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Author Topic: starting work on the amp  (Read 185977 times)
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Patrick J. / KD5OEI
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« Reply #75 on: July 17, 2016, 06:50:20 PM »

Jacob liked the buzz from the Plate transformer and I had to agree completely, a sweet and endearing sound! - Mellow and relaxing, yet not without a hint of ball bearing pie with a slice of clack. - So we recorded it as a sample being brought up on the powerstat as well as with the sudden application of 240V and the Ungh/Bonk/Huzz type of sound we all know and love. A couple of times it shot the clamp-on's needle to the top of the 50A scale so the peaks must have been a little larger than desirable. Soft start will be a must on this just out of politeness to the rest of the house. Maybe I can post the samples later once Jacob sends them over. I am sure you will like them.

BTW for those that don't know, Hg contactors are nearly silent. No kerchunk with those.

pr0n of the 4KV Tesla power supply and modulator is shown as well. Top to bottom: Audio modulator and screen supply, RF driver and bias supply, Plate voltage control, Plate supply and filament control. There are three plate transformer + rectifier sets, one for each 4-400. The DC filter will be in common.

We are not drunk on power. We just like electricity. These are all completely normal and wholesome Sunday afternoon activities for today's nuclear family. God bless America! One of few places in the Free World where you can make whatever you want!


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« Reply #76 on: July 18, 2016, 10:38:17 PM »

Nice work Patrick and great attention to detail. I thought I was good but I never thought of matching color shrink tube over crimp on connectors. Good job.
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« Reply #77 on: July 21, 2016, 12:03:09 AM »

Thank you. It was on hand so why not? Truthfully the other end of the cable is plugged into a 50A outlet so the tubing gave me a little better chance to avoid a short. I got the tubing years ago, bought several packs in different diameters each with an assortment of red, blue, green, yellow, white, black, and clear. The 8" pieces, two in each color, this was a good investment. I want to go back and put some on the other leads too.



Someone suggested that the buzz and 5A draw is because I am running the transformer on single phase, not 3 phase wye 208V or 240V, meaning that I'm putting too much voltage into the primary.

Instead of 240V across each primary winding he suggested I use 139V. That is, divide 240V by 1.7333 to arrive at the voltage that would have been there normally on the primary winding assuming the wye input.

Now, the transformer says 208 and 240V on its connections.

Putting 120V to the 208V taps  is the same as putting 139V to the 240V taps. I'm not explaining well but what I am trying to say is:
208V wye = 120V from phase to neutral
240V wye = 139V from phase to neutral

I do not have the schematic of the transmitter it came from so I do not know what the hookup options are.
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« Reply #78 on: July 24, 2016, 10:56:59 PM »

The small wires from the breaker panel to the back of the rack were done, as well as the wiring from the Hg contactor coils. These are going to a small terminal strip at present. The way is now clear to start building up the rectifier circuitry starting with the MV rectifier chassis installation and wiring the filaments mounting up the Dahl FWB filament transformer then the silicon stacks. Time to get out the 15KV wire for that stuff. I have lots of red and green 600V wire, hardly any black or white in the appropriate gauge so.. maybe it will be done by Christmas.


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« Reply #79 on: July 24, 2016, 11:01:24 PM »

The magnetizing current issue with the plate transformer was checked by measurement. A graph shows how it is low then increases more quickly as the line voltage goes above 136VAC. This is the possible saturation issue and the cause of the hum from the unit. The vibration can be felt on the rack. Unfortunately the HV AC is too low to do much with unless the saturating and humming is allowed, so trying to think of remedies for it.

One graph shows the primary voltage vs. current (no load) normalized to 1.0. the next shows the deltas between voltage increments and current increments as the voltage is raised through a range. I'd appreciate any suggestions. The chart is the measurements.

One idea could be to add a separate additional transformer and bridge making 1KVAC@2A with a separate bridge and put that between the low (-) side of the main supply being built, and GND (B-) Two 240 x 480V 1KVA control transformers in series might do the job.

Another idea could be to wind some turns around each of the well-insulated windings of the existing transformer, there is room. Put them in series with the existing secondaries. Might be risky. Don't know the turns per volt yet.

net net is I need 5600VAC.





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« Reply #80 on: July 24, 2016, 11:11:09 PM »

On the Tesla side, the other project, some work was done with the Lambda 481-C supply to modulate it for use as a grid driver. It's not correctly amplifying the 70KHz carrier signal yet but it did self-oscillate at 145Khz making a 400V p-p signal across a 50K load so it looks good. The self oscllation was able to be lockes to the generator. It was found that the reference regulator was igniting and extinguishing during large output excursions. The reference regulator and error amps need their B+ changed, from a source linked to the regulated output, to an unregulated point so they are not directly powered by the DC output loop.



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« Reply #81 on: July 27, 2016, 01:41:19 AM »

update on the plate transformer - -it has two primaries and two secondaries. A test can be done with one primary then the other, to check the current and secondary voltage.

On the power supply mod, the paragraph about it would be clearer with this schematic.


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« Reply #82 on: July 30, 2016, 05:23:29 PM »

The problem with the high current on the transformer has been found and fixed.

When the transformer was reassembled from a three phase unit into a single phase unit, the 208 and 240V wires for one primary were put on the terminals reversed. The terminals as previously shown are on a large insulating board. This was not very evident because the primaries should all be made the same, that is, wires from right to left should be the same taps. However, it was seen that as the taps progress from inside to outside, they are not in the same order right to left on both bobbins. The 240V wire is closest to the core, then one layer after, is the 208V wire.

The testing of the transformer was done as shown in the diagram, hence the unusually high current due to one winding having more turns in use than the other.


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« Reply #83 on: July 31, 2016, 12:36:27 AM »

All well & good, that must've happened in shipping Roll Eyes

73DG
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« Reply #84 on: July 31, 2016, 09:51:34 PM »

That out of the way, more was done. The 240V and +11V taps gave right at 5660V secondary with the full 220V coming from the Powerstat. In the summer it tends to be 220V not 240V here. The primary current is just 1.75A which seems fine on a 20KVA transformer. I previously misquoted the KVA rating at 13-14KVA because I did not see the label properly. The rating was reduced to 20KVA from an even higher value when the transformer was reworked to single phase. So it's a 20KVA unit, fine with me as someone may want to use a larger tube in the future.

The power cable could not stay connected to the main breaker for testing because the rectifiers had to be put in. A run of #6 was added between the breaker and a temporary terminal block in the back, and the power cable was moved there. The ground from the power cable to the rack frame was also added and the neutral is now also conveniently available for more test-as-you-build fun.

The Mercury vapor rectifier chassis is now mounted in its place and the PWD "575A Bridge" filament transformer was put on a 1/8" steel panel and mounted sideways inside the rack between the front and rear rails. Despite steel being used, the heavy filament transformer will wobble or oscillate the panel a little if jarred. I would like to find an "L" shaped material of the same length as the panel and mount it on the back at both ends and the center to stop that. It's not really a problem but I don't like things moving.


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« Reply #85 on: July 31, 2016, 09:52:22 PM »

I am happy to find out the real rating of the transformer is 20KVA!  The regulation should not be changed and be around 2-3% from tube idling current to full current. The ripple might be about 12v or 0.2%.


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« Reply #86 on: July 31, 2016, 09:52:47 PM »

PWD filament transformer for 575A bridge. Each tube 5V@10A. The 673 is the same tube except the base.


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« Reply #87 on: July 31, 2016, 11:33:31 PM »

mercury vapor Rectifier hookups
gas rectifier hookups

RCA TT-4:
1.) When two gas rectifier tubes have their filaments connected to the same filament supply the filament shield or anode return side of the filaments must go to the same filament supply terminal.
(Note that some old-design or low-power rectifiers of these types do not have the shield feature. It is still wise to connect like pins together. -ed.)

2.) For gas rectifier tubes in parallel, it is necessary to use an impedance in series with the anode.

In the case of a resistor, it should create an average voltage drop of not less than 50 Volts.

In case of an inductor, a value of 1/6 henry should be used for 50-60 cycle operation. Inductances are preferred because they minimize power losses and help to limit the peak anode currents.

Center tapped inductors (interphase reactors) can be used as stabilizing elements for pairs of parallel tubes. These inductors assure simultaneous starting and equal division of current.

3.) For gas rectifier tubes in parallel, corresponding filament terminals must be connected together. Failure to do this will cause unbalanced voltage drops in the tubes and make it necessary to use undesirably high stabilizing impedances.



I have also read somewhere that when two gas rectifiers are used without a center tapped filament transformer, the filament shield (anode return) pin must be used as the B+ output terminal. It only makes sense. -ed.

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« Reply #88 on: August 02, 2016, 12:30:29 AM »

If anyone has the schematic for the Sorensen 500-BB "Nobatron" tube type regulated DC power supply, we would appreciate it. It is to be modified as the screen supply for the Tesla coil. A smilar model schematic might do as well.
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« Reply #89 on: August 06, 2016, 06:20:22 PM »

Some thought given to soft start and mercury vapor warm-up and parts on hand. There's a box of really cool Freeman time delay relays here. They are pretty old but elevator grade. They need the the electrolytics replaced after what must be a few decades, the schematic was traced out. Some cap-goop can be seen around the back capacitors.

These are really classy - 7 pin pillar base and 0.5 to 60 seconds. Made in Fort Worth, Texas. The only sockets I have are phenolic types from old radios. I would prefer ceramics or heavy duty plastic ones.

If that falls through there are some Potter Brumfield AMF types that take octal sockets. Two are 5 seconds and one is adjustable to 180 seconds.


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« Reply #90 on: August 06, 2016, 06:21:06 PM »

more


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« Reply #91 on: August 06, 2016, 06:22:37 PM »

more


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« Reply #92 on: August 06, 2016, 06:24:30 PM »

It might make sens to use the newer PB units. Some matching octal sockets were found. Still, if I can get the right 7-pin ones I would prefer that.

A bulkhead mount power cable connector was found in a box of junk. This may be the solution to not having a pesky power cord permanently attached to the back of the amplifier.


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« Reply #93 on: August 07, 2016, 09:21:48 AM »

Be careful Pat. If I understand the idea is to mount the receptacle on your transmitter and use that to attach and remove power. If so the power cord would have the wrong gender. Your extension cord would have the potential of having exposed power pins. I know the pins have a skirt surrounding them but the skirt is just to protect the pins from damage. Just a thought Pat, not a lesson.  Roll Eyes
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« Reply #94 on: August 07, 2016, 11:56:28 AM »

I have to agree with Mike.   Those Hubbell connectors are designed to have chassis mounting on both ends.   You hook up the appliance first,  then hook it to 'shore power'.

That last line should give ya an idea of who they are designed for.   Extension cords for marine.   At least,  that's what I was told when I pointed the same thing Mike did to a boss once.

In your application,  since you know the danger,  you should be fine.   BUT,  another disconnect,  maybe the clothes dryer or stove outlet style on the other side would be a GREAT Idea.

--Shane
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« Reply #95 on: August 07, 2016, 09:46:37 PM »

How about that. Well you guys are right. Maybe I can find a less impressive and more safe connector just in case someone else is eventually involved. Sure is pretty though.

The idea was a detachable power cord. There will certainly be a stove/dryer plug, NEMA 14-60 at the wall. The outlet is already installed to run the Tucker.

I've seen the reverse of that polarity - holes on the cable end and pins on the bulkhead end. My M35A2 project used that sort in a 100A size. What I recall most about it was the price.
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« Reply #96 on: August 08, 2016, 01:45:30 AM »

It's needed to get the controls and soft start working before going forward with the power supplies. Instead of waiting to find possibly unobtainable 7 pin ceramic sockets (like for the 1625) and refurbishing the 1-amp Freeman relays it was decided for now to install good quality standard 50's vintage US-made Octal sockets on-hand and the 10-amp Potter & Brumfield time delay relays. One is a fixed delay of 5 seconds and one is variable 1 to 180 second unit. The 5 second unit should be able to be modified for 1 second and that is what is wanted for soft start, more or less. The variable one is for mercury vapor warm-up timing. The relay types might change later but for now that's what's going on.

From left to right on the panel is the filament transformer relay, the soft start relay, the MV rectifier filament warm-up delay relay, and the interlock relay that prevents anything from happening until the airflow switch closes. A keying relay might be added. It's maybe just a matter of interrupting power to the soft start relay coil. A key jack or terminal can be used but the circuit is 120V and it would be better to use a lower voltage and isolate it from the line.

There is room on the panel for terminal strips. One will be the 10-position one previously shown that connects to the control and filament breakers and the coils of the main and soft start plate contactors.

The sockets were mounted on the surface of the panel rather than below it because the panel is thick compared to a chassis and sinking the sockets below it caused interference between the bodies of the relays and the heads of the fasteners. Countersunk fasteners could have been used but were not on hand.

Because the two time delay relays require the sockets to be at 90 degree rotation from each other, it should be impossible to plug in the relays into the wrong sockets. Their pinouts are also different.


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« Reply #97 on: August 08, 2016, 03:28:14 PM »

Fascinating power plays!
I've been watching your progress from the start and have learned a lot,  Even in detail, e.g.,Your Lambda power supply even has a neon "fuse out" neon lamp indicator across a fuse.  I'd never thought of that.

All Just amazing. But I did modify (t=rc) a P.B. 10 amp octal time delay relay for plate voltage timing specs--. A long time ago for my twin 8875 amp before updating whole thing  with GM3SEK triode control board along with matching power supply mods.
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« Reply #98 on: August 08, 2016, 09:36:08 PM »

Lambda never did cut corners. The neon across the fuse is built into the fuse holder's cap. Very nice! Somewhere there's a box of triple fuse holders with neons in the caps - but the trouble is making the precise 3-phase holes they need in the panel.

Glad to hear that the timing adjustment was possible on a similar relay.

The sockets on the panel have not been wired yet. There should be some surface mount Octal sockets coming. A row of those would look pretty nice and let me use a couple more relays as well for example a keying relay with a 12V or 24 V coil. The real advantage in surface mounted sockets is having the terminals above the relay panel because that's where the rest of the terminals will be. I need to find some DIN rail as well because a bunch of new-in-box AB terminals for that showed up. It would look nice to have them instead of the black terminal strip.
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« Reply #99 on: August 11, 2016, 12:12:25 AM »

The schematic for the power supply area (attached) has changed a lot since the work is under way. The timing relays are rated 10A so that eliminated intermediate relays. There will be a couple more relays in the power supply for keying etc. but this scheme here should make it impossible to bypass the rectifier filament delay or soft start no matter what order the breakers (as front panel switches) are operated.

I need some advice on picking the inrush resistance.

Right now it looks like an 4 to 10 Ohm resistor may do to limit the inrush to no more that the 'full power' current while letting the supply charge up most of the way.

The tube is going to be unbiased, and should draw 230mA at 4800V, and that is why the voltage won't charge up all the way with a large value inrush resistor.

I had not given that much thought. To what percentage of full voltage should the power supply charge through the soft start resistor? 80%?
A small resistance lets it charge more, but too large a resistance may cause a surge when the soft start resistor is bypassed because the cap is not well-charged..

Some values for inrush seem to be like the numbers below. It's not the easiest thing to calculate accurately but I think it's close.

The concern is the large current (wattage) spike in the inrush resistor. The wattage averaged over 1 second is reasonable but the peaks are nuts! The simulation says the 31uF cap should charge through the 30H choke in much less than one second. A minimum of 0.1 second with no inrush protection and up to half second with a 14 Ohm resistor. It seems fairly proportional in between but my calculations are not perfect.

What really determines the peak wattage the resistor can take? I suppose the mass of its wire has to do with it. Can this be averaged over 1 second without blowing the resistors to pieces? If so, great! a couple of 200-300W resistors could do.
A ceramic heater element was considered but those have a pretty high resistance when cold and does not seem so suitable for inrush limiting in something this size. Maybe a bank of 1KW projection lamps could serve due to their very wide resistance change. There is a box of them here and they probably would stand up to the duty. I'm looking for guidance on this. Don't mind being creative.

The normal bleeder load (tube idling) voltage should be 5020. -the first line represents that. The cap is storing 380J at most. (31uF/5KV)
It is a 4800VDC @ 2A supply and that is 56A@240V so it's a drawing little more current than on some units.

- inrush resistor 0 ohms
- peak inrush 145A from simulation
- peak resistor power 0W,
- peak secondary current 5A,
- HV 5020V (100%)

- inrush resistor 4 ohms
- peak inrush 60A
- peak resistor power 8441,
- peak secondary current 2A,
- HV 4670 (93%)

- inrush resistor 8 ohms
- peak inrush 30A
- peak resistor power 5710,
- peak secondary current 1A,
- HV 4172 (83%)

- inrush resistor 14 ohms
- peak inrush 17A
- peak resistor power 3824,
- peak secondary current 0.62A,
- HV 3670 (73%)

- inrush resistor 20 ohms
- peak inrush 12A
- peak resistor power 3160,
- peak secondary current 0.41A,
- HV 3160 (63%)

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