Broadcast Transmitters
See My Newest addition to the Broadcast Family Updated March 19, '02
It all started in 1999 with my trip to Idaho to retrieve a Collins 20V from almost certain perill. I had posted mail to several sources, that if anyone had any old, retired broadcast rigs that were due to be "disposed" of, that they contact me before they did so so that I may "aquire" it and begin my next project: to convert one of these Iron Maidens to the 75M band. I had 2 replies. One is described below relating to the RCA BTA-1R, and the second was from an engineer named Rocky, who was looking after several stations in Idaho. He explained that one of his stations had an old Collins 20V, in rather rough shape, that could use some tender loving care to revive her to her former glory. It was more than the station wanted to spend so a price was set and off I went to retrieve it. I left Saturday morning, drove all day (1000Km), met Rocky, loaded the transmitter, had dinner and started the trip back. I made it about 50 miles and decided to stop for the night at around 9:30 p.m.. It was a most picturesque camp site that I chose, right next to the Snake river, on the Oregon side, about 1/2 mile from the interstate, and right across the river was a major rail line which provided great entertainment every hour or so. (one of my many other interests) By Sunday night I was beat after driving over 2000KM in 2 days so I waited until the next day to unload the Collins 20V. It made it into the garage with about 1" to clear the door, positioned it out of the way until I had time to get to it, and there it sat for 2 years. :-(
I never did get around to restoring it.
"California Dreamin'"
Meanwhile, I had heard that the old Bauer 707 transmitters were quite a bit smaller, 30"X25"X75" and only 800lbs! The Collins 20V is somewhere around 1300lbs. I focused my search for one of these which included many, many telephone calls to various stations in the northwest, emails and postings. I found 5 or 6, most of which were still in service, either as backup or as mains. I did however get very lucky when I discovered one in Fresno, that was now retired, but retired with many miles still to go on the clock. Just the rig I was looking for! It took over a year to finally obtain permission from the station's owners to remove the transmitter, but was well worth the wait. Engineer Scott, had kept it well maintained and it was in surprisingly good condition. In my search for the Bauer, I came across several other transmitters, one of which was a Collins 820D-2 in Arizona, which I found out was a favourite with my good friend Mike, KO6NM. I knew Mike was very keen on this rig as he has worked on them before at his Wisconsin QTH so I offered to give this one to him to help him get on the air in his California home. Mike was thrilled and immediately went to retrieve it. (see ER April 2001 for the complete story)
Meanwhile, the Fresno Bauer was just sitting there, waiting to be picked up so I asked if Mike would be able to go and get it. He said sure and it was back in LA within a few weeks. Now I just needed to find time to take off work to go get this, or figure out how to ship it. It was only a month later that the company I was working for, decided they needed to cut back on their staff count and I was part of a mass layoff. Mmmm. How things all work out for the best sometimes. I now had lot's of time to go get my baby!
It was July 5th 2:00 p.m. when I crossed the border heading south, I had just been to the doctor with my wife to check on the progress of our impending family member and was feeling very emotional about leaving her behind to go get an old chuck of iron so I focused on the task at hand: driving 2000KM to LA in 1 1/2 days. I arrived at Mike's house Friday night at 10:00 p.m. with my Collins 20V in tow, which I had offered to him in trade for some other goodies he had. I decided to put Bill Gates to the test and used Street's and Trips, combined with my GPS and laptop, and drove straight to Mike's place. It worked amazingly well! He was excited to see me and before I even had a chance to have a coffee, beer or restroom break, he and his friends were standing at the back of my truck with a dolly, ready to unload the Collins. I was amazed at thier energy level for 10:00 p.m. on a Friday night but after staying with Mike for a few days, I discovered the secret....Coffee and cigarettes. :-)
Mike's friend Dennis was the recipient of the new/old Collins and he was hard at work the next day completely stripping and cleaning the unit, but this is the story about a Bauer so sorry Dennis, I'll complete your story later. Okay...maybe just one picture of the 20V.
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I took this picture just so my wife could see that yes, a 1KW AM broadcast transmitter really does fit in the kitchen. It was actually in transit from the front to the back yard but I thought it was a rare sight. |
Saturday morning's dawn revealed my Bauer's true condition, which under the dirt, I could see was excellent. It was only a few hours before I had the meters stripped and tubes removed, ready for Mike's special treatment. It was here that I learned how to REALLY clean electronics. Have alook at the pictures!
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And here it is after a few hours in the hot California sun. Ready to power up and test on it's original frequency, before moving it to the ham bands.
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Mmmmm? Probably not many transmitters have this much water running through them.
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Mmmmm? Seems like there is still a lot of room in the truck. Shame to head home, 3000Km away, with only a partial load. Maybe a call to a few more stations is in order. Well, one of the stations I had called a year earlier, who I discovered had a Bauer as well as a backup, actually offered to pay me to remove their old transmitter. They currently have BE and the old Bauer has been dead for a few years, according to the log. |
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I didn't accpet any payment but did remove the old Bauer from the shack in the middle of a hot desolate field, in the middle of summer. Yes, it was very hot in the shack despite the A/C.
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This is the shack as I found it. Unfortunately, the Bauer was still connected to 240VAC and was also still in line (RF) with the new TX. ARG! Now what? I called the station manager and explained the situation. He said that it would be okay to take the station off the air for a few minutes if I did it during one of their satellite broadcasts during the noon hour. I had my tool box, and found some copper sheeting and braid in the shack, a trouble light and black tape. |
The biggest problem was there was no heliax to make the bridge from the old TX to the new one, or from the antenna tuner to the new TX, so I would have to make a splice and leave the new cable job for the regular eng who would be in on the weekend. The cable on the left is from the antenna and the one on the right goes to the BE TX. I gathered all raw materials, tools and a light, composed a plan of attack and waited for the signal from the studio. It came 10 minutes later, I shut down the BE, shut off the breakers, cut the AC to the Bauer, removed the Heliax, made up the splice, (see below. not bad for 1 minutes work), turned on the AC, fired up the BE and they were back on the air within 5 minutes. Phew! The plan worked and I could now resume removal of the old Bauer from the building. |
| Here is my splice. It only had to make it to the weekend. I was quite happy to see the SWR still at 1.05:1, just as it was before the removal. |  |
Conversion to 75M
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Here is my temporary mod to see if it would work. It did. I built a tank circuit for both the buffer and the driver stages tuned for 75M, to increase the output of each stage and provide a nice clean signal. I now have a perfect sine wave and 25mA of grid drive to the 4-400's! It wasn't this good in it's stock form. I will redo the mods in a neater fashion with buss bar once everything proves out 100%. |
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This is the new RFC PA choke that I built. It is on 2 different size coil forms and made with #22 wire. The old choke resonated close to the operating frequency and thus became very hot after a while. The white stuff is what happens when you use 30 year old Q-dope on the windings. :-( The coil stays nice and cool now and the PA loads much better. |
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This is the remote PTT circuit I built to allow much more friendly operation. I use a large footswitch to start this relay which has an "instant on" set of contacts as well as the time delay contacts on the top. This allows the the antenna to switch over and then .5 second later the PA comes on. I use an extra set of contacts to switch out the relay that changes the crystals so that there is no oscillator running while receiving. |
I just finished getting the PA stage tuned today and will detail it here soon. I ended up going back to basics and using a PI output networks rather than the PI-L for now. There were just too many variables for me to play with. I have everything tuned up perfect now on 3870KHz with the PI and will try to now tune up the L circuit to work with it. More to follow. |
To Be Continued........ That's engineer Scott and the Bauer in the old transmitter shack.
