Broadcast transmitter question

[KE8BNE]

I may have an opportunity to get an RCA BTA 500M.  What is typically involved in converting a commercial transmitter to amateur use ?
I have not made an offer on it, my contact says it was complete and functional when removed from service.

[K8DI]

I went down this road with an RCA BTA 1R1, a 1000 watt newer version. It made its on air debut for last February’s AM rally.

My quick thoughts: 
It will take MUCH longer than you think, seems reasonable, etc.
It will cost MUCH more than you think, seems reasonable, etc.
You will learn MUCH more about RF and transmitter design than you expected.
You will lean on people here and other forums for advice and help.  Most, but not all, of the advice will be good.

Steps:
Study the manual
Fix whatever looks broke
Study the manual
Test every part
Study the manual
Try to get it operating as designed (on original AM freq)
Study the manual and some related manuals
Get it 100% on air on original freq (dummy load of course)
Study a lot of manuals and circuits
Figure out new tank
Figure out new RF drive
Study more
Test
Fail
Test
Fail
Study
Test
Succeed sorta
Study
Refigure tank and drive
Test
Study
Test
Succeed!!!!!

Figure out how to make it play with a receiver

Get on the air!

Have fun, ask questions, and good luck!

Ed
With an RCA BTA1R1, 80/40/20 multiband modified beast in his shack…

[KE8BNE]

Thanks for the reply Ed, & congratulations on getting yours on the air.   

Yeah, I certainly will have many questions.  Is a project such as this worth pursuing or would it be better to build something from the ground up ? I know that is a very subjective question. 
I have found that the learning is the fun part, sometimes frustrating too.   I will have to think a bit on this project, before putting an offer on it.

I have tried to get in on a couple AM nets in the mornings with a Hallicrafters HT-32A, but I am often just not out of the noise enough. I figure something like this will certainly provide the parts to get me going in the right direction.

[K8DI]

Thanks for the reply Ed, & congratulations on getting yours on the air.   

Yeah, I certainly will have many questions.  Is a project such as this worth pursuing or would it be better to build something from the ground up ?

The big difference, is that with an intact transmitter, you have all the parts. Big iron, both for power, modulation, and chokes, is hard to find and expensive to ship.  Building from scratch is great, IF you have/can get ALL the parts.  I kinda gave up on building an 813 based rig because after two years, I was still short on parts.  Besides the cool factor, what the RCA got me was a working, populated chassis…

Is it worth it?  As you said, it’s subjective.  For me, it’s a “Hell, yeah!” It was totally worth it.  I’d do it again if my wife would let me take up more space with a second one, and a third…a Gates, a Bauer, maybe even a Westinghouse!

Ed

[KD1SH]

  I’ll humbly preface my comments on scratch-building with an admission that, in scratch-building experience, I’m light-years behind guys like Ed, or Tom, K1JJ, for example, but here’s my take on it:
  Before you can even begin to get your rig functioning electrically, you’ve got to do the mechanical work, and up until the moment you sit yourself down in front of an empty cabinet; a virgin chassis; a couple of vacuum variables; a roller inductor; tube sockets (and the tubes, for measurement); filament transformers; plate chokes—all of which need to have their space—it’s very easy to massively underestimate the magnitude of the undertaking.
  Expect to spend hours carefully pencil-marking the outlines of the various parts on the chassis; measuring and outlining the holes you’ll need to make in the front panel; making cardboard or 1/8” plywood mockups to test whether it all fits, and then, after all this, you’ll discover that you’ve forgotten to allow space behind the front panel for the meters, or room to route the shaft for your roller inductor. So, you press the reset button—everything gets all shifted around—rinse and repeat.
  Last year, I came home from Nearfest with the entire complement of iron—power and modulation—from a Gates BC-1T, along with the oil-filled caps and rectifiers. I’ve got everything I need, from vacuum variables to roller inductors; tubes to sockets; panel meters to turns-counting cranks, to build a very nice rig: three 813’s modulated by a pair of 810’s. I’m still drawing outlines of parts on the chassis; making cardboard mockups and measuring things, and that’s just for the RF deck—I haven’t even started on the modulator and power supply—and I realistically expect this project to take a couple of years, at best.
  With a commercially made BC transmitter you’ve still got a very serious project, like Ed said, but at least someone else has done the tedious physical layout, and there’s a lot to be said for that.

[W7TFO]

If you go for it, please take this advice:

Put it on casters.  NOT bolted just under the chassis, but outrigged with 4"x 3/8" steel plates long enough to stick out past the front and rear of the box.  And big commercial ones, not some little ones from Ace or the like.

You'll thank me when it comes time to service or clean behind it.  Been there/done that many times for big BC rigs.

A friend of mine did it the 'easy' way and tipped his TX over when pushing it along the floor, just hitting a big crack caused it to tip.  Just lucky it fell away from him...

73DG

[KA3EKH]

Be prepared to lift and move heavy components, along with working with high voltages! If you have not worked with broadcast transmitters find someone who has to help you.
I did a RCA BTA 1MX couple years back and ran that a while on 160, the MX used all 833 tubes in the PA and modulator and with little change was able to put it on 160, would have been more of a challenge going up to 80 or above. Don’t remember if the 1M had 833 or newer tubes like 4-400 or some power pentode or not, triodes just have a lot of inherent goodness on lower frequencies. I de-tuned the PA down to 375 watts and had no issues working anyone with 375 watts of carrier, figure that’s around 1 kW peak on AM anyway. Also was able to get audio to be flat out to 20 kHz although I used a NRSC filter to limit response to 10 kHz and had second and third harmonics down below 60 to 70 dB.
Have a web page with pictures and links to YouTube videos at:

http://staff.salisbury.edu/~rafantini/RCABTA.htm

Although don’t know if you would want to take any advice from me, suggested something on another thread and have been informed that I am basically a hack.

[w9jsw]

I built my 813 x 813 rig using Gates BC-1T Iron. Took the better part of 3 years to get it all going. Very satisfying. Lots of help from K1JJ and WA1GFZ, along with AC0OB... On my QRZ page if you are interested.

John

[KL7OF]

Get the transmitter....and stare at it..... You'll think of something...you won't regret it....I have done 3 BC rigs...I had no idea what to do or what was involved.. I'm still having fun....  Good Luck..Steve

[W3SLK]

My 2¢ worth of advice is this: If you are going to get a BC box, 1) Lift weights and get your muscle tone together. You will need it!; 2) Be prepared to set it at one frequency. They were designed that once put on freq. they weren't going to move unless the box was sold and retuned! Although the ones that use an 833 are ok, you are pretty much frequency limited to how far you can go and require a good neutralization. At least 4-400's can be used above 6M! I thought boxes like the 250K can at least go to 4000KC, and you can drop another 810 in there for good measure. Not the whopping 1K of carrier you want but may be able to squeeze another 250 watts out. 500W of carrier and you will be heard.
Now my intention is to build a rig using a single 833. I would at least use it for 160 & 75M, with a possibility of 40 if not too difficult. Cuts down on a lot of logistical problems right there.

[KD1SH]

Yes indeed: the underappreciated, underutilized "stare at it" approach. Whether I'm working on a transmitter or rebuilding the carburetor on my lawn tractor, I've achieved better results through an hour of staring at the thing than through a whole day of bumbling, half-cocked, half-baked false starts.
Stare at it; visualize it; turn it upside down and inside out in your mind's eye—Einstein's gedankenexperiment—before you start drilling and blasting. It's time well spent.

Get the transmitter....and stare at it..... You'll think of something...you won't regret it....I have done 3 BC rigs...I had no idea what to do or what was involved.. I'm still having fun....  Good Luck..Steve

[Opcom]

If you go for it, please take this advice:

Put it on casters.  NOT bolted just under the chassis, but outrigged with 4"x 3/8" steel plates long enough to stick out past the front and rear of the box.  And big commercial ones, not some little ones from Ace or the like.

You'll thank me when it comes time to service or clean behind it.  Been there/done that many times for big BC rigs.

A friend of mine did it the 'easy' way and tipped his TX over when pushing it along the floor, just hitting a big crack caused it to tip.  Just lucky it fell away from him...

73DG

When tilting a BTA-250 transmitter over to get it through the door, it tipped over and fell on me. This was despite having three other people helping. It hurt, alot. It really was a bad thing and the bruises and lingering pain/discomfort remained for weeks. Upside is I cushioned it from hitting the concrete floor and it was not damaged. That unit is light in weight compared to a 500 or anything larger.

[KE8BNE]

W7TFO I like the suggestion of putting it on heavy duty casters & keeping them outboard.

[K8DI]

Couple followup notes:

KD1SH, your appreciation of my skills is appreciated, but I'm also light years behind K1JJ..Tom's a top builder, I just try hard!

KL7OF, I too use an enormous amount of "stare at it"..you need to 'see' the power and signal flows, in the box, to really 'get it' before taking actual actions..

I'm also pro HD castors..but I think whether you really need outriggers is case-dependent -- For example, my BTA-1R1 has angle iron feet on the sides, and wire ducts front and rear. So castors are mounted up in the recess between all that, directly to the 1/4" steel base plate -- meaning the height increased by only 3/4" which means the center of gravity wasn't raised six inches like would be the case with a flat-bottomed transmitter or castor board.  There's also some variation on top-heaviness, kW iron may be heavier than 250w iron, etc., but I am very comfortable rolling mine around.

The comment on hitting the gym is valid; if your mind's age is a small fraction of your body's age, you should maybe tell your mind to think twice...I have to remind myself of this when I see a mirror and wonder who that old fart is..

Anyway, because I hate the idea of BCB transmitters hitting the recycle/trash heap, I am very pro anyone getting one back on the air. If Greg/KE8BNE or anyone else wants to put up with my opinions and rambling, I'll be glad to offer what assistance I can.

Ed