In the late 50's I was the part time evening engineer for WGBB, 813 with 811 modulators, in Freeport NY.
WOW, that must have been a home brew commercial transmitter.
I knew of one using 805 mods and 813 in the final and was said to be home brew. I wonder how they got that past the FCC?
Sorry for dredging up an old thread but sometime it's nice to do so.
What's wrong with an old thread if the content is still interesting and relevant? Newer isn't always better. They have the same unexplainable hang-up on QRZ.com. There is now a 60-day time limit on threads because people would sometimes resurrect old ones.
The broadcast engineering term for a homebrew transmitter is "composite transmitter". I believe they are still legal to this day. You just have to build it to certain FCC specs, document everything, and run a proof of performance. The black wrinkle cabinet, meters, dials and name plates on my homebrew HF-300 transmitter came from a late 1930s 250 watt "composite" broadcast transmitter, obviously built from parts that were already "vintage" by the time it was first constructed. Some of the original parts are incorporated in the present transmitter, but fortunately/unfortunately, another ham got to the transmitter before I did.
Fortunately, because he rescued it from the broadcast transmitter site in 1960, just before it was about to be hauled to the dump. Unfortunately, because he had zero interest in or appreciation for vintage radio equipment. He completely gutted the original transmitter for parts, and then reconstructed his own homebrew transmitter into the cabinet. He worked for the phone company, so he acquired some of that ugly telephone company grey paint and sprayed it over the original black wrinkle.
When I got it in 1970, he had dismantled his homebrew rig, and the empty shell was sitting in his garage. He said he was about to take out the meters and trash the rest. I swapped him a box full of old panel meters for it. He did let me have some of the original BC transmitter parts, including the UTC LS-103 50 Hy 500MA modulation reactor, but he wouldn't let go of some of the other stuff, and he had already got rid of a lot of the rest.
I brought the remains home, and re-built my own homebrew transmitter into the old cabinet. I used my own design, using as many parts of the same vintage as the original as possible, but I didn't have any documentation on the old transmitter, so I made it into a 1 kw plate modulated rig with push-pull finals and plug-in coils, pretty much of my own mid-to-late 30s design. I stripped down the crudely built cabinet, re-enforced and squared it up the best I could, leaded up some of the extraneous holes the previous ham owner had drilled in the front panel, and re-painted it black wrinkle. Unfortunately, a large stripe on the front panel didn't wrinkle, and I tried to patch it up but just made it worse. I keep saying that some day I'll re-do the front, but it would take a tremendous amount of work to remove everything to repaint it, so that's a back-burner project that has been sitting on that back burner now for over 35 years.
Regarding 811s vs 812s, RCA recommended using a pair of 812s in the final and modulating with a pair of 811s. I believe Gates built a 250-watt stand-by transmitter using that line-up. Timtron showed me one at one of the sites he used to work at. It looked more like ham radio construction than broadcast, but sounded pretty good. 811/812 series tubes probably were too small for a full time 250 watt transmitter. A 100 watter maybe, but most 250 watters used at least something the size of 810s for both modulator and final.
According to the previous ham owner, the homebrew broadcast transmitter I just described used three 203As in parallel in the final, driven by a single Taylor HD-203A. The driver tube was larger than the finals! The PA was modulated by a pair of 838s. Like 811(A)s, those are zero-bias triodes, identical to 805s but with the plate lead coming out the base instead of a plate cap on top.
