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Author Topic: The New 4D32 plate modulated project - "SummerBreeze"  (Read 24442 times)
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K1JJ
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« on: June 14, 2020, 01:46:12 AM »

As promised I am posting the beginning of my new 125 watt single 4D32 class C final -  plate modulated by a 150 watt Dayton class A/B solid state amplifier. The cool thing is I will be using a Hammond 1642SE 75 watt single ended audio output transformer. This is a super hi-fi transformer with 53H of inductance, 300 mA unbalanced current,  and weighs 28 pounds, costs $260.

Check it out: (Look at 1642SE specs)

https://www.hawkusa.com/sites/hawk-dev.ent.c-g.io/files/manufacture_group/HAMND/Series%201627-1642/spec/1627-1642.pdf

The Dayton 150 watt amplifier will drive the Hammond to plate modulate the 4D32 at about Valiant power, 125 watts output.

The new rig will be called "Summer Breeze" because it is a cool summertime rig with a small muffin fan. Probably the most efficient rig in it's class, besides a class D or E type rig.

It will serve a triple purpose.  One as a "little rig" to round out the plate modulated harem. Second, as an RF driver to provide a carrier for the bigger plate modulated 813 and 4-1000A rigs. Third, as a hi-fi exciter for my various homebrew linears.  The FT-1000D is the current driver but I am pushing it too hard. A single 4D32 in class C with the Variac moved low will work FB.

I included a temporary handwritten schematic of the whole rig below.  I was asked to suggest one for another ham on this forum building a 4D32 too.


I've been wanting to build a 100 watt class rig for some time now because there are times when I get on 75M in the late afternoon and it's foolish to run any of the big rigs when conditions are so good locally.

I also included some shots of Hollywood, the new 813 rig in it's resting position. I have it under Plexiglas for now until I modify a metal  enclosure.  But I am liking it under Plexi for viewing and really easy servicing in seconds.  I optimized the tank for 160M and 40M today. It worked FB except for the plate choke arcing on 40M. I had used enamel wire and rewound it using thin Teflon. Works like a champ now and Hollywood is band-agile. It is very stable for both RF and audio.

You will see the 17"X 22" X 4"  chassis for Summer Breeze as well as the front panel already mated to the chassis - in the staging area.  I'm just moving parts around for now and deciding just what to do.  I was up in the air about using 6LF6 sweep tubes as modulators, but decided to go the Hammond route.  My friend Jeff/ W2NBC has already built a rig like this using the 1642SE xfmr and says it's the cleanest and best sounding rig he ever built. This oughta be a fun project.  I will be using a 0-800 volt plate supply, separate screen voltage on a Variac and double tank loading caps to give me plenty of C2 load capacitance down on 160M.  One 4D32 is about 2400 ohms plate impedance, so there is a need for a lot of tank C.  I am using a roller inductor for the coil with turns counter. I shud be able to switch bands in seconds with presets.

More to come as I start drillling and blasting.

Tom, K1JJ


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K1JJ
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« Reply #1 on: June 14, 2020, 01:52:06 AM »

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K1JJ
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« Reply #2 on: June 14, 2020, 01:53:11 AM »

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K1JJ
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« Reply #3 on: June 14, 2020, 01:53:44 AM »

That's it for now...


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« Reply #4 on: June 14, 2020, 06:53:45 AM »

Why muck around with 4D32s when one can step up to the latest in vacuum tube technology?  As they say at the dogsled races, "Unless you're the lead dog, the view never changes."

http://www.tubecollectors.org/archives/606.pdf

73 de Norm W1ITT
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« Reply #5 on: June 14, 2020, 10:19:03 AM »

I had a bad case of those.  Cured by sending them back...

73DG
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« Reply #6 on: June 14, 2020, 10:21:49 AM »

I included a temporary handwritten schematic of the whole rig below.  I was asked to suggest one for another ham on this forum building a 4D32 too.

Tom, K1JJ

Check your bias rectifiers...small error there...

Curious on PTT.  Looks like you’re switching the screen and HV into a lower voltage using a step start?



Ed
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« Reply #7 on: June 14, 2020, 11:38:57 AM »

Slimatron?

Why muck around with 4D32s when one can step up to the latest in vacuum tube technology?  As they say at the dogsled races, "Unless you're the lead dog, the view never changes."

http://www.tubecollectors.org/archives/606.pdf

73 de Norm W1ITT
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K1JJ
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« Reply #8 on: June 14, 2020, 12:42:53 PM »

I included a temporary handwritten schematic of the whole rig below.  I was asked to suggest one for another ham on this forum building a 4D32 too.

Tom, K1JJ

Check your bias rectifiers...small error there...

Curious on PTT.  Looks like you’re switching the screen and HV into a lower voltage using a step start?


Ed


Hi Ed,

Thanks for the heads up on the bias supply rectifier error. Yes, the diodes should look like the screen supply, except with the diodes backwards. I will replace the schematic later today.

The PTT step start brings (keys)  the HV up slowly at the same time as the screen supply.   The fixed protective bias is always on with the initial switch.  I am using this system with the 813 rig now and works FB.  I also use a "snubber" across the mod sec winding that shorts a 3K power resistor to kill any unkey magnetic collapse. It uses a series resistor with a vac relay that is normally on when in receive and lifts when in transmit. I did not need a sequencer with the 813 rig except with for the HV step start.. No arcing.

I learned that the screen and grid supplies need a good bleeder equal to the operating current to maintain stability. The grid bias can charge up the filter cap and make the rig impossible to drive when using smaller bleeders.   Regulated supplies wud help, but unnecessary with class C.

Another thing I found yesterday with the 813 rig fine tuning is that the loading and tank tuning is important to get the very best audio waveform above 5KHz or so.  As the modulator struggles to maintain good form at 7, 8, 9, 10+ KHz, the modulator load (the RF final) has to be near perfect or the fragile modulator causes ripples or slanting at the extreme highs. I see the IMD and harmonic distortion increase too.  No problem below 5KHz and tuning can be more general. The intra-turn and general loss of mod iron at the extreme highs makes the tubes need more current to maintain a good waveform too.  Bottom line is I have precise settings for C2, L1 and C1 on the various bands thats gives me the very best extreme high frequency waveform as possible and at the same time good power output and efficiency.  It takes some juggling to find these sweet spots, but when done, the high end looks really FB when limited to 6.5 KHz and there is plenty of clean bandwidth headroom above.

Norm:  That old buzzard tube looks like the ancestor of a 750TL. I ran a pair back in the 70's.  A dead, dumb triode with an amplification factor of 12, but oh what a look! Like a movie star.  I had six at one time, but one by one the filaments went bad due to the manufacturing shortage of tungsten during WWII.

T


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« Reply #9 on: June 14, 2020, 07:10:35 PM »

Updated schematic for 4D32 rig:


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« Reply #10 on: June 14, 2020, 07:30:54 PM »

Looking at the new schematic there’s one other thing that caught my attention— the cathode to filament voltage. Specs say they should be connected, or less than 100v apart. Since it’s only the one filament tying them together is simple enough...

Ed
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K1JJ
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« Reply #11 on: June 14, 2020, 09:39:03 PM »

Looking at the new schematic there’s one other thing that caught my attention— the cathode to filament voltage. Specs say they should be connected, or less than 100v apart. Since it’s only the one filament tying them together is simple enough...

Ed


Yep another good catch, Ed.   I will connect the fil xfmr CT to the cathode. That will keep the voltage differential to minimum.

BTW, I just noticed that the 500 pF plate coupling cap needs to be moved to the right to let the DC pass to the tube. Corrected and I will post a new schematic soon.

I don't mind making mistakes on paper at all... :-)

T
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There's nothing like an old dog.
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« Reply #12 on: June 17, 2020, 04:10:58 PM »

"SummerBreeze" (named by Jeff, W2NBC) has been Brillo-padded down and is ready for painting the front panel. The front panel will get a few coats of paint to fill in any scratches.  Except for terminal strip placements, all of the drilling and blasting is finished.  Time to paint and then start mounting parts.

You will see the transformer iron painted in gloss black, ready to mount on the chassis.  The 4D32 tube sits right in the front next to the big, rectangular viewing window.  The 3" hole on the bottom left is for the turns counter controlling the roller inductor.  There is a second loading cap mounted underneath the 4" chassis giving a total of 4,000 pF, good for 160M and the low 2400 ohm 4D32 plate impedance, with a Q=20.

I think it will weigh close to 80 pounds when complete...  just about like a Valiant.    Very strong custom-welded chassis and side supports. The panel is made from a very hard aluminum. All came from the scrap yard for cheap - bought by the pound.   The extra holes in the chassis will be filled in with screws - and were free... :-)

Same power class at 125 watts carrier out.  All power supplies onboard. The Hammond audio transfomer alone weighs 28 pounds.  The 800 volt HV xfmr is about 20 pounds. Six beer-can-sized filter caps. Three Variacs and two very heavy loading caps all start to add up.  She's gonna be a beautiful lower powered standalone rig /carrier driver/ linear exciter capable of a wide power range using the Variac HV supply. The single 4D32 tube will make a great final. I'm happy with my overall decision.   The 4D32 is my third favorite tube for AM work - with the 4-1000A first and the 813 second.

T


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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.
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« Reply #13 on: June 17, 2020, 04:12:24 PM »

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Yaz had a little mishap running into a rusty hay rake at night.  He is healing from a cut on his leg that he kept licking.  One more day wearing the Elizabethan collar.


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There's nothing like an old dog.
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« Reply #14 on: June 17, 2020, 06:55:37 PM »




I thought he was working moon bounce. The coyotes around here try it without the collar.

klc
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K1JJ
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« Reply #15 on: June 17, 2020, 07:14:04 PM »


I thought he was working moon bounce. The coyotes around here try it without the collar.

klc


Heheheh… good one!   And he's looking up at the moon too.

I got SummerBreeze some paint and he's out in the sun baking it on.


I may fill the chassis and panel with parts later tonight if it dries well. It's very dry today.


Nothing like a rig filled with parts but not wired yet. It will never look better than that. Something like meeting a blind date in a dim bar.

T


BTW, I was going to paint the panel Baby Blue, but may save that one for the next Pissweaker rig.


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There's nothing like an old dog.
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« Reply #16 on: June 17, 2020, 08:43:28 PM »

Always love to follow your projects!
Full metering!

Elizabethan collar LOL


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« Reply #17 on: June 18, 2020, 02:50:34 PM »

Tom,
Nice looking chassis!  Did you do the bending and welding?  Nice looking welds. TIG?
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« Reply #18 on: June 18, 2020, 07:24:34 PM »

Tom,
Nice looking chassis!  Did you do the bending and welding?  Nice looking welds. TIG?


TNX, Bob.   I picked up the chassis and sheet aluminum at the scrapyard for $1 per pound. The chassis was already built. I'll cover up the extra holes soon.


Just like a Heathkit, the new rig went together quickly. Now it's time for wiring which always takes a lot of time....


I'm missing the Hammond audio transformer. I took some pics with the tube fan mounted and without to clear the view. It will be a fun 125 watt rig to run.
There is another C2 2000pF loading cap under the chassis in parallel with the topside one. I'll take some under-skirt shots once it is wired up.

Notice I mounted most of the heavy iron towards the middle of the chassis to make it easier to carry.  The RF stuff HAD to be in the front for access and tube viewing.

T


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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.
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« Reply #19 on: June 18, 2020, 07:26:27 PM »

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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.
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« Reply #20 on: June 18, 2020, 07:27:50 PM »

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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.
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« Reply #21 on: June 18, 2020, 07:28:49 PM »

Notice the cooling fan above the tube. It is on a Variac to be slow and quiet. This pushes air DOWN around the tube very well. The socket is sub-mounted for some base seal circulation too.


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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.
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« Reply #22 on: June 18, 2020, 07:38:05 PM »

Tom,

Which direction does the fan move the air over the PA tube?
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K1JJ
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« Reply #23 on: June 18, 2020, 07:51:21 PM »

Tom,

I realize it is against the grain cuz heat rises, but I experimented a lot with muffin fan placement when I had the 4D32 dual quads. I wanted to cool four tubes in a square with two fans. Without a doubt, this works best: The air is focused down from directly above and comes down to the base, the air then bounces off the bottom and spreads out evenly as it moves to the edges of the chassis. It requires a ventilated cabinet.  Air hits the plate cap, all glass and even some bottom seal area if the tube has a mounting gap.  I usually test it by leaving the filaments on for a long period and increasing the airflow with the Variac until I can touch the glass without getting burned. You can feel the tube all around its 360 degree circumference and see if there are any blind spots. But one tube is very easy to service with one fan.   There is excellent air control when it is forced directly down vs: from the side.  

Of course, a pressurized chimney airflow from the bottom is best with a fan that can handle back pressure.  But I wanted this to be very simple since a 4D32 needs no forced air anyway.  

T
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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.
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« Reply #24 on: June 18, 2020, 08:11:31 PM »

Better closeups:

I have 3/16" Plexiglas in there now... I usually use 1/8" glass.   I think the glass is clearer.

The L - C  input network is mounted under the chassis, as well as the HV Variac, the fil xfmr, screen and grid circuitry and a few other things to hide the wires.

T


* DSCF0006.JPG (335.65 KB, 1280x960 - viewed 490 times.)

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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.
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