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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Sun 29, 2020 1:50 am 
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Location: Santa Rosa, CA
Thanks to all that have posted info and pics. Keep it coming! A very
interesting subject.

Some of the technical details are also fascinating. Discovered, in at least the
RCA TT-5 series, (5 KW) the transmitter generates supressed carrier DSB
then uses a *water cooled* coax filter to filter out most of the unwanted
sideband.

Congrats to the guys that have managed to get some of the tubes and bits
from these old work horses. It doesn't seem like many survived which is
unfortunate.
Steve

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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Sun 29, 2020 2:22 am 
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The workhorse tube for most of these transmitters was the 6166. Here is a link to a data sheet for this monster:

https://frank.pocnet.net/sheets/049/6/6166.pdf

Some salient numbers:

Directly heated thoriated tungsten filament, 5 volts, 181 amps (yes you read it right!)

Max plate volts 6000
Max plate current 10 amps.

In this early 60's AWA Australia corporate film you will see what looks like a 6166 being made, starting about 7 mins in. (Don't worry about the shredded VHS tape at the start of the film, it gets better!). I was surprised AWA actually made 6166s in Oz. Also some good footage of CRTs being made. And early transistors.

Strange to see the US Indian Head test card being used in the factory, we never saw it anywhere on TV here. Usually the Marconi resolution chart.

Oh, and here's a shot of the transmitting site I mentioned. Taken from the Pacific Hwy, thanks to Streetview.

Attachment:
Mowbray Rd site.png
Mowbray Rd site.png [ 734.69 KiB | Viewed 590 times ]


Interesting to note that the tower no longer carries ID for ATN 7 and TEN 10 who were the first to use it. Used to be on link dishes facing the highway. Looking around the site today, there is no signage clue as to what it does.

Sydney is in the grip of an infrastructure building boom. Nearby a new underground metro I suspect tunnels right under this site to augment the main heavy rail commuter lines just beyond the tower.



https://www.youtube.com/watch?v=89pNkNIAcI4

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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Sun 29, 2020 3:06 am 
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Location: Belrose, NSW, Australia
Quote:
Some of the technical details are also fascinating. Discovered, in at least the
RCA TT-5 series, (5 KW) the transmitter generates supressed carrier DSB
then uses a *water cooled* coax filter to filter out most of the unwanted
sideband.


Yes that is one of the big problems with high level modulated transmitters, not just the TT-5, all that power in the unwanted sideband has to be got rid of before it goes up the tower. However, with other methods there were efficiency tradeoffs too.

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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Sun 29, 2020 5:52 pm 
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After researching a little, I see that the transmitter I posted from Switzerland (RCA TTU-1B) is a 1000 watt UHF transmitter. I wonder if my information about this being the first TV transmitter in Switzerland is correct? I'm surprised their first would have been UHF.

It's interesting to read through this RCA catalog of TV transmitters: https://www.americanradiohistory.com/Ar ... g-1956.pdf

I didn't realize that some TV stations apparently used rather low power from the transmitters, in the low kW range. I guess with the right antenna to compress the radiation into horizontal lobes, the effective radiated power could be significantly higher, but I admit I expected to see higher numbers. RCA did make larger ones, up to 100 kW, but I wonder what the distribution of power levels was? Some of you probably know.

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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Sun 29, 2020 9:36 pm 
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I'm pretty sure that over 1 megawatts of Effective Radiated Power (ERP) was achieved in the early 1970s, with the RCA TTU-110 (110 KW) and the appropriate gain antenna. The TTU-110 was created by paralleling two TTU-55 transmitters through a combiner (directional coupler). The combiner's load had to be ready to handle the transmitter output if something happened, so it was a huge water-cooled thing, as someone else noted. Made by Bird, of RF wattmeter fame. Incredibly noisy cooling system -- essentially a very big air conditioner.

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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Sun 29, 2020 11:30 pm 
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Thinking about these old transmitters, I have been going crazy trying to recall the antenna impedance of the RCA TT-5 transmitter. If I recall correctly the later transmitters were 51.5 ohms, but 50 ohms or 70 ohms sticks in my brain. Jim T., I hope you see this and can recall.


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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Mon 30, 2020 6:11 am 
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Greetings to J. Hill and the Forum:

Actually, 50 ohms is the late comer. The way I heard it was this:

In the good old days immediately following WW II when the TV boom first got started, it was necessary to come up with some high power transmission lines. However, no one was really set up to make copper pipe of custom dimensions. So, they picked some plumbing pipe off the shelf and this was 3 1/8" diameter (inside diameter, I think but it's been too long) and that was a good size for the outer conductor. Unfortunately, the closest standard copper water pipe size to fit inside the big pipe and get close to 50 ohms didn't make 50 ohms, it made 51.5 ohms as the characteristic impedance. So, 51.5 ohms became a standard. Eventually, people started tooling up to make inner conductor in the correct size for 50 ohms and that became the new standard and the 51.5 ohm stuff became more or less history.

Warning: Anecdote to follow!

I once had to shift some 3 1/8" transmission line around to accommodate a new coaxial switch that was being installed for KNX-FM. This was shortly after I went to work for CBS... and I didn't know the tale of 50 versus 51.5 ohm transmission line. The connection I had to make was to the output pipe on a Collins 830 10 KW FM broadcast transmitter. I dully got the lengths right and bolted everything down. I then went to tune up the Collins and boy, did it act squirrely. I couldn't seem to get any real power out, the coupling was way out in left field... what was going on?!

The boss came to the rescue. He asked me if I had used a "whisky cup". I said something intelligent and articulate like "Huh?" He then proceeded to tell me about the difference in transmission line standards... and that the Collins 830 was built in the 51.5 ohm era. The 51.5 ohm center conductor is slightly smaller than the 50 ohm center conductor, so there was no actual connection between the two. Instead, there was a very small value series capacitor formed by the slight protrusion of the Collins 51.5 ohm stub into the 50 ohm pipe. This capacitor was too small in value to do the job of matching the line impedances, so the results were less than optimal.

A "whiskey cup" is a gadget about the same size and shape as a real whisky cup except with thinner and silver plated spring contact walls. This is slipped over the 51.5 ohm center conductor and provides a good electrical connection to the inner wall of a 50 ohm center conductor.

After correcting my little faux pas, I was able to tune up the transmitter with no difficulty.

Regarding 75 ohm line, the higher Z line has less loss and is therefore preferred for UHF installations, where is where you will mostly find it.

Regarding the TT-5, I doubt that you will find it to be a DSB suppressed carrier transmitter. NTSC TV is an AM system requiring a full carrier for detection. The lower sideband is truncated to "vestigial sideband" to save bandwidth while preserving accurate demodulation at low frequencies. The carrier and upper sideband are as normal in an AM system. The TT-5 is a very interesting piece of technology. It uses grid modulation of the PA... requiring 600 volts of nice, linear undistorted video with a bandwidth of 4.5 MHz. Let's see you design an amplifier that can deliver that!

The aural side FM transmitter used a mechanical servo system for frequency control. One might think it primitive, except that I might point out that most TT-5 transmitters were working fine when removed from service... many years after their installation.

I think that most TT-5 transmitters were converted to use an air-cooled final later in life, which simplified the installation considerably. For the original tube, water cooling was a must... this was a 5 KW AM transmitter... and that power was being routed through two plates (anodes) each the size of a postage stamp and together in one envelope. Needless to say, they were hollow copper blocks through which cooling water circulated.

I got to watch the TT-5 that belonged to KHJ-TV being pulled from service. It was sold to a mom-and-pop station that was going to set it up in (as I recall) Tonopah, Nevada. It wasn't too long after that that HDTV started coming on the scene and the TT-5 can't do digital so it would be useless. So... if you want to be a relic hunter, head for Tonopah and see if you can find it. :D

That's where I learned about what an amazing piece of technology for its time it actually was.

BTW, when I left Mt. Wilson about 2011, KNBC still had their TT-5 system installed. I don't know if it's still there or not, but it might be... it sort of made up most of the interior walls of the building... and for all I know, it might have held up the roof as well! :D

Regards,

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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Mon 30, 2020 7:56 pm 
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Jim T. You are correct that the TT-5 was 51.5 ohm. I found a copy of the instruction book on the internet which confirms this. I thought and was able to confirm that the mid 1950's TT-50A was also also 51.5. We had a TT-2A backup transmitter hooked to the antenna left over from the TT-5 and as I recall the impedance of the antenna was not the same as the TT-2A. It seems that the TT-2A was something quite a bit different, but it has been a lot of years.
You saw the TT-5 leave KHJ (KCAL), I was working there at that time. I was very sad to see it go. I was told that it never was put in service in Nevada, but ended up in a junk pile in the back of a gas station.
The TT-2A was not at Kcal, but up he street at KCOP, where I spent the majority of my television time.
It appears we worked at Mt. Wilson at about the same time, only you were at CBS and I was at poverty row!
Jim


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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Mon 30, 2020 8:38 pm 
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Greetings to J. Hill and the Forum:

It looks as though I'm hi-jacking this thread, but you must have known Frank Grill if you worked for KCAL/ KHJ. A real gentleman and most knowledgeable. He is missed.

BTW, when CBS bought KCAL, we consolidated a lot of test equipment. We got rid of a lot of stuff, and the boss told us to take it if we wanted it. I happen to have an HP 141T and some plug-ins for it with RKO property tags still stuck on. :D

That shows how old the stuff was... that was before Young Broadcasting and then Disney! I think it was Young Broadcasting, wasn't it? Anyway, none of the later owners cared enough about a non-functional 141-T to update the property tags.

Regards,

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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Mon 30, 2020 8:58 pm 
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Yes indeed I knew Frank. He is the one who got the 8D21 for me. He thought it was appropriate because that tube started life at KCOP and then went to KHJ, as I did! Did you notice the old file cabinet up there that has the property tag from RKO Pathe? When did you start on the mountain? I bounced back and forth studio transmitter at KCOP from 1968 to mid 1970's when I ended up almost exclusively on mountain. I went to KHJ in about 1981 and left television in 1989. Did you know Jim Sampley, Jack Franklin or Ken Gearhart


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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Mon 30, 2020 9:23 pm 
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Greetings to J. Hill and the Forum:

I started in August of 1981 and got transferred to the studio in 2011. Retired in 2013. Sorry, I do not know any of the other gentlemen. I did know Doug Sabe (sp?) who was the KCAL transmitter guy when we bought them from Disney.

Regards,

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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Mon 30, 2020 9:32 pm 
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The NBC affiliate in Pittsburgh, WPXI (formerly known as WIIC) was still using their original 1957 rig as a backup in the mid 1980s; I think that it was an RCA.

At the same time, WTOV (formerly known as WSTV) in Steubenville, Ohio still had their original GE transmitter, which was probably even older.

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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Tue 31, 2020 4:33 pm 
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There are many old UHF transmitters operating and using lots of expensive electricity.

UHF transmitters using Inductive Output Tubes could be converted to ATSC3.0. Many of these transmitters were designed as analog and then changed to ATSC1.0 (current Digital Standard).

The ATSC3.0 transmitters currently on the air were made to ATSC1.0 but upgraded to 3.0 with a few simple adjustments and a new Modulator (Called Exciter by some)

Analog TV operating on UHF bands would typically run 5 Megawatts ERP which required 5 Klystron Tubes which were less than 40% efficient.

During the 1990's the Inductive Output Tube came on the scene and this tube gets above 40% efficient These transmitters were made to be converted to digital. Many are still running on their third generation of updated modulator.

The Tube transmitters require liquid cooling (antifreeze). and suck down a lot of electricity.

The All Solidstate transmitters are liquid cooled for the most part and instead of two or three tubes they now have a couple of thousand Field Effect Transistors and Strip=Line power combining networks.

Jim


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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Tue 31, 2020 10:09 pm 
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Greetings to jimmc and the Forum:

I think I'd like to post some qualifiers to what you have written.

Any UHF transmitter that starts with a low level signal and amplifies it with linear following stages can do ATSC... any version, so long as it fits in the 6 MHz original channel bandwidth. All that is necessary is an appropriate exciter change. Very few, if any, broadcasters would want to convert a transmitter using klystrons to HDTV because of the power inefficiency. True klystrons run class A and are about 25% efficient, if that.

The IOT, or Inductive Output Tube, is basically a gridded klystron with a single output cavity. I've changed out a number of them in my career, specifically the IOT-D2100B from EEV/Marconi.

Attachment:
e2v_0623.jpg
e2v_0623.jpg [ 61.22 KiB | Viewed 476 times ]


These tubes can achieve 40% efficiency, but that's about it. Again, since almost everything concerning the type of emission is determined by the exciter, they can run any version of ATSC that fits in the 6 MHz channel bandwidth.

The last solid-state UHF transmitter that I dealt with before retiring from CBS was the Harris Diamond series. It is air-cooled.

Solid-state analog TV transmitters were typically made up of numerous FETs, combined with Wilkinson strip-line combiners. Again, air cooled for the most part. Here's a module out of the Larcan transmitters used by KCBS on channel 2.

Attachment:
Larcan PA Module.jpg
Larcan PA Module.jpg [ 367.38 KiB | Viewed 476 times ]


The Harris Platinum solid-state transmitter that was the KCAL channel 9 analog transmitter was converted to ATSC 1 without difficulty and as far as I know is still their main transmitter. It is also air cooled.

I understand the latest trend is to liquid cooling because of power density factors and because it simplifies the air handling requirements for the transmitter building... but it is messy... and I for one, would just as soon avoid it. The coolant for the IOT above is a 50-50 mix of reagent grade ethylene glycol and distilled water. Anti-freeze is a no-no.... the additives in anti-freeze will cause problems with the tube cooling jackets and other components of the cooling system.

Regards,

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 Post subject: Re: First generation TV transmitters
PostPosted: Mar Tue 31, 2020 11:22 pm 
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Jim

Thanks for your addition and I agree with your comments.

Last weekend I had the pleasure of changing out an E2V D2100 that was working fine until the transmitter was shut down (Black Heat as Harris calles it) for a tower crew to climb near the antenna. Afrter a nice soft shutdown and a nice soft re-start the D2100 IOT which had well over 40,000 hours probably succomed to Covid news, popped off a couple of Crowbars and Cavity Arcs and is now in the Afterlife. We are now running a used tube as a new tube is $50,000 dollars, Then there is the finger stock, and the cooling hoses, and High Voltage wring that is suggested to be replaced.

The cavity Arcs are due to an internal arc in the tube and seen by the Arc photocells.

The early'r 25 volt FET's used by Larcan and others have become very difficult to buy. These come from China mnostly and China is closed.

Some of the early modulators would not perform adaptive correction properly and they would get their bandwidth outside the 6 MHz for the TV channel Before the VSWR trip could activate the reflected power would couple back through the combiners and promptly blow 500 FET's in a blink. They were going for well over $100. Electricity wasn't all that bad compared.

We run several all air cooled FET transmitters in our extremly hot city of Phoenix AZ. As we don't allow outside air into transmitter cooling, we have commercial air conditioning which eats up a lot of the electricity savings.

The new FET transmitters are generally liquid cooled which requires an outside pump and heat exchanger.

We cool the IOT transmitter with a 50:50 mix of DowTherm and Distilled water. Dowtherm is mostly Ethylene Glycol which is what I call Antifreez without some of the addatives required for aluminum car parts. I believe we can actually run regular distilled water in the transmitter cooling as we never reach freezing temperatures.

We still have the last RCA TTU-110 in place which was steam cooled. The steam from the Klystron collector was conveyed outside to a heat exchanger which condensed back to liquid water. As this water had been distilled over and over. It was what was called "hungery water' that would slowly etch the copper pipes.

Under the new ATSC1.0 and 3.0 rules, the FCC has lowered transmit power and the result is poor propogation in the VHF band. Some VHF broadcasters are scrambling to move into UHF and get about 1 Megawatt. FCC Re-pack has put a big strain on this.

Jim

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 Post subject: Re: First generation TV transmitters
PostPosted: Apr Wed 01, 2020 3:16 am 
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Greetings to Jim and the Forum:

Yeah... that sounds familiar. I remember several occasions where a tube wouldn't come back after being shut down for other reasons.... everything from a 1 watt reflex klystron in telco microwave service to a big transmitting tetrode (see my avatar) to an IOT-2100B. I feel your pain.

The Harris guys that did the install on our Sigma CD++ transmitters told me that one could not claim to be a real UHF engineer until one had taken one's first glycol shower. I guess I'm not a real UHF engineer since I managed to avoid that, but I think I got a couple of shirts pretty dirty. Lying on the floor in a puddle of coolant while trying to disconnect the collector cabling and the big coolant hoses will cause an amazing amount of dirt off the floor to soak into one's shirtsleeves.... but you know that.

I can't speak to the UHF solid-state transmitters because we never had any failures during the short time between their installation and when I was transferred down to the studio. The Diamond was a back-up transmitter to the Sigmas anyway, so it didn't see all that many hours.

The VHF Larcan (module in photo in previous post) used MRF-151G FETs.... and their drain voltage was 50 volts. We had lots of failures of those devices... I probably changed out upwards of a hundred of them. I actually built a test cart with a big Lambda 50 volt power supply, a load and a couple of wattmeters so that I could run one to a full KW in the shop. The cart also had an Angle Linear gain block so I could drive the module to full power with our HP 8712 network analyzer. That allowed us to see pretty well whether the unit was going to perform in service. Strangely enough, a lot of FET failures were such that the device could be biased correctly and make power, but the module bandwidth was terrible. I have no idea what the failure mechanism was, but a new FET (or FETs) cured the problem.

I am well aware of ion hungry distilled water. We had a Bird 50 KW "Moduload" dummy load / calorimeter. This was a nifty gadget when it worked... you could read power directly on a digital readout box that plugged into the load. Unfortunately, the required temperature sensors were TO-5 cans glued into plugs that threaded into the coolant piping. Bird required that distilled water be used in the load.... and those temp sensors were always developing pin hole leaks in the TO-5 cans. Whatever electronics was inside the can, it didn't like to work submerged in water.

Ahh... the good old days. I'm retired now, so I can remember the good times and block out the unpleasant ones.

Good luck with your used IOT-2100!

Regards,

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 Post subject: Re: First generation TV transmitters
PostPosted: Apr Wed 01, 2020 4:44 am 
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On those transmitters with a huge number of FETs:
Were those designed with the FETs in a bunch of modules such that you could loose some without the whole transmitter going down?

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 Post subject: Re: First generation TV transmitters
PostPosted: Apr Wed 01, 2020 5:18 am 
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Greetings to Tom and the Forum:

Yes.

In the case of the Larcan PA modules such as the one in the photo in my earlier post, what you can't see is the back side is two enormous heat sinks, with the fins running perpendicular to the long axis of the module. The modules go into shelves oriented edge up, so that the circuit board faces to the right and the heat sink fins are on the left. Cooling air moves vertically through two shelves, one above the other and out the top. If you have to remove a module, Larcan supplies a blank plate to cover up the hole so that air flow is not short-circuited away from the module below. The cooling air flow is what a marine engineer would call induced draft... that is, the blowers are on top of the cabinets and pull air up, through and out. The connector shown to the right of the module has pins of varying lengths so that control, Rf and power connections are sequenced when the module is inserted or removed.

Here's what the whole transmitter looks like:

Attachment:
Larcan Transmitter.jpg
Larcan Transmitter.jpg [ 77.16 KiB | Viewed 453 times ]


In the case of the Harris platinum, the air flow is horizontal, the modules are narrower and sit flat, and have a touch sensitive control surface built into the grab handle, so that when you wrap your fingers around the grip, the module shuts down. The transmitter keeps going. Here's what the module looks like:

Attachment:
Harris Platinum Module.jpg
Harris Platinum Module.jpg [ 152.31 KiB | Viewed 453 times ]


Here is a small (single cabinet) Harris Platinum transmitter.

Attachment:
Harris Platinum Transmitter.jpg
Harris Platinum Transmitter.jpg [ 73.49 KiB | Viewed 453 times ]


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 Post subject: Re: First generation TV transmitters
PostPosted: Apr Fri 03, 2020 3:48 pm 
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The FET Power Amplifier modules are usually 1 kW each. They are made of little strip line pallets. The module or drawer is a heavy aluminum heat sink. Each pallet has a dual ceramic FET with which is screwed and clamped directly to the heat sink. Since I believe it is the common drain it has to make good electrical contact with the heat sink.

The FET's can fail which kills a single pallet but the pallet keeps working at lower power and some signal distortion.

Each pallet has a bias circuit for the FET.. There can be a driver pallet and 6 to 8 final pallets per drawer. You are supposed to be able pop a drawer out with the transmitter at full power.

Jim


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 Post subject: Re: First generation TV transmitters
PostPosted: Apr Fri 03, 2020 11:37 pm 
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Greetings to the Forum:

To amplify on what Jim said, here's a close-up photo of a Larcan 1.5 KW PA module, specifically of two of six FET amplifiers that are combined by Wilkinson combiners. I took this photo to show a rather spectacular failure of one of the electrolytic decoupling capacitors used in each stage.

Attachment:
Larcan CapR.JPG
Larcan CapR.JPG [ 243.92 KiB | Viewed 400 times ]


However, I call your attention to the two fuses, one for each half of the FET and the two trim pots. The procedure for adjusting the FET bias for proper operation is to remove all the fuses except one from the PA module and with both the input and output terminated, the trim pot is adjusted for proper idling current as measured by metering a 50 volt DC supply to the module on the bench. The control electronics and bias voltage dividers draw a small amount of current and the FET bias is adjusted for approximately a 1/2 amp change when the fuse is snapped into its clips or lifted. The procedure is repeated for each half of all the FETs in the module.

I understand that the procedure for the Harris pallets is more difficult owing to the fact that the FETs are not fused individually. I never had to change a Harris FET, but I probably changed upwards of 100 Larcan Fets.

The screws in the metal "bridge" which goes over the FET package and which mount the FET to the heatsink and the center pressure screw in the bridge are all tightened with a precision torque screwdriver. Because the gate and source tabs are gold plated, a silver-bearing solder is required to avoid leaching the thin gold plating off the tabs.

And now that I've told you how to do my job, you can go apply at any station using Larcan transmitters. :D

Regards,

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