[BC] Continental Hi-Power FM Tubes

[John Lyles]

I remember seeing that big cavity amplifier at NAB. I took photos of it as Dave Russell showed me around it. It was an impressive single tube FM! There were corona rings on the edges of the inner conductor of the half-wave cavity. At the time BE was curious, as they (we?) had half-wave circuits in all FM rigs, 
but without the problems of the Continental circuit.  The 4CX40,000G was the biggest air-cooled tetrode made, at 55 lbs! The 4CX35,000C used in 317C's was only 50 lbs. BE was satisfied with the 8990/4CX20,000A, being the first commercial user of that tube. It ran great at 30 kW, with << 12 kW of plate dissipation, although the Harris folks down the street tried to make a stink about using the tube too close to ratings, etc, until they listened to the customers. 4CX20,000A has a 1400 watt filament. Yet, Continental went to using the YC130/9019 tetrode at 35 kW, essentially a 4CX15,000 on steroids. It had a 1200 watt filament. I thought that CEC was under Varian ownership at the time, maybe that helped with the decision. Subsequently, there are numerous 4CX20,000 variants in the Eimac catalog (A-E) as no one wanted to use the wimpy 8990/A version that BE was breaking ground with. I think BE continued to use the A version in the FM30 until present. They used the 4CX20,000C in t!
 heir FM35
later. Hot tubes were so much fine, alas, now being replaced by cold silicon. I still design amplifiers using tubes, but at higher power levels. You can count the thermionic HPA designers remaining at work, with your hands.   
Regards
John Lyles

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From: Dave Hultsman <DHults1043 at aol.com>
The Factory gave them a recall.  The "Q" of the grid circuit was terrible.   The design engineer used a 1/2 wave cavity that liked to arc internally and Eimac forgot how to make the tubes and raised the price from $5,500 to 9500.00 in 3 years.   There were 13 sold. Aall stations were offered trade-ins based on their usage of the transmitters and trading up to parallel transmitters of 60 kW.  We already had made several parallel 35 kWs for 70 kW.  After about 5 years of tube problems it didn't appear to the industry or CEC that Eimac was going to get back to the 50-60,000 hours on the first three transmitters at WFOX (2) and WYAY in Atlanta.

All of the stations but one accepted the offer from Continental based on the records and reliability of the 816R parallel transmitters.  At one time Continental had more parallel transmitters in the field than any other single manufacturer.   The one company that didn't accept the offer tried to sell the used 817-A on the market as used.  CEC said they no longer supported or had any parts for the 817-A to all that inquired about the used rig.  The owner later traded it to CEC for the deal and a 35 kW. transmitter.
CEC backed the product, but most of the problem was the tube. The tube reps came out to a NAB party at the site where three of the transmitters operated near Atlanta and there were six duds stacked in the storage room.
Dave Hultsman