|
|
MRHS NEWSLETTER No. 13
Dedicated to True Believers World Wide
28 August 2012
Newsletter Comments - And a Fair Warning Lots of readers have done us the honor of writing with comments about the Newsletter. One of the most common is that more technical detail is better! So fair warning, the article about the PW-15 transmitters below is stuffed with just that sort of thing.
As always, your comments and suggestions are most welcome. Just send an email message to info@radiomarine.org.
Newsletter Back Issues
You want 'em, we got 'em! (Starting with Newsletter No. 3, the first that wasn't a plain email message.). They're on line for your reading pleasure. Just click on the link below.
 | |
Newsletter Archive
|
Visit the MRHS Web Site
You say you're a True Believer? You say you enjoy the sort of thing we talk about here in the Newsletter? Then you'll probably enjoy our Web site too where there's tons more to see and look at. Check it out.
| | | MRHS Web Site |
SUPPORT THE MRHS
Press Wireless PW-15 Transmitters
And then... the riggers arrived. These guys were the picture of what you're looking for in a rigger. Just two of them were enough for a job that looked tremendously intimidating to us.
 | | The 17Mc PW-15 on the forklift ready for loading on the low boy trailer |
Quicker than we would have thought possible the two PW-15s were on the low boy, tied down and ready for the trip north to Bolinas.
 | | Both PW-15s ready for departure |
After a *mostly* uneventful trip up the freeway, through Golden Gate Park, across the Golden Gate Bridge and along the winding roads of West Marin county (buy us a beer to hear the full story!) the transmitters arrived safely at Bolinas.
 | | The first of the PW-15s about to enter the Bolinas transmitter building |
Tom had Steve had carefully measured the area available and marked out the spots for the transmitters. The riggers placed them exactly where they needed to be.
 | | The 12Mc (L) and 17Mc (R) PW-15s installed on the first floor of the transmitter building in Bolinas |
By a bit of good luck we had power for these transmitters readily available. On the floor above in the main transmitter gallery two vintage transmitters had been removed in 1990 to make space for two rows of new Henry HF5000D transmitters. But the power lines for these scrapped transmitters were still in the cable trough above the PW-15s. So those cables were redirected to the PW-15s and the circuit breakers for the old transmitters were re-labeled for the Press Wireless transmitters.
The PW-15s started life with a balanced output (the mechanical layout in the final stage cabinet to accomplish this is a wonder to behold with cranks, worm gears and other delightful stuff). But Globe Wireless had converted them to unbalanced (coaxial) output along with many other modifications to get them to meet tighter specifications in 1979. This made things easier for us as we could route a coaxial cable down from the floor above to connect with the transmitter. That's not quite as easy as it sounds since the standard cable at the Bolinas transmitter site is 7/8" Heliax. Still, that's easier to handle than the 1-5/8" cable used at the Globe Wireless site!
Now comes Mr. Steve Hawes, MRHS Transmitter Supervisor, with intimate technical details of the PW-15 - the kind radiomen like. He includes a bit of the history of our two transmitters as well.
Take it away, Steve...
There are two Press Wireless PW-15 transmitters in the collection at the Bolinas transmitter station. These transmitters were last used at the Globe Wireless transmitter site (MX) in Palo Alto. Here is some history and information on these units.
 | | Press Wireless transmitter site, Hicksville, L.L., N.Y. |
The PW-15 transmitters were manufactured by Press Wireless in Hicksville, L.I., N.Y. The Signal Corps. contract plate says 1942, and most of the parts have date codes of 1943. The units were rated at 15kW output from 4-22Mc, with balanced-line output.
The transmitters had an internal oven-stabilized oscillator with six selectable crystals or a VFO, or could be driven from external frequency source. The keying circuit in the transmitter used vacuum tubes and could key the transmitter at speeds up to 500 WPM. A keying shaper could be switched in or out. All of the power supplies used mercury vapor rectifiers. The frequency source was in the 2-4Mc range, and 1, 2 or 3 stages of frequency doubling was selected, depending on the final output frequency.
Tube complement included 866A, 872A and 575A rectifiers; 2A3 and 807 keyer and buffer, Amperex HF100 doublers (3), Amperex HF300 (push-pull) first amplifier (some units used 250T tubes), 889R (push-pull) PA. Keying could be on-off or FSK from external modulator and frequency source unit.
The PW-15 transmitters at the Globe Wireless site came from Press wireless Brentwood, L.I., N.Y. and Belmont CA sites, and a couple from the Globe Wireless KTK Mussel Rock Radio site. There were a total of twelve PW-15s at the Palo Alto site. The original use at Press Wireless and ITT/Mackay Radio was for point-to-point overseas circuits. The tuning records for the two transmitters we have show them having been used on frequencies from 5350kc to 23450kc. With the introduction of satellite circuits and the end of the point to point service, the transmitters became available for KFS ship to shore coast station use.
Over the years modifications were made by the ITT/KFS engineers, but 1979 saw major modifications to meet the new requirements for reduced occupied bandwidth and lower harmonic and spurious output. The overall modifications included replacing mercury rectifiers with solid-state assemblies, changing the tube complement to less expensive and more readily available types, and in 1979 changing the output to unbalanced 50-ohm coaxial and modifying the keying for less occupied bandwidth. These transmitters operated in the KFS maritime Morse service until close of that service in 1999.
The tube complement at that point included 810s in the doublers, Amperex 5867As in the first amplifier and 8269s in the PA. The output power was rated at 10kW. Extra shielding was placed over the viewing windows and meters, tuned traps were installed for second harmonic reduction, and external low-pass filters were used to reduce higher harmonics. With these changes the transmitters met all technical requirements for FCC Part 80 stations.
In 2002 the MRHS started working with Globe Wireless to preserve two of the PW-15 transmitters and move them to the former RCA/KPH Bolinas transmitter site in the Point Reyes National Seashore. The MRHS is working with the Park Service to preserve, restore and interpret this historic site and its equipment. While PW-15s were never at the RCA Bolinas site, we have found correspondence in both the RCA and ITT files that indicates there were talks related to moving 8 PW-15s from Palo Alto to Bolinas Building 2 and renting space from RCA, but that never took place.
MRHS volunteers selected two PW-15 transmitters for preservation, S/N 12, SET 45 KFS 12B used on 12695.5kc and S/N 26, SET 44 KFS 17B used on 17184.0kc (both units with Press Wireless property tags). Heavy and delicate components were removed from the cabinet, many documentary pictures were taken and spare parts and documents were collected. The smaller parts were taken to Bolinas in our own vehicles.
In 2003 the MHRS used $3500 of its funds to hire a heavy equipment moving company to remove two transmitters from the KFS building, truck them to Bolinas and set them in the space we had prepared on the ground floor of building 2A. The MRHS also obtained the donation of other KFS and Mackay radio artifacts including point-to-point equipment, receivers, test equipment and the Harris transmitters used on 500kc. We obtained enough harmonic trap parts and the custom low-pass filters to put a PW-15 on any maritime band from 4 through 22Mc. It's good that we did because a recent inquiry revealed that nothing remains, not even scraps, of the PW-15 transmitters we left behind.
We also obtained the ITT 1200A frequency source units that had been used with the PW-15 transmitters. These are solid state units that produce about 1 watt of signal at 2-4Mc. They contain a high stability proportional control oven for the crystal and are also capable of frequency-shifting the signal for data transmission. The 1200A is installed in a rack in the control room on the floor above the PW-15s.
MRHS volunteers restored PW-15 12B and had it operational in 2004. Both transmitters we received had solid-state rectifiers in the 550v, 3kV, and bias supplies, but still had the 575A mercury vapor tubes in the 7kV supply.
Later, we decided to retro-modify the transmitter by putting back the mercury vapor rectifiers in the other power supplies. The rectifier filament transformers had been removed and the tube sockets modified. We collected suitable transformers, some from KFS parts stock with Press Wireless markings.
New tube sockets were installed, and some new wiring was added if the original was not still in place. The 12B transmitter now looks much as it did when first built, with the glow of mercury vapor visible through the viewing window screens. (We've also regained the maintenance headache of dealing with old and deteriorating mercury vapor tubes which require a lot of testing and selection.) After restoration, we operate the unit at 5kW, since KSM is licensed for that power, and also because most of the tubes are well used and we can't make much over 7kW.
The second PW-15, 17B, is being restored and is almost ready for power up. We will probably leave the solid-state power supply rectifiers as received from KFS, to provide an example of that period.
How often does a True Believer and dedicated radio squirrel get to work on a project like this? Right! Once in a lifetime. We fund work like this and the restoration all the other equipment and antennas out of our pockets - and we do so gladly. But every bit of support from fellow True Believers makes a big difference.
To all those who have sent along a contribution to The Cause we offer a heartfelt thanks. Your support is tremendously appreciated.
If you're a True Believer and can make a contribution to The Cause it will be most appreciated. And remember, we're all volunteers so 100% of your contribution goes directly to purchase the items needed to keep the transmitters and receivers working and the antennas in the air.
Tubes Donated to the MRHS
As we've reported in earlier numbers of the Newsletter, True Believers across the country have generously donated items of equipment to help the MRHS expand its inventory of historically important items that have a relationship to KPH or other aspects of radio history. But keeping these items in operation requires spare parts.
Now comes Mr. Terry Ward who contacted us with the offer of a large quantity of vacuum tubes. When this offer was mentioned to the radio squirrels at the MRHS it was like showing a chicken to a school of piranha. The offer was immediately accepted!
In return, we offered to pay the shipping costs for the tubes. But in a most moving gesture, Terry said he'd like to cover the shipping in honor of his father who served in the US Navy during WWII as Communications Officer on  | Lieutenant Junior Grade
George G. Ward, USN |
What can you say to an offer like that? We figured "of course" and "thanks" were the only worthy responses. The boxes of tubes have arrived - all SEVEN of them! The tubes will be carefully stored and inventoried for future use.
Mr. and Mrs. America and all the ships at sea... let's go to press with the KSM and K6KPH report for Saturday 25 August 2012...
It was a day of longer contacts rather than more contacts. And it was a day of QRP (low powered) contacts. The QRP part began with an email from Stan, the operator at WB2LQF. He said he's been trying to get us for weeks. So we set up a listening watch for him and contact was finally made with much pleasure at both ends of the circuit. KJ5XF and WA6SVX also made the grade with their low powered transmitters. With the 1.5kW TPO of K6KPH we guess you have to call those asymmetrical contacts but they were all the more fun for that. On the commercial side KKUI came up on 12Mc as usual for a signal check with KSM. "Usual" is the operative word here because this time there was only one KKUI and they actually heard us on the same band they were calling on. In the past there have been two signals identifying as KKUI and one of them replied only when we answered their 12Mc call on 16Mc! Speaking of the unusual and unidentified, "cat stepping" was observed on 500kc (which we of course constantly monitor). The feline term derives from the sounds the vintage radio consoles (like the Radiomarine 3U and 4U units) make when the medium frequency transmitter is being tuned up. Someone once said "that sounds like someone is stepping on a cat" and the term stuck. Anyway, the stepping did not result in a contact or even an identification of who it was. No cats were actually harmed in this sequence.
Let's take a look at the log. FW = Rick Wahl, RD = Richard Dillman. The numbers in (parenthesis) indicate the frequency band in use. R1, etc. means that a radiogram was received. UNRAISE means that we couldn't raise the station. K6CPA had a great signal on 7Mc but when we replied it seemed he couldn't hear us.
KSM
1923 KKUI (12)
POS 1 RD
2213 N6BBF (7) R1
2219 KB6C (7)
2230 K6CPA UNRAISE (7)
POS 4 FW
1907 W4LNI (14)
1920 W8IM R1 NR 78 (21)
1935 KJ5XF 3W (21)
2009 WA6SVX 2W (7)
2118 WB2LQF 5W (14)
2130 N5XE (21)
Here's the radiogram we received from W8IM:
NR 78 R W8IM 16/14 LEESBURG FL AUG 25
KSM VIA K6KPH
FLORIDA SWL REPORT KSM SATURDAY AUG 25 1900 GMT 12/22 QSA4 16 QSA5 73
DAN
Hey you! Yeah you, the guy wearing the earphones! Are you a CW op yearning to sling some Morse at the "code factory" (as KPH was once called)? If you are we have an operating position all set up just for you. Bring your key and cans or use ours. Just drop a line to info@radiomarine.org to let us know you're coming.
VY 73,
MRHS Operating Department
NOTE: KSM and K6KPH will be active on Saturdays only until further notice.
Until next week we wish you fair winds and following seas.
MRHS
Had quite enough of this dull and boring radio drivel? Want to unsubscribe? Sure! Just click on the "Safe Unsubscribe" button below.
|
|
|
|
|
|
|
|
|
|
|
|
|
