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Another 813 Build




 
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Author Topic: Another 813 Build  (Read 15090 times)
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W1RKW
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« Reply #75 on: March 17, 2019, 05:04:41 PM »

I have an enclosed rack that I acquired from Joe/WB1AIU which is the home of GORT.  The rack is 4.5ft tall and is 24 inches deep. I mounted it on heavy duty wheels. Between the rack and the hardware installed in it, it's about 250lbs. It has 19" rails both in the front and in the rear.  I took advantage of of the rear rails by installing perforated angle iron between the front and rear to be used as sliders for the 4 chassis support sections of the transmitter. There are 2 chassis's with transformers and there is no way that the front panel of each chassis will support itself let alone trying to install and remove those chassis's by removing and installing the mounting screws. That would take to people.   The rails provide support and unstress the front panel and I  am able to remove/install each chassis by myself.  
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Bob
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Home of GORT. A buddy of mine named the 813 rig GORT.
His fear was when I turned it on for the first time life on earth would come to a stand still.
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« Reply #76 on: March 18, 2019, 08:03:21 AM »


I have a question for the group related to the screen clamper, etc.  

**Update:  Never mind - question answered offline.

T

Tom, after thinking about your question and because I did not arrive at any valid hypothesis on my own, I refrained from commenting prematurely.  But I (and possibly others) would  like to hear what you learned offline about the behavior of the screen grid voltage and current when using the combination of fixed and grid-leak bias as the grid current changes.  (I was out of town for a few days, hence the delay in my comment.)

Thanks in advance for taking the time to elaborate!
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Rick / W8KHK  ex WB2HKX, WB4GNR
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« Reply #77 on: March 18, 2019, 08:37:17 PM »

Hi Rick,

Actually I wasn't really satisfied with the answer I received and didn't want to waste any more time on it.  I decided the next time I fire up the 4X1 rig I will see for myself exactly how the screen current responds to grid drive as the grid leak bias increases.  It eventually settles at 280 mA with full grid drive and with the Variac-driven screen voltage adjusted right, but the path it takes to get there, I don't remember... :-)

T
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #78 on: March 18, 2019, 09:31:56 PM »

Thanks for the explanation, Tom. 
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Rick / W8KHK  ex WB2HKX, WB4GNR
w9jsw
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« Reply #79 on: June 16, 2019, 07:58:39 AM »

Finally! I am in possession of my rack. Is an old Motorola comm rack. Built very well. Has some nice stainless louvers on the bottom that will really help air flow - and look super. Needs a good cleaning.

I have stripped off the sides and the front (now back) door. I positioned the rack bars so that the transmitter will have the faceplates flush with the now front line of the rack giving me a whopping 17x17in space to mount the mod and RF chassis. I had bought a 17x17 one but now will trade it in on a 17x15 one. Glad I was not premature on cutting on the chassis. This will be a bit tighter but will give me room for cables on the back of the chassis and still be able to close the door.

Putting in a 3/4in plywood floor and casters to allow easy movement. First task is to position all of the iron for the PS components on the wood floor. I may have to do a double decker for some parts like the caps. Gates had all of the iron on the floor of the rack. Having the sides off will make this build much easier. I am using 5/16 bolts and t-nuts to make the iron solidly attached to the unit. I have 175lbs of iron to mount. Casters can handle 600lbs of weight. I am thinking I will be in the 400lb ballpark when finished. Heavy metal baby!

I will then start on the power control chassis. Then modulator and last the RF deck on the top. Included the schematic for anyone following along.


* Rack.JPG (1159.29 KB, 2448x3264 - viewed 97 times.)
* 813 Transmitter.pdf (185.69 KB - downloaded 38 times.)
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w4bfs
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« Reply #80 on: June 16, 2019, 01:09:23 PM »

ain't nuthin like a big homebrrrrrew project ! Cheesy Cheesy   like the new avatar as well
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Beefus

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w9jsw
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« Reply #81 on: June 16, 2019, 01:42:43 PM »

Was on the shore of Lake Erie with a microbrew in my hand. One of my better days.
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w9jsw
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« Reply #82 on: June 16, 2019, 02:54:32 PM »

A big homebrew is a bit like this game

https://en.m.wikipedia.org/wiki/Three-dimensional_chess

Just about popped a nut just moving them into position. Definitely going double decker!

Think I will put a layer of aluminum between the wood and the iron. Better ground for all the iron and no visible combustibles. Overthinking this?

John


* trans1.JPG (577.64 KB, 3264x2448 - viewed 104 times.)

* trans2.JPG (590.13 KB, 3264x2448 - viewed 81 times.)
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KL7OF
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« Reply #83 on: June 16, 2019, 05:25:49 PM »

Yes overthinking...Old Iron is actually better mounted on wood..Frames not at ground potential....IMHO
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w8khk
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« Reply #84 on: June 16, 2019, 05:37:28 PM »

Yes overthinking...Old Iron is actually better mounted on wood..Frames not at ground potential....IMHO

Yup, that is the way I do it too.  No need to bolt 'em down, either.  Just place them with reasonable clearance, and they will stay put, even with the rack on casters.

In my 250TH rig, I used an HP 5KW isolation transformer.  it had a slight hum, even on the wood, so i placed it upon a one-inch thick slab of styrofoam, quiet as can be now. 

By the way, when I was about five, my dad was fixing a radio for me.  It needed a new filter cap.  But when I asked him why it hums, he just said "because it doesn't know the words."
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Rick / W8KHK  ex WB2HKX, WB4GNR
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« Reply #85 on: June 16, 2019, 07:15:21 PM »

Wood is good! 3/4" is a bit thin for 'no flexing' with that heavy stuff there. Probably 2x6 or 2x10 planking is more than enough to make a great floor and will just fit side to side, depending on the rack.

Personally I like to secure the iron in place and do not understand why people like to have it loose, just set in place. To ground or not to ground? depends on the parts and safety concerns if someone else ever has to work on it.

Planks let you run 1.5" x 1/4" or 3/8" lag bolts into them to fix the iron in place yet be able to remove it easily with a 7/16" socket if wanted. Fender washers under the bolt heads keep from scratching the transformer frames.

A piece of angle iron across the planks at each end hold the 'crack' together great. I did it a little different, running transformer bolts into the angle too, but that floor is solid due to the angle iron and nothing is going to move.

Overkill? maybe, but we should each do what makes each of us happy!

Just thinking long term because this kind of equipment you are building could last 50-100 years if done right.

p.s. don't use water-resistant/pressure treated wood. The chemicals can slowly corrode metals.


* rackfloor.JPG (204.18 KB, 1074x603 - viewed 100 times.)

* rackfloor2.JPG (150.12 KB, 1132x339 - viewed 99 times.)
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« Reply #86 on: June 16, 2019, 10:28:13 PM »

Yes overthinking...Old Iron is actually better mounted on wood..Frames not at ground potential....IMHO

I was called nuts for stating frames should be isolated.

--Shane
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K1JJ
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« Reply #87 on: June 17, 2019, 12:40:03 AM »

Hola John -

After a brief interlude, you are back.  I also like the new mellow avatar.  You look like a salty dog on the sea..  Wink

Paint the rack a nice IBM computer/ blue like below..

As for big iron mounted on wood, I have always done this with mod xfmr, chokes, Heising caps, HV power transformers, etc.  The practice simply keeps an old transformer from risking it's frame to wire insulation rating.

The only downside I see is a safety risk in case of the slim chance that one of the internal wire turns touches the frame/case after a blow out and puts the frame and case at full potential. (Or the wire to frame insulation simply fails)  I've had a Heising cap, 5 KV @ 2 uFd once internally short to the case and make the case hot for HV.

Any thoughts on this?


BTW, how do you get "Two shots of whiskey" from JSW?   Is that AFTER drinking a whole bottle?

T


* DSCF0007.JPG (337.31 KB, 960x1280 - viewed 87 times.)
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
w9jsw
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« Reply #88 on: June 17, 2019, 06:35:51 AM »

Whisky 9er Juliet Sierra Whisky - sound it out.

Having a hot frame on the iron worries me. I think I would want it to blow the fuses if a short developed. Look at the other side - you have a transmitter that continues to operate but you now have a risk of fire if it starts to arc due to anything bridging the frame to ground - perhaps a mouse or something. Or you fiddling where you should not and touch a frame that you THOUGHT should not be live. I think I want it grounded. Convince me otherwise...

John
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w9jsw
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« Reply #89 on: June 17, 2019, 12:29:14 PM »

Or is the idea that if you float the frame on a 60 year old transformer it will make it less likely that it will short.
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K1JJ
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« Reply #90 on: June 17, 2019, 02:59:59 PM »

Yes, that's the idea.

It's safer to ground the frame so that if the insulation fails, the HV fusing system opens and kills the HV source.

Though, there are lots of exposed HV points in the rig and if the HV power is on we have no business touching anything inside anyway.  IE, whether we touch a hot transformer case or the HV diode stack, we get zapped.

I personally prefer to float the iron on wood or Plexiglas and never touch anything inside the cabinet when the HV power is on.  Always act like the transformer case is hot. We could make up a Plexiglas enclosure to put over it, I suppose.

"Whisky 9er Juliet Sierra Whisky - sound it out."  I see two whiskeys, but how does 9er Juliet fit in?


T
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #91 on: June 17, 2019, 05:14:23 PM »

If you really wanted to be safe from a shorted frame, tie a resistor to the frame of the isolated xformer / choke and use ohms law to drop it to 120 volts (or 24, depending on the trip voltage) and hit a shunt trip breaker.

That will keep the breaker from staying live under any circumstance darn near.....  Even if you lost ground connection to the chassis somewhere/how.

This is how electric is cut during a fire or other event in commercial and industrial electric.

--Shane
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« Reply #92 on: June 18, 2019, 03:34:43 AM »

If wood is used for a floor, then a heavy jumper can ground the transformer frame to the chassis or the protection scheme can be used. There are always options.
The pictures were only to show what I thought was a great way to make a real strong floor in a rack at almost no cost.

In my 1950's 4-1000 homebrew rig, everything is grounded to the cabinet but the mod transformer, because that item is very ratty and from the 1940s. The rest of the stuff was new at the time. The original builder did not ground the mod iron because he was sometimes running 5KV in there. When I put the thing back together I rewired the HV supplies to make only 3300V.

When designing and building something new like in this topic, there's a perfect opportunity to put the low voltage and control circuits well away from the high voltage parts in case some work has to be done.
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w9jsw
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« Reply #93 on: June 18, 2019, 06:57:53 AM »

ok, got it.

HV gets assembled this weekend.

What do you all use for a HV probe? I am thinking of buying the BK 28A one.

https://www.amazon.com/Precision-PR-28A-Voltage-Attenuation/dp/B004PA02Q8

John

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« Reply #94 on: June 19, 2019, 01:04:53 AM »

That one would be great for ham radio work, just use a lower scale on the meter. I see it has a ground clip. That's the safety feature as well as the tapped multiplier return.

No matter what kind storebought or home made, I never like to hold them while measuring, but I'm shy after being hit by a color TV set because of a faulty probe.

Some of the TV set types like that 40KV unit on Amazon used to come with a slip-on spring hook that let it hang in place without being held.
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« Reply #95 on: June 19, 2019, 01:26:21 PM »

ok, got it.

HV gets assembled this weekend.

What do you all use for a HV probe? I am thinking of buying the BK 28A one.

https://www.amazon.com/Precision-PR-28A-Voltage-Attenuation/dp/B004PA02Q8

John


I have that same probe and found it indispensable when probing HV circuits.

I used it a lot when checking voltages on the HV circuits in my 813 based 175 watt Screen Modulated, 3-band, homebrew transmitter, which had an HV B+ of 2,200 Volts.

 
Your build would make for a great article for Electric Radio magazine.  Cool


Phil - AC0OB

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« Reply #96 on: July 04, 2019, 04:06:54 PM »

Progress...

Have the front panel laid out to mount the power switch, breakers, HV Meter and the honk'in powerstat. Time to make some holes. Power switch is one of those NC/NO ones that works in conjunction with a 3PDT relay to have the power shut down completely if there is a mains glitch. Will also have my back door interlock in the circuit so that if the door gets opened, it all shuts down.

All the iron mounted. Tight.

Working out where to place the big caps and the relays. I think the caps will mount on a side shelf strapped to the side of the rack. A similar shelf on the opposing side to hold the 3 relays. I think that will work. 

Do the magnetics generate much heat? Mod trans and mod reactor are pretty close. Can move them an inch or so if necessary. Those are the two in the back - L3 and the white tag one.

Glad I have 6 feet of rack to work with. The plan shows it all fitting with a 3U space left over. Thinking about a 3 fan spacer and running the fans at 1/2 voltage. The bottom of the rack has stainless louvers so that should create some good airflow and hopefully not be too loud.

John



* HV-Front.JPG (125.81 KB, 568x757 - viewed 77 times.)

* HV-Powerstat.JPG (103.88 KB, 531x708 - viewed 94 times.)
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« Reply #97 on: July 06, 2019, 06:30:40 PM »

Not to pick, but laminations are facing same way on power and audio iron -but it's not a preamp being built after all!

Looks like it will all be grounded, so close-in but it's fairly new iron. Doubt you will really have any shorting or heat issues. I think it's great! Love generous power supplies.

Nice big Variac as well. Have a shot of Red Cat to celebrate!


* The cat will get ya.jpg (42.2 KB, 468x900 - viewed 43 times.)
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« Reply #98 on: July 07, 2019, 06:46:06 AM »

Still fiddling with the layout.  Roll Eyes

Changed orientation of the mod trans and mod reactor to make more floor space. BTW, floor is 2 sheets of 3/4 in plywood. Plenty stout and give me an ungrounded mounting platform. Also bought some insulated terminal boots to allow me to cover up all of the connections to insure no possible arcing in the future. White wire is 20kv rated, red wire is 30kv rated. Diode string is mounted on polycarbonate with a insulating sheet below. White posts are for the HV fuse. All caps will be secured once I finalize the plan.

Option 1 fits all of the caps on the floor, but I lose one of the large caps so I go from 64uf to 32uf on the PS caps. 32uf is still 4X what the Gates had which was 8uF.

Option 2 maintains the 64uf of PS caps but I then have to place the reactor caps up high on the side of the frame. Longer leads on the caps which I generally do not like.

Which would you do and why?

John


* Option 1.JPG (629.58 KB, 3264x2448 - viewed 51 times.)

* Option 2.JPG (334.42 KB, 1836x2448 - viewed 66 times.)
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K8DI
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« Reply #99 on: July 07, 2019, 08:17:58 AM »

Being pessimistic, but what about serviceability? If you mount the iron and caps like that, how do you probe anything, let alone change taps or remove one of the transformers, without taking it all apart?

Ed
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Ed, K8DI, warming the air with RF, and working on lighting the shack with thoriated tungsten and mercury vapor...
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