CS25-A  (aka SPF) Portable Radiotelephone

 


SPECIFICATIONS

Type: CS-25A 107944-A radiotelephone
Frequency Range: 2890 kc to 3530 KHz
Transmitter Power Output: 2.5 watts
Circa:1938  - 1943
Specification: 107-945
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.
Receiver Tubes

IN5   6-10-1938
1A7  6-10-1938
3Q5  6-30-1939

  Transmitter  Tubes

1H4  5-4-1936
1J6   5-4-1936
1F5  5-4-1936 

THE SPF AS BUILT BY CANADIAN MARCONI
cs25_01_general.jpg
A complete unit. 
cs25_02_fpanel.jpg
General view of the front panel.
cs25_03_meter.jpg
Meter detail.
cs25_04_vernier.jpg
There was no calibrated frequency dial just a logging scale. 
cs25_06_back.jpg
Back of case.
cs25_05_nplate.jpg
Nameplate.
All photos in this table courtesy E-bay 

THE SPF AS BUILT BY VANCOUVER RADIO LABS

cs25_2ab_withlid_06.jpg
The complete 2AB unit. 
cs25_2ab_front_07.jpg
Front panel closeup. 
cs25_2ab_inside_05.jpg
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". 
cs25_2ab_rear_03a.jpg
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). 
cs25_2ab_case_08.jpg
Case exterior.
 All photos in this table by Tom Brent 
cs25_2ab_schematic.jpg 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.

Additional information on the SPF set can be found at the "Forest History Society" web page. Search on 'spf".

cs25_spf_entire_set.jpg
Complete set . The number 1007, on the case and the front panel, is the serial number.
cs25_spf_01_front.jpg
Front panel of SPF Model AE. 
cs25_spf_02_top.jpg
Top 
cs25_spf_03_top.jpg
Top back 
cs25_spf_04_top.jpg
Top left 
cs25_spf_05_bottom.jpg
Bottom
cs25_spf_06_tr_switch.jpg
Closeup of transmit-receive switch.
All photos in this table by Joe Long WA2EJT

 
spf_01.jpg
Above and below: The SPF radio was also used by the US Army Signal Corps.  (Photos via E-bay)
spf_02.jpg

 


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>
 

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Nov 29/16