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starting work on the amp




 
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Rick & "Roosevelt"


« Reply #25 on: May 11, 2016, 01:32:20 PM »

RAT STASH 3000
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« Reply #26 on: May 15, 2016, 07:43:35 PM »


RAT 3000

Hmmm..
Not sure how to work the powerstat in, but it's just a handwheel. Haha later on, maybe I'll drop a note to Superior. I got a nice reply after telling them how pleased I was that the 60's Stabiline here was performing flawlessly without regard to age.

Now RAT 3000 I like.. For one, it does not use the peak output as a brag, like the cheap stereos of the 1960's. it'll have to wait until this is built and tested tho'  Wink


Today, I quote Dr Smith: "The PAIN the PAIN!!" I lifted nothing but spent a lot of time on the floor and close to the ground making and fitting and unfitting and remaking and bolting brackets and bolts and warshers and all that kind of stuff. What a wreck I made of myself. Without my young apprentice, this would not be possible. He is like the son I never had, but if I had a family, would want. My luck in that regard however would stick me instead with the son that that trashes the car and won't get a job. So this is good.

The Powerstat was moved back an inch to a perfect fit so the handwheel is 1/4" from the front panel. Just enough rheum for the fine 0-100 round scale to fit behind the handwheel.

Now this is not really an heroic handwheel, or is it? Three spokes and a hub does not a wheel make. What is this human interface device called, properly?

What I would prefer, but is not to be found, is a big lever that moved up and down on a radiused panel mounted escutcheon. These were sometimes used with Ward-Leonard rheostats for stage lighting controls. The lever pulls a chain like a bicycle chain, this is transmitted by pulleys to a gear on the shaft of the rheostat, so why not a powerstat?
(black and white images)

However, I'd like a longer scale/bigger radius on the lever than shown in the panel if possible. Those scales probably are about 8" long, and the lever tips may be traveling 18".

Point is that it's not lighting which would use a coarse positioning, but a Powerstat, made for greater accuracy. The scale should be 0-100 and be able to be set easily to within 2 points or so. Those that have operated old Ward-Leonard rheostats know that the levers could be hard to position precisely, slow to push. In high school we had a stage lighting console with similar resistive devices but the individual escutcheon was about 12" long, low to the panel with a large radius, with the handles protruding about 6" from that. Real easy to move.

Hey it's art.

OK now having wiped away the drool from looking at those banks of controls, here are the pics of the progress today.








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« Reply #27 on: May 15, 2016, 08:27:16 PM »

To improve the strength of the front mount, two holes were drilled in the supporting panel and instead of rackmount screws and nuts, grade 5 1/4" bolts were used, with washers on each side and also the nice 'nylon insert' nuts. These can be used instead of lockwashers. They may not stay as tight but they will not vibrate off or work loose to where the nut falls off and are popular on drive shafts. In this job it probably does not matter which is used, nut and lockwasher - vs - nylock nut. It only matters the strength of the fastener.

Mounting the back of the Powerstat was an interesting exercise and also painful for arthritis and back issues to kneel behind the rack and reach in to do this fitting up the pieces.

A thicker angle iron could have been used such as the side supports at the rear, but it was as well to use the flat metal because all the holes lined up well and 3/8" hardware was used between the X braces and the angles. the angles were fastened to the rack by 1/4" hardware, and believe it or not the holes did line up nicely.

Where a bolt head or nut  was small compared to the hole (some oblong holes) in the angle, a large fender washer was used to provide a flat surface. This is important because it prevents the edge of a nut or bolt head from going down into the end of an oblong hole, which would cockeye the bolt, or the tension on the bolt, when tightened.

The front to back fit of the angle iron position vs the rear of the Powerstat "big hexagonal nuts" just happened to be perfect. One flat strap was placed upwards left to right on the front side of the angle and the other was placed downwards left to right on the backside. These had to come in and out a few times to trim the ends at angles for a good fit without sharp triangular tabs protruding into the next space, or just to make them fit inside the angle. These little details consumed much time.  I was glad Jacob was helping me. He would trim the ends as I asked, then hand me the next piece, and wrench one end of fasteners, etc. Tell ya what he ain't afraid of work.

Now it may not look very strong in the back end, but believe me the triangular arrangements here, I am confident, will support several times the weight, and should support half of a 100 LB Powerstat until the next person owns the amp, at which point I won't care any more. The triangle arrangement came about due to the effort to make the holes like up. A flat 'hoey metal' piece was bolted loosely to the Powerstat's support spot, and rotated until there was a clear hole at each end. It may be silly but that is how the geometry was determined. It would not have been used if it were unacceptable. I guess there are two schools of construction. One starts with mechanical CAD and precise machine tools. The other starts with a lot of imagination and the ability to stare at something until the imagination calls a few simple solutions to mind.

The only ghetto part of today's work is the stack of washers taking up the space between the 3/8" grade 8 bolt head and the big hexagonal nut. This is the support for the back of the Powerstat. I promise to eventually get a shorter fastener. I believe it is strong enough however and with a lockwasher it will not come loose. I want to add another X or a single angle bracket to give it two support points.

 


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« Reply #28 on: May 15, 2016, 08:34:58 PM »

More pictures of some details.

As for making the Powerstat level, we looked for the level fo 20 minutes, then the bright idea flashed on: The level is the rack. The front and back of the top of the powerstat were compared to holes in the rack using an old panel as a carpenter's 90 degree angle. So yeah this is level front to back with the rack to about 1/32"

It might be asked where the giant potentiometers went. For now, the too-long bolt with all the washers has made it difficult to mount that back on. It will fit but the rotary coupling does not engage well. It never did engage well. The big pot also needs cleaned up and lubricated. The Powerstat BTW responded very well to being cleaned and lubricated. It's very easy to turn. The giant Ward-Leonard potentiometer may be another story because its contacts are held in tension by a powerful spring. It may never be really easy to turn. But should a 14' diameter pot be easy to turn? that is a good question.

Also, although it's nice to have, what would be the purpose of a huge pot like that ganged to a powerstat in an amplifier?  

The plan, the way it is working out now, is to build the HV power supply first, then the mains cable and stuff so incrementally things can be tested.

Until next Sunday..



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Making Amplitude Modulation GREAT Again!


« Reply #29 on: May 15, 2016, 08:41:03 PM »

My Harris uses pots for feedback of where the roller inductor is.

Inductor spins 10 times,  geared 1:1 to a pot that indicates the position of inductor.

Use a motor driven shaft,  and with a simple comparator circuit,  you can have presets of the powerstat (or inductor,  in my case).

Think remote control bud.

--Shane
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« Reply #30 on: May 15, 2016, 09:17:29 PM »

Loving it already - a 55 year old 600 ohm 100W pot as a position feedback pot. Get into that real analog servo stuff there! True renaissance.

It is a great idea. Doesn't matter if the pot's giant, pot's a pot. It's big enough to handle some current so even a simple relay controlled position or something like a 115VDC gearmotor could work. Hadn't thought about remotes but others have said they did it because of blower noise. That is a great idea how to use the pot!

The overall layout seems to be coming to mind too. I learned the hard way restoring the COL Tucker, that one should not try to skimp on space or build a very compact equipment unless one has a lot of time for detailed engineering, knows all about thermal issues and everything else. It's a fine rig but there's no room to add anything and the OM did not put a mod reactor in it. Lesson to me: need one rack, use two.

The plate transformer and blower can sit in the left hand rack bottom. Above them, there will be tons of room for the RF section and the control circuits, filament supply, etc. I do not want to try and cramp that because I will make more design mistakes and compromises and it'll be hard to work on.

The filter cap and choke can sit in the right hand rack below the Powerstat. It should help weight distribution, them poor casters are suffering on the left side. Above the powerstat should be the window for the MV rectifiers. They don't take much depth. Behind them and above them, plenty of space for a built in tuner. That wasn't strictly planned, but it looks like Frank had some luck with the idea on his 3cx3000 and there will be that space.

Thinking about casters, now would be a good time to replace all of them while the plate iron can still be easily removed with the block and tackle. It will only be 10X as much work later.
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« Reply #31 on: May 23, 2016, 06:52:37 AM »

Yesterday's work. It does not look like much, but getting a couple panels to fit so the exact position of the Powerstat panel could be known, and then making up that panel to look nice was time consuming. a large hole was made with a punch in the white panel, the panel mounted in the rack over the Powerstat, then then the round scale put on, its mounting holes center punched, removed the scale, drilled, and tapped the holes, then put it all back.


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« Reply #32 on: May 23, 2016, 06:56:52 AM »

This turned up, a coaxial filament choke, but it is for 10-80M, and more like the size for a 3-1000 or 4-1000. I still have the filament choke from the TMC 10KW amp to use on this one. Found a possible power cord. It's 8 Gauge, may or many not be enough. I have to look it up. Also, some nice red push buttons could be used for the power switch but nothing like that has been decided.


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« Reply #33 on: May 23, 2016, 07:01:19 AM »

Some 70A 250VAC breakers. A set would be perfect for the mains input. They run on DC to 60Hz. I stripped these RCA MV rectifier sockets off a BC-5, but I don't have the 575A tubes I wanted to use. I thought I had some, but didn't find them. I have plenty of 673s and 4 new Johnson sockets.


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« Reply #34 on: May 23, 2016, 11:55:06 AM »

Not sure, but I think that "safe vault" adjuster for the variac sort of needs a slick looking and clearly visible pointer mounted off the bottom of the central part that affixes to the shaft?

I'm thinking a pointer with a round ring as an indicator at the end that goes over the scale area?

Brass would be easy to fabricate, and I think the hobby shops may sell brass rings.
But epoxy and aluminum or even plastic will work too... just need the arm and a way to
mount the ring on the end.

Classy.

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« Reply #35 on: May 23, 2016, 12:21:08 PM »

I like the looks of the safe handle and i see the shaft to the safe handle is insulated from the internals by the U-joint connector...but I think I would prefer a nonconductive steering wheel....Good luck...neat project..
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« Reply #36 on: May 23, 2016, 09:41:55 PM »

There was no pointer on the Powerstat when I found it. One of the handles was the pointer. It may be possible to slip some heat shrink tubing over the handles. Black for two of them and white for the indicating one. It could be possible to make a brass pointer from flat sheet stock or some odd piece of hardware and tap holes in the rear of the wheel hub to mount it.

The 'safe handle' wheel was on the Powerstat when removed from the original equipment. It's a very good point about it being conductive. It is insulated by a ring of about 3/8" wall thickness from the brush-carrying metal disks of the unit. I should make sure the shaft is grounded.

The U joint in the back for the huge potentiometer is insulated mainly because that is the pot's wiper. That has not been reinstalled yet. It's not decided about it.  It is fun to talk about alternate ways to turn the Powerstat, but simple is going to be best. Remote control or cool looking mad scientist style levers and other stuff would complicate this whole thing and with rational thought I would prefer it to be simple because of the realistic time factor to finish it.

We want to replace the casters. These swivel on ball bearings but have no ball bearings on the axles, and some kind of plastic wheels. The constraint is that they are right in the corners and close to the skirts of the rack so going bigger is not likely. Better is possible.
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« Reply #37 on: May 23, 2016, 09:58:45 PM »

There was no pointer on the Powerstat when I found it. One of the handles was the pointer. It may be possible to slip some heat shrink tubing over the handles. Black for two of them and white for the indicating one. It could be possible to make a brass pointer from flat sheet stock or some odd piece of hardware and tap holes in the rear of the wheel hub to mount it.
<snip>

Exactly!!

But I suggested rather than a simple ---> pointer use a circle that is wide enough to show the numbers in the center as the indicator at the end of a pointer :   ----o  like that. 

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« Reply #38 on: May 26, 2016, 03:11:27 AM »

I see. I didn't exactly understand where the brass ring was suggested to go. It would be a nice touch to have it encircle a mark or two on the dial as i think you suggested. Brass is good stuff. It solders easily.

The most interesting home made pointer I have seen had a 'self focus' grain of wheat lamp under the tang of the pointer that it up the marks being pointed to. It was not on a variac but on a large rheostat with a handwheel.

BTW the correct Superior Electric T5587 paralleling choke was found on ebay for $60.

This information could help others - it is simply a roll of steel strap 1" wide wound into a toroid shape with an ID of 2.5" and OD of 4". The windings are bifilar with each having 12 turns of #8. The insulation is rated 600V and 105 deg C. The current rating is 28A per side, same as the Powerstat.
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« Reply #39 on: May 28, 2016, 12:48:27 AM »

Well here comes the weekend! more to do! Saturday I go to the hardware store and then take Mom to church, then Sunday = all day for the project. Time management!

OK last week the circuit breakers were found, some 6 GA wire, Hg relays, and lastly the paralleling choke from eBay is staring me in the face. The selection of breakers is pretty good, all are DC to 60hz, and there are many sizes dual and single from about 10 to 70A.

Those breakers were used before on a 12/24VDC bus and are still wired for that but the wire tying them together needs to be redone because it is not insulated and too close together as well as made on only two #12 solid conductors together. Its a PITA since the 6 GA is so stiff.

If lockwashers (cut washers) are used with the breaker terminal nuts, could an aluminum strip be used as a bus? My understanding is that it is OK as long as the connection can not become loose.

Their mounting has also to be considered because they are in a couple of boxes that mount to the front surface of wall or rack, and so it 'sticks out'. One has to be chosen. Looking for a way to mount it "back-set" so it is somewhat flush.

some idea for the heavy gauge input wiring is attached.

Before that, I want to remove the casters and set the racks on some 2x4 boards until new ones can be had.

Will be a full day, hope it can all get done. Jacob is supposed to come over early Sunday to help.


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« Reply #40 on: May 29, 2016, 10:46:09 PM »

Not everything wished for got done but does it ever? Several things were not available and other things did not fit and had to be modded or maybe fit into the realm of hackery. It's not an issue - it's turning out to be a lot more fun to try and get as much of it from the 'junk box' as possible. There's a large junk box here so why not use i!
 
Mounted some breakers in a nice old Rockwell panel. It was tricky because the panels on-hand mount at the rear and 'stick out' from a rack. To make it flush, rack rail angle was screwed to the internal horizontal supports of the rack cabinet. Only one hole matched up on each side and it seemed like a problem at first. I don't yet have the crimp-on ring terminals for #6 that will be attached to the terminal studs of the breakers and the Powerstat. (The wire will be soldered after crimping). The one-hole mounting means that the panel can be tilted up to get access to the top of the Powerstat to finish the job once the electrical connectors are had.

The breaker panel will be held in place vertically (held down to prevent it pivoting up) by the rectifier chassis. An old 1U 10 base T hub fit the bill to act as a chassis for the rectifiers. Once emptied of its guts, this is a light and strong box. The rack mount 'ears' are not shown, not in place because the sockets are not yet mounted, no holes drilled yet. There will be a 1U panel to cover the 10BT thing so it does not look like a junk box part. I just wanted to see what this will look like before doing the work. Instead of being at eye level, they are a bit lower, as is the Powerstat and the circuit breakers. This is better to observe from a typical seated operating position.

The rack space above the rectifiers is reserved.


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« Reply #41 on: May 29, 2016, 10:53:15 PM »

The rectifier sockets are Johnson part number 123-2026-200. If anyone knows the insulation rating for these I would appreciate it. because it is a bridge rectifier the peak voltage could be fairly high.

There are some 1" tall ceramic standoff insulators that can be used with the sockets in case the voltage rating of the sockets alone is approached too closely.

The project amp should also get this set of nice 'hash chokes' taken from an RCA BC-5.


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« Reply #42 on: May 29, 2016, 11:13:30 PM »

A bunch of really nice #6 wire was salvaged. This is 105 deg C rated, plenum rated, gasoline resistant.

The rack was lifted up onto some blocks and all the casters were removed. They are not too bad looking but these are very well-worn and filthy. They do not have ball bearings in the wheel axles but the swivels are ball type. If it were for something lighter I'd want to just clean them and relube, but I want to find some better ones for this. The originals all swivel and have 2.5" wheels of some hard rubber or some kind of resilient plastic.

Does anyone have advice on what features a caster would have that would make it easy-swiveling? Other than ball bearings in a race, I don't know. I am not a caster expert at all. This dual rack is probably going to be 600 LBs on the left side and 400 on the right side.

All comments welcome! This is the largest piece I have ever tried to build from scratch and I've seen what others have built on here.


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« Reply #43 on: May 29, 2016, 11:18:59 PM »

Lastly, Jacob's Tesla coil is coming along. It's experimental 70KHz RF-driven type with audio modulation.

I convinced him to ditch the microwave transformers and use some 500VA potential transformers instead. They are not the best thing but were free and make 2400VAC. These were tested before and have good regulation with the 'burden'.

Two modified tube-type regulated supplies are to be tried with this. One is for the grid to make bias and provide the 70KHz drive signal. The other is for the screens and should be the 'screen modulator'.


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« Reply #44 on: May 30, 2016, 08:56:21 AM »

Way kuhl so far!
Say, what's the light green meter panel from?
Reminds me of the Birdwell (div of SSC /Raytheon) pwr supply panels I used to use at Nevada NTS back in the 60's.  All our stuff including the logging trucks used that color.
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« Reply #45 on: May 30, 2016, 10:00:12 AM »

The casters provided on my "surplus store" cabinet were never rated to support the weight I provisioned, and ultimately collapsed.
 
Mcmasters had a replacement that was an exact fit for the mounting method, @ a load rating that worked.

http://www.mcmaster.com/#casters/=12mw2mr

Wish I had changed them "before" filling up the cabinet  Roll Eyes
73
Frank
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« Reply #46 on: May 30, 2016, 10:28:30 PM »

Way kuhl so far!
Say, what's the light green meter panel from?
Reminds me of the Birdwell (div of SSC /Raytheon) pwr supply panels I used to use at Nevada NTS back in the 60's.  All our stuff including the logging trucks used that color.

The light green panel is a Lambda tube type regulated power supply. It will be modified to serve as a bias supply and 50-100KHz RF grid driver for three 4-400s. There is another regulated supply of about 500V coming. This will screen modulate the 4-400s and give the audio signal to the RF discharge. We hope it will be clean sounding. These kinds of mods are not complicated.

It's turning out that by two persons cooperating to do two projects, both projects are easier to do because help is always available. An extra head and pair of hands goes a long way.

The casters provided on my "surplus store" cabinet were never rated to support the weight I provisioned, and ultimately collapsed.
 
Mcmasters had a replacement that was an exact fit for the mounting method, @ a load rating that worked.

http://www.mcmaster.com/#casters/=12mw2mr

Wish I had changed them "before" filling up the cabinet  Roll Eyes
73
Frank
KJ4OLL

What you experienced is what I am trying to learn from. Once that plate iron was in, the rack acted like it was on feet, not wheels.

Thanks for that link! If I don't find them locally they have what is needed - just need to measure. This rack has skirts so the diameter of the wheels is limited. The stock wheels are 2.5" diameter and 1" wide with sleeve bearings. I prefer the larger wheels and better bearings because they swivel easier and give a little more clearance. Clearance is important if the gear has to be rolled over a threshold etc. Racks also need to be able to be moved around to sweep the floor because all kinds of dust and junk collects under them.
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« Reply #47 on: June 05, 2016, 09:21:08 PM »

Looks like the McMaster-Carr 9908T19 should work. They are only $12.45 each. There was found no other caster that would fit, and be easier to push. This one says it is more about durability than ease but the amp is not going to be rolled around much.

Today's work does not look like much was accomplished but it took some time to map out and drill the holes for the rectifier sockets so it would be straight and neat. It all has to come apart again for wiring but the major mechanical stuff is worked out.

The picture of the front with rectifiers is what it looks like when seated.

I still have a question about those Johnson sockets and their voltage rating. No catalog so far has given an answer.
Seeing that it is a bridge, two will be at B+, but two will have the AC on them and the peak voltage could be more like 8500V to GND. The clearance from the pins to the metal chassis is just 3/8" and I think it is marginal.
Should I add some short standoffs under the sockets?


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Patrick J. / KD5OEI
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« Reply #48 on: June 05, 2016, 09:34:37 PM »

The rectifiers are easily spaced in the width of the rack. They fit well with centers 2.5" apart. I had a panel with a large cutout for the viewing window over this but it seems to be hiding somewhere.

The rack-front picture s the view while standing. Looks like a good compromise. Mounting the rectifiers too high would have made them hard to see when operating, which to me is the more important view.

The third image is Jacob's Tesla project. Today it was a mechanical layout day to fit the main units in and for the big power supply at the top, a set of rails were made from punched angle iron. Two right-to-left pieces underneath help support it. The power supplies still have to be modified and most of the stuff behind the panels wired up. It all fits. There is another chassis for the tubes, not sure where they are going. Maybe on top.


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« Reply #49 on: June 05, 2016, 11:37:10 PM »

Patrick,

According to this chart,  you should be fine....

0.175"                7000         
0.250"                9000       
0.350"                11000
0.500"                13000

Your looking at a .375 inch spacing,  if it's 3/8.

You should be good for slightly over 11kv.

Not a lot of room for dust mites,  hair or dander,  but it should work.

--Shane
KD6VXI
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