Unbelievable Henry Radio Amplifiers

One of the Rarest Of All…

Back in the day, if you were a Ham Operator or wanted to become one and you were in the L.A. area, Henry Radio, 11240 West Olympic Blvd. Los Angeles, was THE place to hang out.

From the time I was a small boy excited about ham radio, there was practically nothing more fun than visiting Henry Radio. I wrote my very first personal check at the counter of Henry Radio and I think one of my first stops when I got my drivers license, was down to Henry.

I can remember as if it were yesterday, pulling into the back parking lot and parking next to the great big Cadillac of one of our greatest hams, the late Don Wallace W6AM, (America Mexico). Looking in the driver's window and seeing his Swan 400 set up and that lightning bug strapped to the seat. You had to be there.

You'd walk in the back door, down the ramp and into a young ham operator's heaven. The Collins behind glass cases, the used vintage gear rooms and usually a Henry amp sitting on the floor to dream about. My dad helped me buy my first real equipment, a used Hammarlund HQ-170AC and a BW-5100B right there. Forty years later, the rest as they say is history.

Ted Henry W6UOU and his brothers gave us a great experience, no doubt about it.

For many of us around the world, Henry was also known for their great amplifiers. Build right there in L.A. at a separate facility down the road. For many of us, there was nothing finer than owning a Henry 2K amp, maybe a 4K if you were wealthy enough back then.

Before I could drive a car, I would bicycle for miles down to the Henry factory to get help on building my first home brew amps and when I was lucky, even buying some parts for my project.

Henry had one of the top RF design engineers back then. If I remember correctly, Bob Adams was his name. That was a long time ago. I can remember Bob drawing out schematics for me, helping me build a plate supply and even walking around the factory giving me a handful of parts to help me out. It doesn't get any better than that for a young general class.

Everyone remembers the Henry amps. From the first 2K's, 3K's to the beautiful 4K-Ultra all designed by Bob as I recall, and finally up to the remote tuned 8K, designed years after Bob had passed on. Henry was also known for manufacturing a series of medical and industrial RF generators and you still see a few surface in the classifieds from time to time.

But there was something else going on at the Henry factory back in the day and you probably never knew about that until now.

When the brilliant Bob Adams was engineering all those RF amplifiers, Henry also built a few VERY SPECIAL pieces on rare occasion. Those amplifiers weren't in any catalogs and you would not find one sitting on the floor at the store!

These amplifiers were absolutely special order, one off designs, and no doubt built for special purpose and probably commercial contract. Probably only a handful of these rare amplifiers were ever made.

The Henry built amplifier pictured here is one of them. If you want rare, then this is as rare as it gets. Only one was ever built. This is the Henry Radio 16K.

The Special Order Henry Radio 16K pictured here, was designed and engineered by Bob Adams and built at the original Henry factory. Records indicate that the amplifier was designed and custom built around March or April 1969.

The 16K was unique in many ways and reflected the classic design techniques of Bob Adams. It was to be an HF RF linear amplifier capable of more than 10 thousand watts output, continuous service duty cycle cw, rtty and ssb, 6 KW AM. Frequency coverage spec'd at 3.0 mhz to 25.0 mhz. This was no average duty cycle amateur class amplifier.

You can tell the Bob Adams design by noting the absence of any band switching, using only Tuning and Loading. The same design technique that Bob developed for the 4K Ultra later on.

The 16K was designed around a pair of Eimac 5CX3000A radial-beam power pentodes. Each tube has 4000 WATTS plate dissipation, 175 WATTS screen dissipation, 100 WATTS suppressor dissipation and 50 WATTS grid dissipation, 7000 VOLTS on the plates.

No doubt they selected the pentodes because of their excellent IMD characteristics in ssb and running AB1, the modest drive requirements of probably around 75 WATTS for full output, with reasonable plate voltage potential requirements.

Notice on the 16K photos, the adjustable bias and screen supplies. The amp could be throttled back to limit its peak power input form around 2000 watts up to more than 16000 watts.

The tuning and loading was also unique and creative by Bob Adams. Notice the tuning control used push buttons to control motor driven servos that drove the entire input tank circuit as well as the PI-L output tank circuit, (all tracking together). The tuning side was also set up to be remote controlled. The loading was more conventional and was used to trim the final output resonance.

Metering was through four front meters and included time meters to track both filament and operating hours, located inside the rear of the amplifier. Original shop photos show the finished amp with that appearance. These photos show additional metering which evidently was added at some point by others. The added meters read filament and operating time and primary input voltage.

The construction was absolutely first class. No expense was spared on parts selection or cooling. The RF compartment was a work of art. The main motor driven tank inductor was huge, about 10" or 12" in diameter, close to two feet in length standing vertical and all silver plated ½" diameter copper inductor. The L section tank was equally massive. The capacitors were the best ultra high RF current ceramic Jennings units as were the relays. Every other component was of the same class. Power output was monitored with Bird Electronics also designed for remote monitoring of the amplifiers output power.

Power supplies were massive as well, designed to operate continuous duty. Doubled up oil filled capacitor filtering, tuned chokes, quadruple rectifier banks, three phase 16 kva plus transformers designed to handle more than 2.6 amps. Plate supply on the bottom deck, the mid level supplies and control systems located on two separate decks.

Cooling was also impressive and far beyond any ham type amplifier for certain. The forced air cooling used a special very high volume blower designed to run with high back pressures located under the RF deck to cool the pair of 5CX3000A tubes running full tilt. Two additional 10" cooling exhaust fans were located on the amplifier roof to expel hot air. This thing must have put out plenty of heat. In class AB1 ssb, the amplifier was designed to idle at more than 7000 WATTS. That's before any drive was even applied!

The amplifier stood 6 feet tall, was 30" wide and approximately 3 feet in depth. The weight, who knows for sure, but a guess would be probably around 900 to 1000 lbs complete.

It is believed that the 16K eventually was sold by the original contract customer and held in private collections for many years. Today the current whereabouts of this beautiful Henry amplifier are unknown. One only hopes that it has survived as a memory of a piece of Henry Radio history. I hope you've enjoyed reading about the 16K as much as I've enjoyed sharing with you a few of my memories of Henry Radio.

Author: Mr. Gary L. Goldsmith, W6UH
For: MyHamRadioSpace.com, 2008