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RCA BTA-50G question

A

amfmsw

This is a copy of a conversation on the Philly board. Can someone answer it?

Quote from: rtetro on December 22, 2007, 10:51:01 pm
I'd be willing to donate a Storer Broadcasting built Negative Peak Limiter to the cause that has received innumerable hours of testing on an RCA BTA-50G Ampliphase transmitter. Guaranteed to keep the negatives at 99% while the postives hit 300%.



Rene,
I was under the understanding that Ampliphase transmitters couldn't modulate over 100% positive. Did the BTA-50G have to be modified at some point for greater modulation peaks
 
I've had quite a bit of experience with the 50G. It could modulate in the positive direction over 100% but it tended to splatter as the IMD was quite high.
That's why is was called "AMPLIFUZZ."
 
The 50G had marginal driver tubes and a very marginal power supply. I had one with all new tubes and pristinely tuned up occasionally hit 115% positive for a few weeks, but then it settled back down to 105%.

The 50H was quite another matter however. It had 4CX5000s for drivers and a much better power supply. They could do 115-120% positive all day. Some 50Hs (including the one at 1510 in Boston) had a 100 kW power supply. Those rigs could easily do 130-140% positive at 52.5 kW out.
 
In my case, at 540 WGTO, Cypress Gardens, Florida ....
We disconnected the RF detector inverse feedback network as it made the transmitter less stable into our antenna system.
The Ampliphase worked well only when the sideband response was balanced. In our case, we installed a phase rotation network at the common point to correct for the sideband imbalance.
Unfortunately, this network wasn't installed until the 50G was replaced with a Gates MW50. The MW50 could not reach 100% negative modulation until the network was installed.
The BTA 50H was a far better transmitter. It had better PA and driver tubes. The 50G was a "dog."
 
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