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.

Very nice. Nothing like firebottles and windows.

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

A wonderful homage to the transmitters of yore.

Beats the heck out of modern stuff, IMO.

A good lesson in envy 101!

73DG

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....  



T

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

BEAUTIFUL WORKMANSHIP!

How are you driving the modulators?

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.

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

 

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

That is a work of art. Congratulations.

Steve

Wow, quite buzzardly!

Wondering how you made the brass escutcheons?

                      _-_-

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

Philip

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.