starting work on the amp

[Opcom]

Today's work. For one thing it is a landmark. Today, Mercury was vaporized.

Finished understanding and marking on paper the terminal barrier strip on the 'electric brain' panel. There was a problem because of constant interruptions and I forgot what I did. Time to write it all down.

Wired up the mercury vapor rectifier filament transformer today. it was more of a chore than thought.. about 4 hours work.

Each tube filament has its own pair of wires going to the transformer. 14 GA stranded wire rated 15KV outdoor duty was used. Luminous sign wire.

The tubes' wires are color coded with 1/4" wide bands of heatshrink tubing. It is therefore possible to troubleshoot easily, with 8 wires going from the tubes to the transformer. The 'cathode shield' pin of each tube is further identified by a white HST band.

The cable of eight of those 15KV wires was not very pretty, could not be made 'squared off', so it was run through the 'wall' of the rack, through a modified rack panel made of insulating material. Between the two bolted-together racks is a space about 3" wide. So, the insulating material 'wall section' hides the wire. The wires come back out just to the left of the row of MV tubes. This was a great help to making a tidy and orderly appearance. It also cost nothing but labor, in keeping with the "junkbox/rat" theme.

Today's pictures showing the MV tubes show the operation with filaments on and Mercury vapor cycle running. I am very pleased but tired. Next logically should be the high voltage work.

I have been thinking about adding 120 or 240V LED indicator circuits inside the amplifier, across each controlled item so that the state of any section can be known at a glance. This would be for a troubleshooting aid. Why not? Modern systems based products have many lights inside to show what the relays and VFD and PLC are doing. Most of the few LEDs needed for this beast could simply be mounted in the 'brain' panel. Later for that stuff.

[Opcom]

and

[Opcom]

lastly,

The insulating panel cut outs. I hope to eventually enclose the MV rectifiers in a box of some kind with a little forced ventilation. Just an appearance thing. It would be nice to have the inside of it black so when it is looked at, the tubes and glow is seen but not the whole inside of the rack there.

[Mike/W8BAC]

When I rebuilt the 20V-3 it was important to me to keep it original. That decision meant MV tubes a priority. The reward is to watch the violate vapor dance with modulation peaks. rewiring the MV sockets was an experience I don't care to repeat. I lost track a few times of the circuit polarity and studied the schematic until I was totally confused. In the end the wiring was right! a proud moment. I replaced all of the GTO wiring and even learned to knot and string the loom like the original. It is not visible to anyone but me. Like you, looks are important!

Mike

[Opcom]

Today no physical work was done but the inrush setup was decided. The low values I wanted which would allow the unit to fully charge in a few cycles would not be acceptable with this filter. It would be OK with a capacitor-only filter. A compromise with a larger value to soften the rate of change of magnetic field in the 30H choke looks like it would only require a delay of about 0.2 second and charge to 90% of the voltage with the tube running idling current so it's no great sacrifice.

Because the power supply uses so a large choke in order to give best regulation, the inrush will cause a high voltage pulse at the output of maybe 8800-9500V (third file) unless the current during inrush is limited to a small fraction of the operating current. It looks like a resistance of 1800-2200 Ohms in series with the plate transformer secondary would do. This with the 25:1 turns ratio in the transformer means a 63-86 Ohm resistor as the inrush limiter in the primary. It could be small like 220-300W with a delay between re-starts of 5-6 seconds, but in case of a failure where the soft start resistor is not disengaged then a 600W rating is minimum.

This brings up possible pulsing issues when the drive is turned on and off or varied widely, etc. but with the tube having a huge 225W grid there may be options. Audio rates don't look like an issue but jumps in level from cutoff to idling, and from idling to high power  could be.

Does anyone have experience with momentary excursions above the 3CX3000 rated plate voltage? The datasheet talks about pulse width modulation and 15KV, and this is why I want to study the Power Rock manual, to understand.

[KD6VXI]

I've run the 3cx3000A7 at 11.5 kv.   It would pump out 20kw plus,  pep.   This also used a bit higher filament voltage when keyed,  and slightly lower when unkeyed.  This was mobile,  with a couple three phase alternators.   I wouldn't suggest running it that way.......   BUT,  I don't think you'll have ANY problems with that spike.

The current incarnation has 4kv on the high tap of the xformer.   I've been able to run near 7.6kv, dropping to 7.2 keyed,  with no latent problems.

Hope this helps,  Pat.

--Shane
KD6VXI

[Opcom]

That's pretty encouraging. It does help, thanks for a direct account about this. Well 20KW might melt the copper off the copperweld. Heck, the 6-7KW that my little project might be capable of could endanger the OWL. But I'll be running the boring 1500W levels.

There are plenty of amplifier videos where the tube is run at overly high voltage according to a panel meter.
The swinging meters in some of those videos compete with the amp's builders for Guiness Book lying.

I believe the tube needs to be gettered after sitting 10+ years, before trying it. Somewhere on this board is a good topic on that. I should also finish my 4KW CCS dummy load. It's like the previous one, a bunch of chip resistors, microwave type, on a huge copper heat sink. Power supply first though.

Looks like all is clear to proceed on the power supply.  Unfortunately I am traveling from TX to CA in the company truck and the next two weekends won't have any activity. I will be getting some training on commercial UAV maintenance and operations. I may stop at Murphy's on 10/15 if time allows.

[KD6VXI]

Hmm.   Murphys,  UAV action...   Someone's going to San Diego!   Lol.   Make it up Bakersfield way,  lemme know.

I do not recommend running the tube that way at all.   It was just as a been there,  done that thing.   It was a 30 second burst,  so to speak.

Continental also marketed the power rock as another model,  I believe a 315-R1 rings a bell.

VE7RF has heat tested the 3 and 6000 tubes and found the diss ratings can be increased if you employ a chimney design that allows adequate airflow.   I believe he got a neat 50 pct increase on the 3cx6000, but I could be off.....   Been years since we talked about it.   Kind of like the yc156 being a 15000 tube with a 5000 radiator.


All about heat removal with the filament and grid the 3k and 6k have.   The CBers proved that.

--Shane
KD6VXI

[WA2SQQ]

I'm really impressed by this project- wish I was capable of doing this. So I have to ask - what is the projected completion date? I can't wait to hear it on the air.

[Opcom]

@KD6XVI I wish I had the time to do it and there are more surplus places in the area too, but since we announced our certification we already have many local people wanting to get their drones and UAVs serviced.

@WA2SQQ Thank you for saying so. I have many changing life-duties and no defined completion date. Maybe sometime next year. Basically the work is done about 4 hours a week. That may seem like a lot but it took 20 minutes to find and then about 2 hours to cut, paint, and install the insulating panel. Some things have to be made out of of other things and it's a job sometimes.

While in CA I visited Murphy's Surplus. The store has been re-organized and a visit is recommended. I had called him the week before and said I was visiting, asked about Saturday hours, etc. Fortunately I was able to get there on Friday later afternoon and avoid an extra hotel night, that is, I can't expect my boss to pay for my fiddlepharting around.
The traffic in CA was horrible as afternoon turned into rush hour. I spent over 3 hours doing 10-20MPH average. Imagine dropping your colleague off at the John Wayne airport at 1:30 PM, then being in that traffic and watching the precious hours of Murphy's business day tick tock away. I called and he said he would wait for me. That is what I call customer service!

I found some of these which I think are "finned strip heating element"s. Each measured 29-30 Ohms. Horrendous indestructible wattage I imagine. I bought three and there are several more. They are about 18-20" long. Price was just $5 each. The image is from a new one online. These are dirty and a bit oxidized from use but should clean up. They may be good for an indestructible inrush resistance. They may be 1KW size from an electric "HVAC furnace". The brand may be "wattco" or "hotwatt" http://www.hotwatt.com/stripmfgf.htm  and possibly on page 8 of this PDF: http://www.hotwatt.com/images/Web%20Page%20June%202010/Strip%20%20and%20Finned%20strip.pdf The bodies are stainless but the fins are steel and those are what really needs cleaned up.

I also picked up a partly cannibalized SONAR unit. 7" P7 CRT, magnetic deflection, the HV board seems intact but most of the other boards are gone. Its unusual in that it is a civilian or commercial unit and has a 360 degree display, a PPI display like a RADAR set. I think it could make a fine scope clock or something else, though it if were complete I had in mind an open air SONAR or a LIDAR.

Back to the amp, because the rectifiers are taking up room at the top on that side, the tuner probably won't fit there. I have a 19" panel with two CRTs in it and it may be worthwhile to consider a dual modulation scope, one the regular kind with sweep on the H axis and RF on the V axis, and the other set up for trapezoid where the incoming signal is detected to make audio, and that is plotted against RF. Alternately there is an HP 1300 type display or two around here. These are rack mountable 20MHz scopes with 9 to 11 inch rectangular CRTs. Lots of options.

The tuner should fit on the other side above the RF section. It all remains to be seen. If I am out of room I may have to relocate the solid state rectifiers. Wanting to include a high powered antenna matcher is one reason two racks were chosen.

[Opcom]

Amp stuff today.

As mentioned I procured three large heater elements from Murphy's in El Cajon, and a more suitable blower. The blower seems to make 1.25 inches of water pressure according to my home made manometer. I didn't have time yet to refill the nice one I got from Dennis that takes special fluid.

This is to say that the water in one column moved 1.25" when the blower was running as shown in the picture so I hope that's the way to measure it at 1.25". It has plenty if air volume available. I had to cut two small windows in the cardboard test block because when it was blocked off and not flowing any air the blower was stalling noisily and the pressure was varying. When delivering air it is nice and quiet. If there is no impediment to the air at all it 'overloads' that is the motor current goes way up. This is the first time I have witnessed and played with this phenomemon but it is mostly common on high performance blowers and very interesting. In the test it ran 2A. The nameplate says 7.6A and that would be with maximum air flow. The air flow will depend on the duct and what can be shoved through the tube. It's interesting that the pressure stays constant as the air flow is varied over the range of the blower. It would be boring old stuff to fan experts but it was interesting to play around with and see first hand.

[W7TFO]

That blower came from a Bauer 5kW AM TX.  It kept 2 4-1000's and a 4CX5,000 happy.

73DG

[Opcom]

The blower is perfect for this project. The use for the heaters is the inrush limiting. Some cleanup was needed due to a little rust on the fins and this could have been done with a wire brush but it was decided that with them in series for 90 Ohms total the fins could be removed and there would still be no danger of the units overheating if the soft start relay failed to close. The heater bodies are stainless steel. 240V across 90 Ohms is 640W or 213W for each unit. It's a lot of resistance but a very soft start is wanted to minimize the HV pulse toward the end of the capacitor charging. It should charge in about 200ms. If the pulse is not an issue these can be using in any combination of 30 Ohms each to speed things up.

[Opcom]

Removing the fins allows many more options for mounting. The fins are easily removed by grabbing the edge with a channel-lock pliers and twisting sharply so they break. The units can be supplied without fins and clamped to a vessel for surface heating, so in an extreme case they could be clamped to a rack for dissipation. This is not necessary here and they were mounted in a convenient way. The terminals are 3/4" from the side panel of the rack when it is installed. These giant heater units were just $5 each at Murphy's Surplus. There are a few more of these there at this time as well as some of other kinds and also some long quartz elements that would do a similar job. It beats paying big bucks for a resistors of similar specifications.

The last picture shows how much more room there is for the new single phase blower. It might be moved to the other side to be under the RF section and the large filter cap moved where the blower is now shown.

[Opcom]

First the text, what was done and why, then some pictures from Sunday.

Last weekend no images were taken. Despite some sort of evolving diagram, the soft start resistors were put across the wrong mercury contactor. This kind of thing happens when something is left along for a week at a time. It took a couple hours to redo that wiring.

Jacob made up a house-type 120VAC receptacle with mounting plate and ran some wire there for the blower motor. We thought it would be best to use a receptacle and plug for the blower so that if it ever needs service, it can just be unplugged and removed rather than having to unsolder or unscrew wire terminals while crouching low to the floor. I don't do that very well any more. The 'extra' side of the receptacle can feed other cabinet cooling fan(s) and or disco lights to be determined.

Today some difficult decisions were made resulting in a big time-out for planning and measuring. The result of that was a major and probably final  re-arrangement of components. This was on top of finally connecting the two 'floor' planks on each side together with stout "L" iron and mounting the plate transformer. The final result is that next weekend, barring problems, we can start running the high voltage wiring.

The solid state rectifiers were removed from the inconvenient location at the top rear of the right cabinet and moved to the lower front of the left cabinet. The space at the top of the right cabinet was re-claimed for whatever lofty purpose. Meters, tuner, scope, whatever ends up there after the RF section is built.

The blower was moved from the the left cabinet to the right cabinet and mounted with the scroll case facing forward. A thickness of sound absorbing material to be determined should be put on the backside of the lower right rack panel, and a cone or some other air-turning device put in front of the blower. This may eliminate some of the blower noise as long as the blower is not too close to the panel. There is a convenient path from its output for a flexible duct to the left cabinet and vaguely planned RF chassis location.

The filter capacitor was moved to the front of the right cabinet and sits front-to-back beside the blower.

The filter choke now sits at the back of the right cabinet. An insulating device has to be made later to prevent acidents in case the electronic brain has to be troubleshot with the unit on, but I am thinking about a set of lights to indicate the status of the controls so that troubleshooting is made simpler.

A piece of 1.5" "L" iron is screwed into the floor planks on the right side at the front. This connects the 'floor' planks on the right side together to make them stay level with each other (another at the back will be added) and this front "L" may have to also support the front rack panel because there are no rack rails at the bottom of the right cabinet. The cabinetry is an AMCO modular enclosure and is now their legacy or FX line of Electronic Packaging enclosures, so some rails may be able to be had. The "MXL mounting channels" look like the right thing. The fact that this is still made today says it is a timless design.

There is enough room next to the solid state rectifiers for a bleeder stack. There just happens to be an insulating board with ten 100K 100W resistors on it from a cannibalized 13KV 2A regulated power supply. These are Ohmite and their spec is that the unit will take the voltage required for its rated dissipation. In a 100K 100W resistor this would be 31mA and 3162V. The resistors are designed for convection cooling but maybe a fan will be used to remove heat from the area and increase the safety margin.

Possible bleeder resistances using the board with good safety margins are 250K@20mA, 100K@50mA, 50K@100mA, 40K@125mA.

Bleeders : HV @ bleeder load
250K: 6620V@20mA 132W, 13W per R (10 pcs)
100K: 6021V@60mA 361W, 40W per R (9 pcs.)
50K: 5400V@108mA 583W, 72W per R (8 pcs.)
40K: 5188V@129mA 669W, 70W per R (10 pcs)

Normally the RF tube's idling current will hold the power suply in its good regulation area. There's a balance to be struck between the danger that the tube may not light or work, causing the voltage to increase too much, and the wasting of hundreds of Watts in the bleeder. A bleeder has to be there but maybe there is a way to detect a tube-not-running condition and shut off the HV. That would avoid a 500W+ bleeder. (That said the Tucker TX only makes 700W carrier/2800W PEP and it has 200mA of bleeders; 680W!! Big bleeders: not 'fraid of 'em)



If anyone wants the 3 phase plate transformer from the previously mentioned cannibalized power supply let me know. I don't know the primary or secondary voltages but the connection was fullwave bridge of 18 Varo VC80 8KV 1A rectifiers (3 per leg) with a 1uF capacitor. It's in a 4 FT rack with wheels (some undisclosed low-value parts still in there too) in Gainesville TX. This means it's cheap if someone wants to pick it up by appointment only.

[Opcom]

Rear view of right cabinet. Choke is at the back, cap and blower up front. An L bracket still needs put in back here to connect the 2x12 floor boards so they are flat and level. Recall that they are supported only at the rack's 4 corners so a heavy weight makes them tilt down in the middle rather than act as one piece. When this was done on the other side with the plate transformer, the boards could be seen being drawn up level as the lag bolts were tightened. Each "L" bracket has six lag bolts 1.5" long. Holes about the same size as the lag bolts shaft diameter of 0.205" (not the ~0.25" thread diameter) were pre-drilled. I think a 7/32" (0.21875") drill was used and a 3/16 (0.1875") might have been too small, concerned with splitting the wood maybe.

Rear view of left cabinet. Silicon rectifiers mounted up front. They are 3u above the rack floor. The thumbscrews, remember are how the HV wire attaches and this has to be made easy to work on because it may need service at some future time. The bleeder unit is just standing there next to the rectifiers. It should mount up to the inside of the rack and already has standoff insulators. At the very top of the bleeder board is already a HV resistor of 20 meg. It probably went to the regulator error amp in the power supply the bleeder assembly came from. The plate transformer sits on the two "L" brackets in this side of the rack. Its weight alone made the floor straighten up but it needed mounting. The brackets were fastened to the floor with lag bolts. The transformer is held to the "L" brackets by 3/8-24 grade 8 bolts. I do not claim it will stay there if the cabinet is turned upside down but it isn't going anywhere in normal situations. There was a long and complicated procedure to do this "L" bracket and mounting job without taking the transformer back out of the cabinet. It's too tedious to describe here.

Front view of left cabinet. The space can be covered by a panel. The plate transformer is taller than the space taken by the silicon rectifiers and bleeders. The rack floor space seems very efficiently used, yet everything can be gotten to, and nameplates seen for those who like to read them. It may seem like a lot of extra HV wire would be needed to have the silicon diodes here and the mercury diodes up front but since each silicon diode stack is in series with one mercury rectifier, and the choke and filter are both close by, it only adds a few feet to the whole. An "L" bracket can be seen in the right side cabinet.

[Opcom]

A view of the nice receptacle Jacob made up. The plug and green twisted pair go to the blower motor. The messy power cable hookup will eventually be relocated after the power supply is completely done.

Reclaimed space in the top of the left cabinet.

[Opcom]

A possible improvement might be to rotate the silicon rectifier assy. 180 degrees so that the stacks are to the left. The extra space for the bleeder unit will then be on the right and a small amount of air from the blower can be directed at the bleeders. The hacked up picture shows the idea.

It is not too hard to make little nozzles or vanes from cardboard stiffened with epoxy or from plastic softened and bent with a heat gun or to use a fiberglass repair kit in some way.  The drawing shows the idea.  It does not have to be elaborate or expensive. . I have done this kind of thing in racks before where a single blower fed a cardboard duct and it ran down the backside of the rack with little cut out windows in it, the flaps of the windows aimed the air at the receivers and how open or closed they were determined how much air each got, so the ones at the far end got as much as the ones near the blower.

Sorry if this is tedious but these small details may help prevent heat damage over the long term. The resistors could use convection but the board they are on is subject to be being heated.
After seeing how the circuit boards in some old broadcast transmitters are brown and cooked just like the board in a cheap TV set, there's no excuse for that.

[Opcom]

Most of the power supply HV wire was done today. Not quite ready for test.

The HV circuit wire was run in two PVC tubes because there is low voltage wiring in the center section. Its 15KV GTO #14. Rectifiers and bleeder board all mounted.

[Opcom]

Different colored wire ties are put on the HV wires so to identify each end of the same wire.

The bleeder board is on 3" standoffs and the resistors are at least 1" from the metal of the rack. The resistors face the area where the blower goes. Right now, 9 resistors are used, each 100K 100W in a 3x3 arrangement.

[Opcom]

There is also a mess here from this project.

[KE5YTV]

Pat,
I'm very impressed with your amp. I wish I had the knowledge and parts supply to visualize that project and just start putting it together. Good job! Bye the way, your work area looks like mine. I would feel at home there. 

Mike
KE5YTV

[Opcom]

Thank you Mike. The parts have been collecting for a long time. It's not so different from any amp in the handbooks except the size. Just some thing I always wanted to try.

Today is momentous because the power supply was tested. A 0-10KV HV meter was temporarily made for testing using a couple of 100M HV resistors and an old 50uA meter.

The MV rectifier filament delay and soft start worked great.

The cap has 3/8" terminals. There were no ring connectors that size so some adapters were made of pieces of plated steel strap so 1/4" hardware could be used.

[Opcom]

The HV was 6200V max. with the 100K bleeder

[W3RSW]

"Leakage current" 
That's a good one.