Press Wireless PW15 Transmitters

The Press Wireless PW15 transmitter was once the workhorse of the point to point service operated by Press Wireless and, later, Globe Wireless after they absorbed PreWi.  They are of 1940s vinage and saw heavy service during WWII.  A dozen PW15 were in service at the Globe Wireless transmitter site in Palo Alto, CA, south of San Francisco.  Some were converted to CW service and were in service on the "last day" of commercial Morse in the US when KPH, KFS, WNU and KLB closed Morse service on 12 July 1999.   See the Incredible Radio Tales section of this Web site for what it was like on that last day.

The MRHS recovered two of these magnificent transmitters from Palo Alto and transported them to the Bolinas transmitter site.  One has been completely restored and operates as the KSM 12Mc transmitter for special occasions.  We believe this must be the last operating PW15 in the world.  The PW15 other awaits restoration.

Here's the photo story of the transport of these two transmitters to Bolinas.

See a video of the PW15 being brought on line on the MRHS YouTube site at:

View all images as a slideshow

The Palo Alto transmitter site, MX on the wire, was established in 1921.  It once contained powerful arc transmitters and had an umbrella antenna supported by a mast more than 600ft tall.  On the date this photo was taken MRHS members were evaluating the transmitteras and other artifcats within that might be made available for preservation.

Tom Horsfall evaluates the PW15 12B transmitter, one of two the MRHS recovered.

Tom Horsfall and Transmitter Supervisor Steve Hawes examine the PW15 transformers.  Oil samples from each were sent out for analysis.  Luckily for us the oil contained no PCBs so we could bring them to the Bolinas site under Park Service rules.

MRHS members were able to get the two transmitters selected for recovery up on cribbing.  Then it was time to call in the experienced riggers for the actual move.

The riggers put the transmitters on skates, allowing them to be easily moved.

Here's the first transmitter headed out the door.

The riggers used a large fork lift to load the transmitters on a flat bed trailer.

Both transmitters loaded and secured for the drive through San Francico and across the Golden Gate bridge to Bolinas.

Upon arrival at Bolinas the truck was able to drive to the west entry door where the fork lift once again took over.

The fork lift unloaded the first transmitter and headed toward the door.

The first transmitter about ready to enter Building 2A at the Bolinas transmitter site.

The first transmitter passes through the door.

PW15 12B in place, destined to become the KSM 12Mc transmitter.

Both transmitters in place.

Steve Hawes makes some adjustments to the vacuum variable in the final output stage.

Steve begins the initial tune up.

The final stage tubes glow, waiting to generate serious RF.

The forward power Wattmeter needle comes up off the peg, finally settling at 5kW output.

Some of the parts we gathered to allow maintenance of the transmitters and restoraction of the second PW15.