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Baby Blue - Single 3-500Z self-contained Linear Amplifier




 
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Author Topic: Baby Blue - Single 3-500Z self-contained Linear Amplifier  (Read 1155 times)
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K1JJ
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"Let's go hiking in the woods, Tommy!" - Yaz


« on: August 28, 2020, 06:22:27 PM »

Well, here she is... Baby Blue.

Very compact, weighing in at about 110 pounds. The HV xfmr is big, but what I had to work with. The tube sub-chassis allows a direct connection to the blower for max air and efficiency. It is very quiet when Variac'd down. I could have used a few more square inches to fit everything in. The bifilar bypass caps had to be mounted on the aluminum strut...  Grin

One 3-500Z -  has a cathode input drive impedance of about 100 ohms. The tube was designed for two tubes = 50 ohms I guess. So in addition to an L/C tuning network I included a homemade  1:2 unun step up transformer. The swr is about 1.1: 1 on all bands once adjusted.  Gotta be flexible.

I painted the cabinet gloss black which really reflects the light as you can see. Black is a difficult color to hide imperfections so I had to be extra careful.

I put it thru the paces and cranked the HV up to 2200. I am able to get about 750 watts pep output, so a 125 to 150 watt carrier on AM is about right allowing for headroom.  I fired it up into a dummyload on 160-40M last night with full audio and was pleased. There are Variacs on the HV primary and blower.

When I tried to tune it up on 1885, it needed a bit more L or C in the tank.  It worked FB on 1895.  The little white coil was added to make it work down to 1870.  The roller inductor works FB on 40, 75 and 160M so far.

The bifilar choke is visible but the input tuning network and choke are shielded from the  tube and tank components.  The choke has a series of ferrite beads all the way down to the tube sub-chassis and also inside the box, so it is like a long inductor starting at the tube pins.  There is plenty of inductance at 160M. I measured about 700 ohms inductive reactance.

Baby Blue runs on 240 VAC.  The 240V AC relays are 24V coils and very robust. It has a step start.  That's a 35 uF  at 5.5KV filter cap.

I initially named it "Yaz" but renamed it to Baby Blue.  I may name my next rig, a 25 watt pissweaker, after Yaz.

In the pics showing the other rigs, Baby Blue does stand out.  It stands on rubber feet.  The tube uses a chimney and is viewable from the front panel.

This rig is intended as a driver for the big AM rigs with the Variac set to ~1000V and running in class C for greater driver efficiency.  It will double at 2200V as being a 125- 150 watt carrier linear driven by the hi-fi modified FT-1000D.   The FT-1000D alone was straining at the continuous carrier needed for the bigger AM rigs. It now takes only about 5 watts of carrier drive on AM. IE, the FT-1000D runs nice and cool now.

From left to right you can see  Hollywood, (813s X 813s)   Baby Blue, (3-500Z)    and Summer Breeze, (4D32 X 150 watt SS amp and Hammond transformer)   One pic shows the 4X1 AM rig on the extreme left.

It's nice to make some progress over time.

Tom, K1JJ


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Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #1 on: August 28, 2020, 06:24:46 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. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
K1JJ
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"Let's go hiking in the woods, Tommy!" - Yaz


« Reply #2 on: August 28, 2020, 06:26:27 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. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
K1JJ
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"Let's go hiking in the woods, Tommy!" - Yaz


« Reply #3 on: August 28, 2020, 06:28:19 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. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
K1JJ
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"Let's go hiking in the woods, Tommy!" - Yaz


« Reply #4 on: August 28, 2020, 06:30:04 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. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #5 on: August 28, 2020, 07:51:29 PM »

Baby blue....very compact....100lbs of amp in a 50 lb bag.....Welded box on that 3-500??

"its nice to make some progress over time"...You make plenty of progress...I get tired just following your projects.....Keep it up , you are doing great...   Steve
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Brrrr- it's cold in the shack! Fire up the BIG RIG


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« Reply #6 on: August 28, 2020, 07:52:17 PM »

Sorry, Tom, you said there's a tube in there, somewhere?  Wink

"It's All Over Now Baby Blue" - B. Dylan (and nicely covered by the Grateful Dead)


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K1JJ
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« Reply #7 on: August 28, 2020, 10:35:07 PM »

Yes, Steve, compact. As Old Buzzard George W1GAC used to say about his 813 rig RF deck, "I can carry it under my arm."   Not quite in this case.  Yes, that is a TIG welded alum sub-chassis. The weld flowed like solder. I taught myself to weld years ago and it is so much like soldering that it took no time at all to learn.  I started with a Lincoln AC electric box that made MIG and TIG easy in comparison. I think a DC electric box is the minimum to get decent welds though.

Bear, I almost forgot about those Baby Blue songs. I looked a bunch over on YouTube and this is the best BB video:
https://www.youtube.com/watch?v=UlIRUtJMA40

We'll have to make a recording to play when it's running, just like the Rico Suave rig days.

I added a handdrawn schematic for the record. I notice some of the homebrewers actually use these diagrams as a quick reference when getting stuck. Most rigs can use many of these same circuits. IE, the 4X1, 813 and 4D32 rigs are basically all the same design. And all my linears use the same basic diagram. It makes it easier to the point of building it without looking at the schematic except for the busy areas.

I am getting an itch to paint the other two rig panels Baby Blue too, but that is a lot of work.

T


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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. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #8 on: August 29, 2020, 12:19:39 PM »

Gorgeous stuff as usual Tom.    Grin

I've always thought your rig cosmetics are really eye catching, great color schemes
with good proportions of knobs vs. real estate, etc.

Nothing like matching meter sizes and types.  You sure have an eye for it.
A Properly blown 3-500 is so seldom seen these days. 
 
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« Reply #9 on: August 29, 2020, 02:05:31 PM »

With an air cooled filament choke as well! No wasted space in there.
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K1JJ
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« Reply #10 on: August 29, 2020, 08:57:33 PM »

Thanks, Rick -

I've always enjoyed different color schemes when painting HB rigs over the years. However, after seeing Baby Blue, my other rigs look kinda "albino" with the white panels and clear Plexiglas enclosures.  Actually the gloss black enclosure of BB is painted Plexi.  It slides off in 5 seconds for easy servicing, just like all the other rigs.

Back in 1972 I built what I called my "S" line.  It was five of those gray Bud shadow cabinets with panels. They were separate units consisting of an ssb/cw/AM transmitter, 11 tube receiver, pair of 813s linear, audio modulator, and accessories like CW keyer, etc.  The cool thing about the s-line was I painted the panels with silver paint and then used a translucent deep marina blue like a '67 GTO.  I rubbed out the GTO blue lacquer with 600 grit and rubbing compound until it shined like a mirror. The silver shined thru the blue like a mirror. What an effect.  Then I painted the beveled trim white around the panel and the cabinets black.  Real lookers.

I used the same translucent blue technique to later paint a Triumph 650 motorcycle tank and fenders and  a Volkswagen.

I've often wondered what a bright silver panel with a darker gray cabinet would look like.


Pat:  You are observant about the air cooled bifilar choke.  With 5V @ 14A going thru the choke, it does get warm when the blower is off. But the suction thru the choke actually cools it off. The blower runs so slowly that there is plenty of air intake even with the choke there.

I'll tell ya, the camera flash is really harsh on the rig viewing. In person the rig doesn't look as crowded and the tiny scuffs and other imperfections are not visible. Definitely some spatial distortion going on in the lens.  Camera lights take no prisoners.  In fact, in the Yaz picture, I noticed some dirt smudges on the staircase wall from years of rubbing against it. Years ago my elderly aunt used to "hold onto the wall" as she climbed the stairs. I just finished Windexing and cleaning the white walls and staircase... Grin   Maybe I need a tripod with external lighting and no flash.


T
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Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #11 on: August 30, 2020, 02:27:08 PM »

Tom,
not a photography expert here but here's what I have done in the past.  

Not sure what type of camera you're using but if a basic point and shoot, to control  camera flash glare, try a sheet of polarizing film or a translucent sheet over the flash.  Or a lazy man's fix is to partially cover the flash with a finger if it's just a brightness issue.  A little more trial and error is required with the finger more so than  the polarizing film or translucent sheet. The finger trick works good for close up shots in a lot of cases. There's no polarization but light dimming instead. Both techniques work well but mileage may vary depending on situation.  Polarization will reduce reflection intensity and would probably hide things the eye may not normally see like the wall smudges too.

For my Ebay sales which are usually small items that require close up shots I simply do the "finger over the flash" routine when using my Sony go anywhere pocket point and shoot. Especially if the item is of low reflection.  Quick and easy and I can usually  get a good shot in 2 or 3 attempts.  other shots I may use the "big guns".  Situation decides which camera I use such as something that is very reflective.  

A polarization example, I was selling a bunch of op-amp ICs I had bought years ago but never used. They went obsolete and I had no use for them so decided they would serve someone else better.  So I wanted to put them up on Ebay.  Problem was I could not get a good picture of the numbering and lettering on the top of the ICs. They were a little difficult to see in normal light with the naked eye but visible at the right angle and yet they were invisible to the camera.   I tried up close and far away with zoom and different angles. No matter what I tried I could not get a good shot of the top of the ICs with their part numbers. The numbers and letters were either washed out from brightness or to dim or plain invisible but yet, I could see them.  On a whim I used a polarizing filter on the camera lens of the Nikon. It still took some trial and error with filter position and flash angle to get a good shot but eventually captured the numbering and lettering.

The trusty old tripod in normal lighting without flash is a good way too.  One can setup lighting at varying points to get the best lighting with reduced reflection plus the camera can control the exposure time needed.  If a slow exposure the camera remains still and no blur from movement.

Imagine the old way with film and all the trial and error plus the time to process film to get that perfect shot.
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« Reply #12 on: August 30, 2020, 06:17:16 PM »

Very good info, Bob!

Iíll try the polarizing filter and finger tricks next.    

There are a lot of photo guys in ham radio, so maybe there will be more ideas.

Iím using a Fuji Film 3800 for what thatís worth.

Iíve noticed that using no flash at all, but a VERY steady camera (like a tripod) makes good photos for general viewing. The spots and smudges are not there and the detail is softer without the flash.

Maybe a video wud be a better idea to show the rig. The pics sure do make things look distorted and crammed in at timesÖ  For example the pictures showing the HV xfmr covered with white spots is not really there under normal light.

Does anyone have more suggestions for improving the pic quality of the ones I posted above?

T



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Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #13 on: August 30, 2020, 11:04:11 PM »

It's going to be the lighting, that's the solution. as mentioned, steady tripod, a polarizer though that may require more light. If you can pull the camera back and zoom in, it might get past some of the effects of the lens you complained about. More light will be needed for this.

A diffuse lighting from at least 2 maybe more sources since you have so much nook and cranny going on, and the lights placed so they look at the subject from the same side the camera does -or are in the same hemisphere, and offset enough to avoid reflections from shiny stuff. There's whole books on just that one paragraph LOL.
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« Reply #14 on: August 31, 2020, 08:06:01 AM »

I was looking at your schematic, and curious about one thing.  With the dc grounded grid, and the 25 ohms total resistance between the cathode/b- and ground, does this end up being a cathode biased amp, and dc wise, where does the grid sit relative to the cathode/filament ct without rf drive (ie whatís the standing dc bias)? Tube data and other works suggest zero bias is ok part of the time with the 3-500Z, but also that you can bias them on up into class C if desired, so curious where your amp ended up on the bias spectrum...

Ed
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« Reply #15 on: August 31, 2020, 10:11:15 AM »

The 50 ohm resistor lifts the power supply b- for metering plate current and grid current seperately.  Without it, you measure cathode current when you meter the filament center tap.  If you lift the grid and insert a meter directly then you run the risk of instability (although at the voltage level Tom is using, the 500Z is pretty darn stable).

The cathode is grounded at the same level as the grid, although you have to take account the resistance of the grid current meter.

For all intents and purposes, this is a 0 bias amp.


--Shane
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Tom, W8JI does a pretty complete write up on his website under metering (iirc) that will go into a lot more detail.
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« Reply #16 on: August 31, 2020, 10:52:43 AM »

The 50 ohm resistor lifts the power supply b- for metering plate current and grid current seperately.  Without it, you measure cathode current when you meter the filament center tap.  If you lift the grid and insert a meter directly then you run the risk of instability (although at the voltage level Tom is using, the 500Z is pretty darn stable).

The cathode is grounded at the same level as the grid, although you have to take account the resistance of the grid current meter.

For all intents and purposes, this is a 0 bias amp.

--Shane
KD6VXI

Tom, W8JI does a pretty complete write up on his website under metering (iirc) that will go into a lot more detail.


Hi Ed,

Shawn described what is going on with the metering and biasing quite well.

My plan is to have a dual purpose amplifier always in zero bias. I used direct copper straps from grid to chassis for stability and zero DC bias. One mode is to run at reduced voltage (~1000VDC) using the Variac to give me a low power class C carrier to drive the 4X1 and 813 class C AM rigs. (less than 50 watt carrier needed) With 1000V, there is no cathode/plate idle current and the amp in somewhere in class C -  there is no plate color either.

When I run the voltage up to 2200, I get about 100 mA plate current idle, which is about 220 watts of idle dissipation - a perfect level for a 500 watt tube to idle in class AB2 linear service to give me the 750W pep needed (125W carrier) for AM use (or ssb) with the FT-1000D driver.   So just by changing the HV Variac, I can go from a class C driver service to class AB2 linear service without the extra effort of changing bias. Also the B+/B- metering gives an accurate grid current reading as well as plate current.

The third meter is HV.  Notice I used the second 100 watt 450K metering resistor as double duty to also act as an additional power supply bleeder.

This overall design is probably the simplest  class C / class AB2 approach possible.   The 3-500Z tube was designed with a 100 ohm cathode drive input, so a pair is 50 ohms. Really FB tubes for the job.  They also make beautiful modulators and if the 3-1000A, the bigger cousin to the 3-500Z was more available, you can bet I'd use them in my 4X1 rig modulator rather than the 4-1000A in tetrode config.  But with regulated screen and grid voltages, the 4X1s are near perfect. (with NFB)   Just a lot more work to set up.

*BTW, did you notice I am using a 120V Variac to go 1/2 way across the 240VAC line?  The PS output range is about 1000VDC to 2200VDC compared to 0-2200V with a 240 Variac, but who has a 240 Variac that is small?  It is smaller cuz it handles just 1/2 the load. It's the Variac on the right side top on the front panel. Works FB for this app.  

T
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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. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #17 on: August 31, 2020, 07:28:01 PM »

I like the way you have arranged to run the amp way down to low voltages.

Isn't this like a plate modulated RF stage in the respect that the load impedance remains unchanged throughout the plate voltage swing?  - not regarding, or having to much be concerned with, biasing differences between this amp and the typical highly cut-off class C amp.
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« Reply #18 on: August 31, 2020, 09:32:01 PM »

Hi Pat,

I'm not sure about the impedance remaining the same, but it would probably do a good job running "class C AM linear" with the carrier creating the bias. The voltage at 1000 volts wud be a little low though.  At 1500V, Eimac says it approaches -45 dB 3rd order IMD which is possibly the cleanest tube amplifier out there.

I was on 75M tonight driving BabyBlue with the FT-1000D and the Tron said "don't touch anything".   His approval was the last step.  Here's a quick on-air recording of tonight where I am talking about Yaz going thru Rattlesnake avoidance class. There are rattlesnakes here and he was taught to smell, hear and see the danger and back off:


(I set the DSP low level transmit audio a little wider than normal:  bandwidth at +- 6KHz... it is usually at  +- 4.4 KHz)

https://youtu.be/mBMiRSMvWBU


I'm happy with the sound for now, though maybe the extreme highs are a little hot yet, I dunno. I'm now using a DBX DriveRack PA2 DSP processor with parametric EQ, Low Pass filter and limiter. Love how it is working.

T
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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. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
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« Reply #19 on: September 12, 2020, 01:19:25 AM »

Sure sounds fine! Clear and no noises from the shack or fans.
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