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Five and Ten
Ampliphase Ten

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

The BHF-100A Shortwave Ampliphase

The BHF-100A shortwave ampliphase was available in 1962, but differed significantly from the standard AM ampliphases. This was due to both the different frequencies involved, and the need to operate over a wide frequency range with regular changes. Although from the front it is not much bigger than the 50Kw AM versions, it is much, much deeper. Part of this depth was required to house the four PA tubes, but there was also the need to have motorised adjustable coils and capacitors which could be set as required, either by front panel cranks or motor-drives. One of the drawbacks to the ampliphase in all guises, was that of a slight phase shift of either channel caused by mal-adjustment upsetting the final relationship, or by a reactive antenna reflected back into the the combing stage and matching unit having a similar effect. This was more pronounced on the SW sets due to the need for frequency agilty, both within the TX tuning, and within the antenna systems used.

The floor plan of an HF100 installation, also showing the outline size of the previous generation 50KW shortwave transmitter.

The block diagram of the BHF-100A.

Front view of the control panel, showing PA cathode and grid meters.

Only about 12 of these models were built, and even RCA engineering staff regarded it as an unmitigated disaster. One engineering prototype was built to prove the concept, but was sold by an over enthusiastic sales department before it had reached the state of being a commercial product. As if this was not bad enough, the first units were shipped to Rawalpindi in Pakistan and Nigeria for customer installation with an RCA engineer attending for the commissioning process. This scenario made the inevitable field modifications even more impractical and even worse, construction of the units was sub-contacted out to an RCA subsidiary in Italy to reduce the labour costs. Unfortnately, somewhere along the way, the specifcation for brass hardware and fittings was lost, and the units were assembled with steel fixtures. This meant that an almost entire rebuild of the cabinets was required on site before their operation was anywhere near satisfactory. Other initial units went to Thailand with similar results and and the fourth customer Vatican Radio had their units extensively modified at the Camden, New Jersey headquarters of RCA before they were shipped. In all 47 major field modifications were implemented on the early units, the end result being a fairly reliable and user friendly transmitter. As a result of this fiasco and huge loss of revenue and credibility RCA management pulled the plug on shortwave manufacturing and the worldwide support it entailed. These transmitters were produced at a time when great changes were happening within American industry, the broadcast market, and especially within RCA. It's interesting to note that when the first prototypes were made RCA were a turnkey broadcast supplier, manufacturing everything from microphone, consoles, tape and cartridge machines, studio-transmitter links, compressors/line amplifiers, transmitters, antenna's and even studio woodwork and cabinets. Within a few years of these transmitters being dropped, RCA's sole broadcast offerings were TV cameras, videotape, and domestic transmitters. There was little scope in the managerial world for long protracted product development plans by engineers.

Diagrams on this page were extracted from the August 1962 issue of RCA Broadcast News. A list of where some of these HF100's were delivered to is on my Anthology page.

My thanks to Tony Rock, a former RCA commissioning engineer who spent 15 months in Pakistan installing the first units for sharing the tale of woe. Thanks also to John Stanley and Roger Stubbe for further information.

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 would also like to find out more about the BBC/Marconi ampliphases of the 1950's.

I really appreciate all feedback to these pages. Thanks!