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starting work on the amp




 
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Patrick J. / KD5OEI
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« Reply #275 on: July 22, 2017, 09:00:32 PM »

got to spend a few hours on it today.

I moved the PVC pipes that conduct the GTO-15 HV cables from the rectifier tubes to the transformer and filter. Moving them 6" to the front made room for the 4" duct to easily pass through to the level where the tube chassis should be. I was lucky and only had to flip the brackets 180 degrees and there was enough loose wire so nothing was stretched. The brackets are a flattened "c" shape with a tab.

For now I put the 4" aluminum duct in. It was a little chore but fits well because it bends and stays bent. PVC will be explored later if things are too noisy or hot.

To bring the air up from the bottom, the amp chassis will have to be elevated so the duct will fit. Doing it from the back, it should fit right in. It seems like it would be easier to deal with later if it enters by the side or back. It should never need servicing but it will sure need tweeked.

This said, the RF chassis will need to be moved to the back of the rack. It's not a problem because it only contains the tube, socket, input jack, metering pickups, and the filament choke. Aside from the calibrations for the grid and plate current and filament voltage meters, there are no controls on it. The turns counters are there but not likely to be used. I think the original plan to put 6 Meters on this is too ambitious. The plate circuit components will be separately mounted but as close as
they would normally be.

I'm learning a lot on this project. It's quite different than what has been done here before. Lots of good ideas an examples from stuff already out there.

About the RF chassis - there are apparently a couple of open wires in the factory wiring loom. Glad this was checked today and not assumed it was good. All the un-used holes, a lot of them, have been sealed with that aluminum/metal tape normally used for ductwork.

Fired up the HV again to check the new inrush resistor value of 10 Ohms. It's great. The same 3 resistors were used just put in parallel.

A glitch resistor needs added. I have a box of 50 Ohm 200W units coming in the mail. They were free for the shipping! How many should be used in parallel? maybe 2 of them? I think 25 Ohms is a decent value.

I probably should be putting resistors in series to share the voltage better. There is 5KV. What do yall think about glitch resistors?

There is also a #30 wire in the plans for a HV fuse. Do I need both? Should it be #28 for a 2A plate current?


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« Reply #276 on: July 22, 2017, 09:16:00 PM »

This table shows fusing current for various times. One is 32ms.  How fast should a wire fuse in the anode lead blow out in case of an arc in the tube?

https://en.wikipedia.org/wiki/American_wire_gauge#Rules_of_thumb
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« Reply #277 on: July 22, 2017, 09:24:36 PM »

I used 50 ohms at 800 watts.

4 X 200 ohm resistors @ 200 watt each.

Big wire wound jobs.

This was in use with a 32 uF oil filled cap and a 12 kva ccs Dahl powered supply.

There are pics, I believe, on the thread I started about it.

--Shane
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« Reply #278 on: July 24, 2017, 12:13:42 AM »

That sounds pretty good to me.

Are these the ones or did you put 200W ones in? Very tidy assembly here.
http://amfone.net/Amforum/index.php?topic=41800.msg304387#msg304387

So that's about it then for the glitch resistor. I'll do the same thing or something like it but have to find space for the units as they are pretty long.
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« Reply #279 on: August 06, 2017, 10:19:35 PM »

Before the RF chassis can be installed I have to know the 'desired' meters will work with the plate and grid current shunts that are present. If not then use larger shunts or smaller meters! These two meters have 5 Ohm DC resistances and need about 3mA to go full scale. Hope the others are similar in regards current and resistance.

OK well my helpful assistant has put the box of the rest of the Westinghouse 'RCA Transmitter Meters' away somewhere and after 2 hours I could not find the box.

The two shown are the RF ammeters, which I probably won't use. c'mon 20A!! 10A is 5KW on 50 Ohms, but with a tuner the Z therefore the current could be anything. No thermocouples for them anyway.

The thing is, these RF ammeter movements are not linear. I believe they would have been calibrated individually with the accompanying shunts, which are long gone never had them.
Here are the scale readings vs. mA DC through them. Used a 10K resistor and h/p 0-40V supply to get my bearings. In the end they are ~3mA full scale deflection. These (the rest of them) will clean up nicely assuming he remembers where he put them!


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« Reply #280 on: August 06, 2017, 10:55:02 PM »

Some 50 Ohm resistors which arrived last week were opened and out of 17, 4 are cracked. They still check OK and maybe I will use a sleeve and epoxy to fix them later just for fun. The 'glitch' resistor can use 4 or 6 of them as in two parallel stacks, for a total of 50 or 75 Ohms. I would not want to go too much more since the resistance will drop the plate voltage with current, the resulting poorer regulation causing slight compression of modulated signal peaks. That is only worth bringing up because this effect is a cause of distortion and the plate supply already has very outstanding regulation.

An interesting factoid shows up when the broken resistors were examined. The Ohmites, which are fixed/non-tappable have what appears to be nine resistance ("novafilar" winding?) wires and the HEIs, which are ther type that can be tapped with a sliding clamp, have one wire.

Which is better for taking that huge voltage spike and surviving the 390 Joules when the 100A or 67A glitch happens? No sane way to check that I guess. Nit picking?

The glitch resistor has to be mounted insulated from the chassis because it is in series with the plate supply voltage. A glitch/bleeder combo from some other thing can be repurposed. (I think it was from a satellite uplink transmitter klystron supply, 3500W on S band.) The glass epoxy material looks a little overheated but is well within usable condition and will not be heated in its second life. A couple of thick ceramic stand-offs should mount this up once the new resistors are put in it.

Both types have similar ratings:
Ohmite 270 series:
Overload 10X for 5 seconds (335V@50R)
Body insulated to 4595V

Vishay AVT:
5% tol.
AVT-200 = 225W
Overload 10X for 5 seconds (335V@50R)
Body insulated to 1000VAC


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« Reply #281 on: August 06, 2017, 11:16:04 PM »

A couple of 25uH 15A variable inductors were found. They have a shaft on each end and should be easy to use later for a tuner. They will be put aside for now.

I have some questions about the tarnish -does this act as an increased resistance or is it of little concern? Would it make sense to dip the parts in tarn-X or something?

How are these flat ribbon types units cleaned since you can't get into the coils contact area easily?

Is there a special grease for them?

There is a 'tight' or harder to turn  spot as the roller goes through a 360 degree turn. I loosened the screws that support the coil and put the roller to the tight spot, and the support moved a bit. Re-tightened in that new alignment - seemed to fix it. What causes this to happen? Someone drop the part or bang on it? They look in good condition otherwise.

The wheels in them look adjustable -notice the threads on the hubs. The small indentations on the hub 'collar' seem to be for a special wrench. One of them has a set screw in it. I don't want to fiddle around with that. Any time a special wrench is implied, it's easy to break something.


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« Reply #282 on: August 09, 2017, 09:48:40 PM »

I'm told the tarnish, silver oxide, is a very good conductor so I guess I'll leave it. Lots of warnings about Tarn-X being acidic.

What is a good lubricant? Some people recommend Molycoat, a dry lubricant with Molybdenum Disulphide.
https://www.lawsonproducts.com/Lawson/Moly-Coat-Dry-Film-Lubricant/92964.lp

What will not harm the silver plating?

I noticed the 'wheels' the rollers are made of a few materials, looks like some aluminum and some steel-like or tin-like metal discs.

I really need some good advice here and have no doubt there are knowledgeable persons about this subject on the board. I searched cleaning edge wound variable inductors and got no result.
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« Reply #283 on: August 10, 2017, 02:21:27 PM »

I used the wash and lube that was available at radio shack when I had to lube and clean my roller in the Harris.

Don't think it's available now, though.

--Shane
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« Reply #284 on: August 10, 2017, 02:47:50 PM »

Black silver oxide is nearly as conductive as clean new silver, which is why it's preferred as a coating for rotary inductors.  Skin effect currents actually flow deeper than the plating, so the silver basically acts as a preservative for the substrate material.  For the contact, the only place that connection resistance matters is where the coil and the wheel come together.  If you keep this area free of grease and yuck, you'll be just fine.  The coil surface and the wheel need to be free of burrs so that they will remain in close contact at all times. Everything else is cosmetic.  I have used Tarn-X a couple times, but the ammonia smell will knock you over.  Multiple rinses will solve any residue problems.  Calgon dishwasher detergents works well, but you will need to carefully relube after things dry out as they clean oilas well as they clean last night pork chop dinner plates..  If the ceramic is fairly spiffy and the coil isn't covered with gunge, it's OK the way it is.
Those Kintronic inductors are nice.  I have used their big brothers on medium wave systems all over the world. Take good care of them and your grandchildren will be fighting over them some day.
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« Reply #285 on: August 11, 2017, 01:57:03 AM »

That's good news! Too bad it does not apply to oxidized copper.. I had to spend a few hours on a couple other coils of that material and now they are as shiny as a new still.

The only remaining thing, in two parts or aspects, is that there are a couple places where the movement/rotation is 'tighter' and the rest is fairly free; and that when I turn the shaft  through 360 degrees quickly, there are a couple of areas on a few turns where it seems contact is lost but if I go slowly, this does not happen. Considering the 360 degree rotation, the lost contact happens when the friction is least.

The picture shows the wheel. This turns apparently by friction between the two thin 'flanges' as the offset shaft moves in a circle. When the loose contact thing happens, it is always where the wheel does not turn, it stops and slides along for an inch or two. Hand in hand with this, the 'tight' places are apparently where the 'hub' of the wheel must be riding against the inside of the coil.

There is a small amount of play between the outer edges of the coil and the three grooved mounts. This may be able to be tightened up or loosened a little, and I tried this but it does not change the loose contact at the couple of places where it is an issue.

I can't see where the coil is damaged in any way, no evidence of bring dropped or hit, or anything else. What should I expect/inspect to understand this better? Is it even related to the intermittent 'loose' contact when rotating quickly?

I think I should try to slightly 'bend in' or cause the flanges to grip the flat sides of the coil harder. Bend is not the right term but how do I fix this?

It is an issue, sometimes we crank slow, sometimes we crank fast, sometimes we use a motor!

And thanks for yall's good advice on this slow moving project!


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« Reply #286 on: August 27, 2017, 01:15:23 PM »

The rollers are put aside for now and the meters have been found and checked. Four similar sized meters were also found and checked.
All the DC current meter seem to have internal shunts, so they direct-read.
The RF ammeters (previously discussed) are missing the thermocouples.
The AC voltmeter has a small multiplier and relies on a larger external one.

All are Westinghouse. I have looked for a Westinghouse catalog to learn more about the meters and their part numbering schemes, but in vain.

Maybe these data points will help someone else.

image of 4 meters:
height 4" width 4.25", mounting hole about 3.75"
bakelite or plastic case
1) 4A scale, 4A full scale deflection, Type QX-37, Style PH-16164-1
2) 400mA scale, 400mA full scale deflection, Type QX-37,  Style PH-16166-1
1) 200mA scale, 200mA full scale deflection, Type QX-37,  Style PH-16182-1

image of of 14 meters:
2) RF ammeter 20A scale (ext TC not present) movement 5 Ohms, 3mA full deflection. Current not linear to scale marks. Type KT, Style N-636902
1) 20mA scale, 100mA full scale deflection, Type KX, Style XN-66146-3 100mA shows 20 on scale. Has overload relay circuits on back.
1) 200mA scale, 200mA full scale deflection presumed, Type KX, Style NY-712442-1 (movement not moving, dirty?)
1) 300mA scale, 300mA full scale deflection, Type KX, Style NY-66146-3
2) 600mA scale, 600mA full scale deflection, Type KX, Style NY-66146-6
2) 800mA scale, 800mA full scale deflection, Type KX, Style NY-66146-4
1) 2.5A scale, 2.5A full scale deflection, Type KX, Style NY-89576-1
3) 5A scale, 5A full scale deflection, Type KX, Style NY-66146-8
1) 3KVAC scale, 5VAC/1mA full scale deflection, Type KX, Style NY-66146-8, uses external multiplier

The glitch resistor bank was made up with six 50 Ohm 225W resistors to make up a 75 Ohm heavy duty resistor, but might be changed to four of the resistors for a 50 Ohm unit, in order to put the HV wire fuse on the same assembly. I have an idea how to enclose the wire so that if it explodes the pieces might be contained and also how to make it easy to replace the fuse-wire. The mounts for the resistors are two pieces of very thick epoxy-fiberglass board. One end has holes drilled with metal threaded inserts so that screws can be fit into it, and it can easily be mounted. The question is only where to mount it out of the way.



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« Reply #287 on: August 27, 2017, 02:02:42 PM »

Also found a nice handwheel and these little vacuum tubes. Wonder what they are for? Notice the shield above the upper plate. It's a "discharge tube" made by Goodrich industries but I don't find any info on specs.

cage code K4358, NSN 2920-00-190-4301, 2920001904301, maybe also called "DG 71".


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« Reply #288 on: August 27, 2017, 02:17:26 PM »

http://w2dtc.com/w2dtc-plasma-amp/2010-0225-hv-fuse.jpg
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« Reply #289 on: August 27, 2017, 02:40:06 PM »

I saw that, and there is a picture of another one on two cylindrical posts somewhere.  HV fuses are a great idea. I just want to enclose it for safety reasons. It might not get done so elaborately as the drawing by the time it gets made up.
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