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Ross Revenge
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Five and Ten
Ampliphase Ten

100kw (RNI)
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*** The Ampliphase Ancestry ***

The BTA-50G Ampliphase

The BTA-50G was released in 1955, the first unit shipped to WINS, New York, on 28th December 1955, and went into service shortly afterwards. The unit was extensively described in the August 1955 issue of RCA's "Broadcast News", pages 54 - 59. One notable feature in the article is "Fig 5" as shown below, which shows the inside of the exciter cabinet.

The modulator chassis shown here is physically different than the one which was fitted to later transmitters, and it is not known if this was only a prototype, or if early units were shipped with this modulator. Note also the presence of the oscillator at the bottom of the cabinet, where the drive regulator was later to be situated. This tends to suggest that there was no drive regulator in this unit, a fact which is borne out by Fig 2 in the article, a block diagram of the transmitter. This block diagram also shows that a single phase modulator was used, followed by a tripler. The crystal was on the carrier frequency, hence a divider was fitted before the modulator stage. The tubes in this modulator were the 5692, 5693 and 1614 as used in the later design. The 6076 drivers can be seen above the modulator, the 4-250 intermediate stages on the 50G were behind the side panels and are not visible in this picture.

The June 1957 issue of "Broadcast News" also carried a feature on the 50G, but the pictures in that article show the later style modulator, and the drive regulator has mysteriously appeared in the bottom of the cabinets.

The transmitter also featured Mercury Arc rectifiers for all the high voltage supplies, of 2.5Kv, 5Kv and 15Kv. The rectifier cabinet housed no less than 18 such tubes, all fed from their own, highly insulated filament transformers, as shown in the diagram below.

Note also the heater panel on the rear of the door consisting of 4R41 to 4R47, to keep the ambient temperature high enough for the tubes to operate.

The PA tubes on the 50G were a pair of type 5671, first produced by RCA in 1947. These tubes had also been used on the previous plate modulated generation of transmitter, the BTA-50F. At over two feet long, and 16 inches in diameter, these certainly were a big tube.

If you can shine any light on any version of ampliphase please feel free to contact me. In particular I would appreciate handbooks and photographs for the five and ten.

I really appreciate all feedback to these pages. Thanks!

My email address is: "ampliphase [at] radio [dot] fm" or use the feedback form on the left menu.

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