Gain? Oh I love their detergent.

The hardest part of having false hope is when it all falls apart. Here, I’d been told that the PowerCD transmitter that I lovingly call the Space Station Toilet was going to be replaced starting in April or so.

Oops. Turns out nobody has any of the required supplies for that project in stock anywhere and production isn’t expected until July at least with an estimate on replacement being maaaaaybe September… and every tiny setback adds another fortnight of business days to the backlog. Time to start making this thing as happy as possible to prolong its final year (or decade?) of service…

Another adventure at the Space Station Restroom standing tall in a field by the river… This is cabinet #1 of 3. Cabinet 3 was the one that gave me such elegant fits before when I did a grid scrub. Cab 1 wasn’t causing as much drama but it just wasn’t making enough power prior to the scrub and was occasionally arcing out, roughly once a day. Let’s gooooooo to the wash!

π amps
As it fights me, the usual

Yes, of course it keeps trying to flip back to BG Heat every few minutes so you just have to stand there in front of it and pwap the standby button each time. Annoying. I thought about just raising the filament voltage in BG Heat but realized that’d be a terrible idea as the cooling system shuts down when you’re in BG Heat! I can’t remember if the air blower eventually goes down, but the water pump definitely does.

As I prepared to do the grid scrub (which requires hooking up an external power supply to the ESCIOT tube grid and cathode), I went into the high voltage cabinet with some isopropanol and blue shop towels and did a, well, scrub.

The long blue voltage divider resistors in between the insulators on those weird terminals were pretty mucky.
My unspoken rule: always say “boop!” each time you touch something with the discharge stick. This helps me get over the slight fear that something is going to go SNAP! due to residual charge.

What’s that now? Oily sticky gook…. just like I found in the other cabinet? Hmm. I’m beginning to wonder if this is ethylene glycol that’s been electrostatically precipitated out of the air, since this rig is known to absolutely REEK of Dowtherm SR-1. The recirculating pump/reservoir unit is far from airtight so it just outgasses.

And now, Deja Moo: the feeling I’ve seen this BS before—

Yes, again with the weird scunge fractal on the +3.5KV ion pump supply

Look at the upper left: this robot has seen some shit, man

He likes it! Hey Mikey!

Amazingly I did not find it necessary to readjust the grid voltage after the scrub, it just… Worked. I was not expecting this. Not out of this turdly transmitter.

Then came the surprise. I was walking past checking the coolant system pressure on the pumps for the other transmitter in the room (a rather boring solid state ULXT-80) when I saw one of its variable frequency drives blinking “OCL”. Interesting. I first foolishly decided to take the cooling fan cover on the TEFC pump motor off, thinking I was going to find a seized pump. I spun the fan and found no unusual resistance. Upon opening the cover over the drives I was greeted by….. toast.

Not sure what went first, the screw terminal or the crimp forked terminal that was stuck in it, but something got hot until it cratered the poor drive. Ow! And to make matters more fun, as is always the case nowadays…. nobody seems to have these drives in stock anymore. Luckily, GatesAir has them, for about the same price as a better quality Fuji Electric drive from Grainger. Hmm. Do I…? I’ll have to make sure the Fuji has the right I/O first before doing anything that daring. On a side note, if GatesAir is going to charge that much for a drive they marked up like 100% they could at least take it out of the box and program it for you. They do not do this.

Then again this is the same manufacturer that charged us about $500 for four small rubber washers that I strongly suspect were just pieces of EPDM rubber hose cut carefully to length.


It’s my personal opinion that these Toshiba drives are built like damn toilet paper. They were only common in everything because they’re cheap and have tons of I/O options. Bad power will murder them in no time. It didn’t even get a chance on this one as thermal runway at the terminals Popped It.

Well then, all that resolved, it was time for the last silly task of the day: go see why the surveillance camera up top was giving us no usable image….


Yeah, uh… That’ll do it.

For the want of a blue shop towel and some isopropanol

It’s done. It’s working. It’s……. perplexing as hell……

And I think it was just merely DIRTY!!!

So I was working on the Space Station Toilet again today. Over the past few days I had been gradually baby stepping it back up to normal output power from zero, and today after several crowbar dumps I almost entirely gave up on it before deciding…. hey, maybe that isn’t the tube, but something else. Something externally… arcy sparky? Anyway..

You’ll get your wattage…. IN HELL!

The first thing I decided to look at was the grid voltage setting. This is described in very short in the manual – you want to hook up a spectrum analyzer and adjust the grid voltage first so that you have less than 800mA cathode current with no drive, but then so you have the best possible shoulder attenuation without excessive cathode current once you have applied drive. In theory, it sounds like you should basically have a sweet spot in between the two. In practice…. I found that varying the grid voltage one step at a time allowed me to find a narrow peak. On one side I had excessively tall shoulders like some kinda wild vintage dress from the 80s, on the other side, the shoulders would abruptly pop back up accompanied by the amp faulting out on high collector current on collector #3 or #4, but without the cathode current being all that high compared to that on the other amps. Weird but, uh, ok.

Here’s a mostly passable reading

So once I had the grid peaked up nicely, I decided to try running more power. I got to 100% of normal output and it was stable! Then I walked away and walked past the cabinet again and *BANG* *thump* *gronk* *screech* everything crapped out. It crowbarred and took down the whole UPS and caused the other two cabinets to stop and restart. A real fucko boingo, as they say UwU.

I tried bringing it back with the drive off. It thumped twice at the end of the quiescent verify stage and oopsie poopsied everything again dumping out its beamy weamy.

After about three cycles of not even being able to get into beam on with drive inhibited, I got very frustrated thinking the tube might have been damaged and kicked the cabinet. Now I was able to get into beam on again. Hmmmm…. Time to look around a bit. I shut off and grounded the rig for a look around. Now, this isn’t a picture of the same exact cabinet so you won’t see what I found but I’ll describe it…

The big silver suitcase looking thing is the “ISO Power Supply”. It is mounted on big insulating rails that look like they’re made of FR4 material or something similar. I was inspecting the high voltage leads above that go to the tube when my coworker and I noticed big oily sticky patches on both sides of the ISO supply case.

There was no apparent source for any oily substance to have dripped down onto the supply, so I pulled it out and opened it just in case I was missing something weird like a leaky oil filled cap that managed to get junk everywhere. The black plastic latch releases and it opens like a briefcase… Here’s what it looks like on a spare unit we have.

Left side — Top left: grid bias supply (up to about -300vdc, up to 50mA or so). Top right: filament supply (variable to at least 6.5v, uh– 20 amps?). Right side — left: ion pump power supply (-3.5kv, few microamps). Right: microcontroller with optical canbus I/O.

Well, on this one, something jumped out at me right away, and with that, the light came on.


The arc tracked layer of filth came off with a little careful cleaning. Where it was located, it would have been arcing right near the logic side of the grid voltage supply, perhaps glitching it out. Now, one of the things that varying the grid voltage does is to cause the cathode current to change.

The way the transmitter detects a damaging arc inside the eev ESCIOT inductive output tube is by looking for sudden noisy jumps in the cathode current. The supply wire runs through this big toroidal transformer on the “Spark Gap Interface” card.

I took this weird closeup because I was amused at “TOROID BOAT”

The white object that looks like a big bottle stopper is a triggered spark gap tube. There are no power or signal connections to this card. All it does is if the current on the wire looped through the transformer at left, it rectifies the resulting ac current to DC, and uses the transistor hidden partially under the wire here to pulse the primary winding of the black trigger coil. This causes the spark gap unit to arc over, abruptly forcing the beam supply to ground and causing an ugly high current fault…. but protecting the tube from damage.

And what else could have been making the beam current dance and fire the spark gap? Yeah— a glitchy grid supply which would make the transconductance of the tube do the fandango.

And now the ridiculous beast is tame, running full power, big wattage, no whammies.

73’s and good night

¡Atencion! Esto es un post de mierda.

Yeah so now I know why nobody ever does the grid scrub / ESCIOT outgassing procedure on this thing– it makes it nigh fucking impossible

Yeah sure just leave it in standby while ramping up the grid voltage aaaaaand I’m just going to keep repeatedly kicking out into BG Heat and reducing the filament voltage to make your life interesting.


So yeah after I managed to get the dumb thing through the grid scrub and tried to put it back on air I experienced a very loud and through “oops I’m crowbarring and taking the whole plant down with me as I go” incident due to an arc in the tube at just 8 kilowatts output, it really isn’t ready to go back to work and is being a spicy little electron box.

I’m going home and hiding myself under this cat


Me: “how could the Space Station Toilet  need a new flow meter on the HPA 2 collector loop after less than a year?”

The Space Station Toilet: “hahaha MONCH, have fun with this!”

The ceramic shaft was completely cut through on one side and visibly contaminated by metal debris on the other, likely from the tube body cooler.

What am I going to use as the subject of angry hissing on this blog after the Space Station Toilet gets replaced with a boring new rig in April or so??


Evertz what did you do

Ok let’s just go in here and replace these bad power supplies

Hmm, weird….. There are three different sets of CPUs and RAM in there!

DDR3(?) ECC ram, makes sense
Hold up is that. Is that DDR1?! There’s some other bga mounted ram peeking out to the left of that roundboi cooler.

what. WHAT. It left the factory like that. It passed “QUALITY” CONTROL. What.

But somehow it works. Thanks I hate it.

You know what? I never want to see this again and maybe they were doing us a favor by using those crappy screws on the top cover where you have to drill out one or two because they’re galled and the head is made of pure nacho cheeze.



FOUR LEAKS THIS TIME! Cha-cha real smooth.


Take it back now y’all.

With the assistance of Jack Davis (Jackpot Engineering), we got in there and changed out the tube body cooler ring, and the whole thing lived to tell about it…

I didn’t get pictures of the process because my hands were two of the six hoisting parts on and off of the thing, but here was the process:
Remove tube cart, place under chain hoist.
Pluck out tube.
Unbolt input cavity/socket assembly from below, drop it down and remove.
Remove bolts holding secondary cavity to cart legs and remove screws from underneath that hold those four round black vertical standoffs to the top plate of the cart. Hoist the top of the cart up a few inches.
Unbolt and remove grid ring cooler.
Admire the corroded mess.

Korrosion Krispies.

This looks as if water may have been slowly getting out INSIDE the ring in addition to the externally visible leaks down on the lines feeding it, it was DONE. Please note the heavy coating of black silver oxide. This continued to make itself known throughout the procedure.

This was leak #1 down…….

“Does anyone know the last time the ceramics of the tube were cleaned?”
*dead silence*



So, good cleaning of the tube is vital as there’s a BIG voltage gradient across the large white ceramic cylinder, as well as between the filament (innermost two rings) and the next ring up, assuming that’s the ion pump (3.5 KV!)….


I didn’t even realize the very bottom there had a ridged porcelain bushing around it – it looked to me like some kind of dull finish aluminum alloy piece from all the mess stuck on it.

Note the spot where I wiped it with my finger which came away black. I guess this also illustrates where all the air gets sucked out at time of manufacturing – it’s got a center exhaust like a light bulb!

After scrubdown:

Well mostly.

The unglazed part of the bushing appears to just be permanently stained. I even tried Scotch-Brite pads on it. The glazed outside cleaned up perfectly.

And now, time for some massive, ugly cleaning.

Ever had a faux leather case on something or a piece of clothing where the outermost texturized layer of the material started shedding, forming an evil sticky glitter-like flaky substance that sticks to everything and spreads everywhere like the DISEASE of craft supplies itself?! Yeah— imagine that, but made of silver oxide, CONDUCTIVE, and coating most surfaces of the output cavities. Gee, no wonder I was getting cavity arcs in the log every day or so. YAAACK.

Brush, vacuum, brush, vacuum, bleeech.

Finally it was time to put it all back together, at which time I experienced leak number 2 — one of the Hansen couplers blew its o-ring and started spraying water down the back of the tube cart. These things work just like pneumatic line couplers you may be familiar with from air tools, just, big and angry and stuff. You can’t see it well at this angle but there’s a hard nylon ring up inside there followed by a rubber gasket. The rubber gasket had ceased to be, just like any of the Barnstead filter gaskets every time you look at them wrong.

So I left the amplifier running into the combiner load overnight, came back the next day and found a nice puddle of red splooey on the floor below the external glycol piping behind the cabinets. LEAK #3!!!

The source was the mid-body seal of a ball valve that literally would never have been touched since the day the transmitter cooling system was filled up and made ready for the rig to go on air. It’s a valve that’d let you bypass the outdoor heat exchangers and just circulate the Dowtherm glycol solution through the pump/tank unit and the amplifier cabinets. I’ve never seen a ball valve fail this way before. have you? Probably not. IT’S JUST POWERFULLY CURSED OK


Finally, Leak #4 happened on some of the blue hoses at the Barnstead filters, I was so done with this thing I didn’t take a picture, just cut the hose a little shorter and smashed it back onto the fittings, BYESIES

So that’s the tale of FOUR LEAKS on the Harris PisserCD.

Stay tuned for when I attempt a grid scrub / outgassing procedure on this stupid thing which has been last performed probably about when the tube ceramics were last cleaned, which is to say, oh, half a decade ago. -29mA grid current? Ok yeah sure thanks for that. What else is even left on this thing to leak??

A quick look at the GatesAir UHF TV transmitter

This one is shaped like a big rectangular friend. It’s a GatesAir ULXTE-30, which can give you 19.2 kilowatts out of its 30 amplifier modules.

This one’s practically brand new and is pretty much an illustration of how densely you can build a LDMOS based solid state linear amplifier! Gates says it can give you up to 45% efficiency which is pretty dang good for linear amplification – a necessary evil with transmission modes that use amplitude keying such as 8VSB, QAM, and COFDM. All the major heat sources on this unit are cooled by a standard 50% mix automotive grade antifreeze solution circulated through tubes in the modules.

From top to bottom:

I forgot to annotate this but the harmonic filter is that ridged black tube up top above the cabinet. It doesn’t get dissipate much energy at all and requires no active cooling.

The exciters are responsible for generating the RF carrier, modulating it with data input from the broadcast encoders (back at the studio in our case), and applying precorrection for frequency and group delay response of the amplifier and filter system. GatesAir calls the latter their RTAC System, for Real-time Active Correction. Only one is actually on air at a time, but you can switch exciter in case of one failing, or to allow you to do things like update the software on one while the other is on air.

The controller provides local and remote (web interface) control and metering of the transmitter’s functioning as well as controlling the power and cooling systems. It has canbus communications to the rest of the system.

You can see that the modules below are in three distinct groups. This is because the whole thing is of a modular design; lower wattage units may have only one or two of those ten-pack units and can even have the cooling pump station built right into the bottom of the cabinet! This one’s just packed with power, though. The power supplies are slide out modules with air cooling – they’re pretty high efficiency so they don’t need a lot of airflow. The weird little pick on the door is used to lift the latch that holds them in if you have to remove one.

In each group of modules, the upper two are a preamp and driver stage, and the rest are final power amplifiers. The output of each goes to a backplane with a combiner that feeds into the large black combiner seen in the back of the cabinet. The two glycol cooled reject loads absorb any reflected power caused by imbalances in the system.

Look carefully and you’ll see I placed a pink asterisk at the top. This is indicating a small yellow wifi router. If you don’t use this I’d recommend unplugging the power lead to it. It’s not vital for anything, it’s basically just used if you have a wireless tablet used to get into the web interface instead of a device on wired Ethernet.

The pumps are external on this system. They’re the unit on the right here. To the left is a combiner and filter unit that’s combining this and the output of another transmitter to a common transmission line and antenna. There are four variable frequency drives on it, two control the pumps and two control the fans outside on the radiator.

The heat yeeter:

To date the only thing I’ve had to do with this transmitter was replace one power supply module that tanked under warranty and top up the cooling system. It’s a good tall beige friend.

What’s in a module, as pictured in the brochure.