally finished it.  It's a pair of 4-400A's modulated by a pair of 3-500Z's.  Always wanted to try that combination and it seems to work pretty well.  I've had it on 160, 75, and 40 so far and will try and make the 20M Monday group with it soon.

A few more...RF deck, Modulator deck, and the final tubes close up

Very nice. Nothing like firebottles and windows.

Hi Chuck,

Well its nice to see the rig I worked you on last week!  As great as it looks, it sounds fantastic on the air as well.  Its nice to see pictures of your outstanding craftsmanship.  Some of the best looking HB gear ever.  You should write and article on it and send it to Ray out at ER.  

How about some pictures from behind the panels?   While I was typing you added some more. Fantastic layout and excellent attention to the details!

Looking forward to our next QSO when your using it.

Tnx OM!

Joe, W3GMS

Lots of shiny brass and lights; it must be a great radio!  :)

Gorgeous !

The epitome of fine AM.

A wonderful homage to the transmitters of yore.

Beats the heck out of modern stuff, IMO.

A good lesson in envy 101!

73DG

Good show OM!  It's all in the details..

You should be proud and I KNOW you're loud!  ;)

Clever use of the brass border accents.   Hours usage timer.
Symmetrical and well built.   Cool labels.   160 - 10 M - not an easy feat.  Neutralized?

Sounded FB on 160M, 75M and 40M recently.

I examined it on the workbench about 3 years ago.  Any pictures of under-the-chassis?


** Possibly the best-looking old buzzard style homebrew rig in North America....  ;D



T

Wow! That is a beautiful piece of work! Bet it sounds as good as it looks too!

Rob W1AEX

Beautiful workmanship - inside and out!  Thanks for sharing the photos. Schematics?

YIKES!
What can I say. I love symmetry and order. Your latest creation tops them all!
A lot more sparkle and pizzzazz than the "other" Big Rig.

And Chuck,
I have always felt that I should make a public apology to you for selling THE Big Rig I bought from you a few years back. It may have been re-sold or will be silent forever. I do not want to cause problems in the Ham community, but the amateur who bought it will probably never use it.
I felt that the way I was operating it, at reduced power, had changed the loading on the final and the modulator was never going to be happy and produce the TX audio it was capable of. Whenever I used it the reply about the audio was, "It just doesn't sound the same".
I am a Ham op who can say, " I used to own a T-368, or a BC1-H, or a Collins 20V, a McMartin BA-1K" The list goes on. Too much money available when I was single. Shameful.
But congrats on the beautiful TX, Chuck
Fred

BEAUTIFUL WORKMANSHIP!

How are you driving the modulators?

It is very beautiful, like a work of art!
yes please describe the modulator driver. What UTC iron is that?

Hi Folks,

Thanks for the kind comments on the new rig.  

The design is one that I came up with so no schematic is readily available but is pretty standard stuff.  Some of the variations from a "traditional" design are as follows:

1) The 4-400A grids are driven by a circuit that is "somewhat" passive.  I use a 2K 50W non inductive resistor directly from the grids to ground through a coupling capacitor.  The input matching circuit is a pi-net, the input tuning you see on the bottom of the final deck.  It is unconditionally stable on all bands and requires about 40 watts of drive, a good match for the Ranger driver.

2) Both tuning and loading vacuum variables are bolted directly to the chassis with Millen right angle drives to bring the controls to the front panel.  This provides the lowest parasitic return inductance from the output pi-net.  I've found that this approach results in a VERY stable amplifier.

3) Vacuum relays (Russian ones from Epay) are used to switch in the 160 M components with the front panel 160M switch. This switch successively switches in this order 1)Normal 80-10M  2)Add L-10uH)  3)Add C1-500 pF  4)Add only C2-1500pF  5)Add C1+C2  This allows a broad range of matching the output on 160.

4) The B+W 850A tank is modified to give the proper Q.  4 turns are removed and 40M tap is moved two turns for less inductance.  I removed it from the frame and mounted it higher above the chassis using a custom machined piece.  It is reversed so that the band switch can be seen through the front window and that knob in the middle of the window is the band switch connected through an insulated shaft coupling.  This provides a very short path to the tuning cap while having the 4-400A's right up front.  Gotta have that window!

5) The modulator uses a LS-33 line to speaker transformer reverse connected as the driver transformer.  The 500 ohm CT winding drives the grids and is just about perfect, generating the required P-P grid voltage with about 50 watts from the MOSFET Hi Fi amplifier.  Frequency response is limited only by the mod transformer which is from a 20V.  I had considered changing over to direct coupling from a MOSFET driver but this works so well I'm staying with it.  Really simple and RELIABLE!  Putting the 3-500Z's in front was easy and didn't require as much layout planning as the final.  Gotta have that window!

6) The control deck, the one with the custom brass rack handles on it, contains the variable fan, bias, screen, and the fixed 24V relay supplies. It also contains the Hammond 50H screen choke for self modulation.  This choke has an 18K 30 watt power resistor across it to provide optimized modulation of the 4-400A screens.  

7) The plate supply is common to the final and modulator and provides up to 3500 VDC.  Filtering is two 80 uF caps in parallel with a series 10 ohm 100 watt resistor from the full wave rectifier to keep p-p charging currents under control, something one should consider when using really big output caps.

8) T-R switching is accomplished with vacuum relays in the B+ lead to the modulator/final and in the 4-400A screen lead.  A 5K 100 watt resistor is switched across the heising choke to kill the inductive kick from it.  All these relays are correctly sequenced with diodes and timing caps across the relay coils.  No need for fancy logic here.

Well, that's about it off the top of my head but I'd be happy to answer any questions.  I've built quite a few of these rigs over my 50+ years in this hobby.  This is the brassiest one though!

Thanks again!

Chuck

 

Wow!  Nice job!  I hope this one's a keeper.

Eric

 
Can't wait to work you or at least hear it on the air. It looks melodious.  ;)

Wow, this is a superlative rig...

That is a work of art. Congratulations.

Steve

   Your rig was the topic of discussion last night on 14330, the "Monday Night 20M AM Group". There were just four of us on last night. We had hoped that rock crushing signal would appear...Maybe next Monday?

Jim
Wd5JKO

Wow, quite buzzardly!

Wondering how you made the brass escutcheons?

                      _-_-

Brass is class.

Very nice OM. I recall seeing the beginnings of that transmitter a few years ago. Congrats on finishing. Hope to hear you on the air with it soon.

Wonderful workmanship, OM. Absolutely Wunnerful (pronounce like Lawrence Welk). The craftsmanship I've seen is amazing. Can I post these on my facebook?

Philip

Thanks again for the comments!

To answer the questions on the brass, McMaster Carr is your friend.  I fabricated the brass "window dressing" from 3/8" X 1/8" brass bar stock.  I cut it to exact lengths to frame the windows and tapped the front panels for the 6-32 brass thumbscrews, also from McMaster Carr. Polish it up really good and your done.  The windows are ITO coated polycarbonate.  ITO (Indium Tin Oxide) is a transparent conductive coating used for shielding and capacitive touch screens.  Keeps the RF from the 4-400A's out of the shack, big difference on the FS meter with and without it.  The brass panel labels were engraved by a local place that does trophies and all sorts of engraved things like that. Less cost than I expected and worth it.  Better than the Dymo label maker.....

KOE: Sure, you can use the pics with attribution.

Yep...this rig will be a keeper...kinda wish I kept some of the other ones too.

I'll try and make the Monday 20M skeds but we've had a lot of thunderstorms in the area so all antennas are disconnected until this crappy wx goes away for a while.  Last night it got down to 38 degrees here.

Chuck

I just discovered McMaster-Carr. As they are in NE GA, I get next day service. Just ordered some little plastic pins to fix the pointers on the Valiant.

Holy Fire Bottles BatMan !

Chuck,
Even with s-9+15 static noise that beast sounded GREAT on 40 meters tonight (16 June 2014)!
I can't wait till I get to hear it on a less static enriched night.
Propogation was very good, but the static was using the props to full advntage, as well.

Like I was telling KC8ZUL (Gerry in Columbus) , "When I grow up to the big Iron I want to sound a lot like you" :-)

73 NICE work !

Your fine rig needs a name, to be known forevermore as your original creation. Those that forget or try to rename it be condemned to sidewinder Hadies.

I think "Brass or Brassy" has to be in there somewhere.
The rest is left as an exercise for the student. ; )

Kind of reminds me of a house " warming", so to speak, story.
Moving back from Pa., I bought my current house in '95 from a guy who was a proud cannon owner in a community of other cannon lovers around this smallish Maple Lake.  You can imagine the Rotary and 4th of July parties.

After about a year a couple of them mentioned that I " needed" a cannon.  Another year or so went by without me seriously taking the hint when one afternoon a truck and another car full of them showed up with a cannon which I was expected to buy, "at cost"

Well it's not a huge cannon by cannon standards, but a copy of a trunnion cannon mounted on a small field carriage hand crafted by my houses' former owner. I could not refuse.

Capiche?

 Brass Cannon!

http://brasscannonbrewing.com

I highly recommend it.

"The foam is on the bottom when you turn it upside down."

I had the pleasure of working Chuck on 40 meters while at my camp a week ago. It may have been one of his first such operations on 40 with the new rig? Sounded great on my R390A. A full body sound to say the least! Chuck never disappoints  ;D ;D ;D 

Hi Terry,

Hate to tell you this but I worked Chuck maybe 3 or 4 weeks ago on 40 with the new beast and its sounded great!  That was before any pictures were posted here on AMfone.  At that time I think he had not tried it on 20 meters so that was the next band to check it out on. 

The only issue at the time and I reported it to him was a little acoustical talk back from either the mod xmfr or the Heising choke.  He was going to look into that and come up with a solution.  While listing to it, it just had that slight ringing sound to it almost like a monitor speaker was on in the background.  It was very subtle for sure. 

Joe, GMS     

Hey Joe, glad you worked him. I heard other guest operators on his transmitter last week and I didn't hear anything on his audio that was out of place. Perhaps he fixed those things you listed or my ear doesn't hear what yours does?

Beautiful!  :o