CS25-A (aka SPF) Portable RadiotelephoneSPECIFICATIONS
Type: CS-25A 107944-A radiotelephone
Frequency Range: 2890 kc to 3530 KHz
Transmitter Power Output: 2.5 watts
Circa:1938 - 1943
Comment: This is a Canadian clone of the American SPF set and was known to be used by the British Columbia Forestry Service (BCFS). In the US, the set was widely used by the United States Forest Service and the US Army although it never received BC or SCR designator. It was primarily used by Forest Service rangers and firefighters for voice communication between units in the field and base stations over short distances of perhaps 10 to 20 miles. Under BCFS nomenclature, SPF means "Sets, Portable, Forestry".
A version of the SPF was also made by VRL (Vancouver Radio Laboratories). They identified it as the "2AB RADIOPHONE". An example held by collector Tom Brent bears the Canadian Army broad arrow. "SPF" has of course, become a generic term for these radios which were built by two manufacturers in Canada and at least four in the U.S.
Knowing when a tube entered service can aid in establishing the date of a design.
|A complete unit.|
|General view of the front panel.|
|There was no calibrated frequency dial just a logging scale.|
|Back of case.|
|Another nameplate example.|
|All photos in this table courtesy E-bay|
THE SPF AS BUILT BY VANCOUVER RADIO LABS
|The complete 2AB unit.|
|Front panel closeup.|
|There are actually four transformers that are strapped together with a common bracket arrangement and when one transformer failed, a previous owner figured the easiest way to effect a repair (lacking a complete transformer assembly) was to cut it apart and replace the defective part. Therfore this section of the chassis is not "as-built".|
|The Canadian Army broad arrow can be seen in this rear view. The jack is for the key while the adjustment knob is the plate tuning capacitor (shown as C29 on the schematic).|
|All photos in this table by Tom Brent|
|Model 2AB schematic . Click on image to enlarge. (A VRL document provided by Tom Brent)|
THE SPF RADIO
The SPF Model AE radiotelephone used by the United States Forest Service was made by the Radio Specialty Mfg. Company of Portland, Oergon. Although it came in several variants , the Model SPF AE is the one featured in the photos below, This example is part of the collection of Joe Long WA2EJT.
|Above and below: The SPF radio was also used by the US Army Signal Corps. (Photos via E-bay)|
Contributors and Credits:
1) Joe Long WA2EJT <WA2EJT59(at)stny.rr.com>
2) Tube Lore by Ludwell SibleyISBN 0-9654683-0-5 1996
3) Tom Brent <tgb(at)telus.net>