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Impedance and Resistance Measurments
Of
Sound Powered Elements
"Balanced Armature" Elements used for crystal radio sets


Please note:

These measurements were measured at only one frequency (1 kHz. which is the industry standard).
Impedance will change as the frequency changes.
The measurements were made to show the difference in impedance within the same type and brand of element.
This list is a work in progress.


RCA

Manufacturer 
RCA
Unit
Number
Element
Number
Unit Type
Element
Type
AC Impedance 
@ 1 kHz.
with capacitor/without cap.
 DC Resistance
(ohms)
"Big Cans"  MI-2045
1
1
DT
mic
 na / 220
 7.9
 "
2
2
DT
mic
 na / 140
 8.3
 "
3
3
DT
mic
 na / 220
 8.3
 "
4
4
DT
mic
 na / 200
 8.1
"
5
27
DT
mic
na / 100
9.6







 "Big Cans"  MI-2045
1
5
DT
ear
 na / 3900
 88.1
 "
1
6
DT
ear
 na / 3000
 81.7
 "
2
7
DT
ear
 na / 3600
 78.5
 "
2
8
DT
ear
 na / 3000
 81.1
 "
3
9
DT
ear
 na / 300*
 81.5
"
5
23
DT
ear
na / 2000
91
"
5
24
DT
ear
na / 1800
95
"
6
25
DT
ear
na / 1000
99
"
6
26
DT
ear
na / 2000
86







Handsets  MI-2040
5
10
Handset
mic
 na / 850
 141.9
"
6
11
Handset
mic
 1800 / 1420
 142.2
 "
7
12
Handset
mic
1000 / 600 
 142.4
 "
8
13
Handset
mic
 na / 300
 70.2
 "
9
14
Handset
mic
 1400 / 3500
146.6
 "
10
15
Handset
mic
 na / 400
 81.9
 "
11
16
Handset
mic
 na / 265
 71.6
 "
12
17
Handset
mic
 na / 160
 49.5
 "
5
18
Handset
ear
 na / 2250
 94.2
 "
6
19
Handset
ear
 1800 / 1420
 142.2
 "
7
20
Handset
ear
 910 / 150
 87.2
"
8
21
Handset
ear
 na / 254
 48.3
"
9
22
Handset
ear
320 / 500
74.7
* Units marked with  *  may have problems.
This problem may be mechanical thus giving a bad reading.
 
 
 
 
 
United States Instrument (USI)

NEW !
United States Instruments (USI) Deck Talkers ("Big Cans")
Model #A-260 UA1614 (older model)
Ear Units

AC Impedance 
@ 1 kHz.
DC Resistance
(ohms)
780
64.8
1600
61.2
500*
60.5
260*
64.4
700
61.9
1200
56.4
1100
60.6
1100
60.4
1100
61.1
1100
57.6
1300
58.2
395*
63.4
1000
58.5
1300
60.0
1800
60.0
800
59.4
1300
58.5
1300
58.8
1200
59.9
700
59.1
900
not available
1100
not available
850
59.7
1200
not available
1200
59.5
1200
58.6
1200
57.7
1100
62.0
1220
63.5
1400
63.3
* Units marked with  *  may have problems.
This problem may be mechanical thus giving a bad reading.
 
 

NEW !
United States Instruments (USI) Deck Talkers ("Big Cans")
Model #A-260 UA1614 (older model)
Mic Units

AC Impedance 
@ 1 kHz.
DC Resistance
(ohms)
390
13.7
350
13.7
82
15.5
240
not available
192
15.8
150
15.8

 
 
 

United States Instruments (USI) Handsets
Models A560, A577, A257,and A333
Ear and Mic Units

Manufacturer 
United States Instruments (USI)
Unit
Number
Element
Number
Unit Type
Element
Type
AC Impedance 
@ 1 kHz.
DC Resistance
(ohms)
Comments
UA1614 type
na
8
Handset
ear
300
62.6
no ua #'s  "Receiver T"
"
1
11
Handset
mic
450
63.3
no ua #'s (handset 677)
"
2
13
Handset
mic
450
60.1
UA1614-1 (handset 560)
"
3
15
Handset
mic
680
64.8
UA1614-3 (Stromberg A257)
"
4
17
Handset
mic
240
61.4
UA1614-1 (Stromberg H203)
"
na
23
Handset
mic
1050
60
UA1614-1
"
na
24
Handset
ear
810
60.9
UA1614-1
"
na
1
Handset
mic
1200
63
UA1614-1
"
na
2
Handset
mic
246
61.5
UA1614-1
"
na
3
Handset
mic
750
63.1
UA1614-1
"
na
4
Handset
mic
2500
62.5
UA1614-15
"
na
6
Handset
mic
3500
65.6
UA1614-15
"
na
7
Handset
mic
1500
64.8
UA1614-15
"
1
12
Handset
mic
1450
61.5
UA1614-15 (handset 577)
"
2
14
Handset
mic
dead
dead
UA1614-1 (handset 560)
"
3
16
Handset
mic
900
92.3
UA1614-4 (Stromberg A257)
"
4
18
Handset
mic
750
62.1
UA1614-1 (Stromberg H203)
"
na
25
Handset
mic
1150
89.8
UA1614-4
UA1614 type
na
26
Handset
mic
100
86.4
UA1614-4

 
 

United States Instruments (USI) Deck Talkers
Model #A-260 UA1614 (newer style model)
Ear Units


AC Impedance 
@ 1 kHz.
DC Resistance
(ohms)
750
64.7
750
64.7


Misc. Makers
Manufacturer
Misc. Makers
(will be updated soon)
Unit
Type
Element
Type
AC Impedance
@ 1 kHz.
Automatic Electric
DT
mic
14
"
DT
ear
600
"
DT
ear
610
SPC
Handset
ear / mic
310
"
Handset
ear / mic
260
"
Handset
ear / mic
310
"
Handset
ear / mic
265
Stromberg Carlson
DT
mic
120
"
DT
mic
95
"
Handset
ear
1100
"
Handset
mic
1900
"
Handset
ear
700
"
Handset
mic
1100
"
Handset
ear
250?
"
Handset
mic
900
Telephonics
Handset
ear
355
TMC (British)
DT
ear
200
TMC (Aussie)
DT
ear
145
Western Electric
DT
ear
650
"
DT
ear
655
"
Handset
mic
500
"
Handset
mic
300
       
Vintage Magnetic
   
 vintage measured as a pair in series
       
Western Electric
509W
vintage
23000 (23k)
Baldwin
Type C
vintage
20000 (20k)
Baldwin
Type C
vintage
20000 (20k)
DT = Deck Talkers
mic = microphone or transmitter unit
ear = receiver unit

Notes:

1)  All measurements were taken with element removed from housing and in free air.

2)  Warming up (or cooling down) the elements up can change impedance measurments.

3)  Any obstruction at all will change the impedance. Moving the obstruction (such as a finger) closer to the
     elements, will raise the impedance. At about 1/2" from the element it will start to drop again as you get
     closer  still.

4)  1kHz. frequency was used for these tests. Impedance will change as frequency changes.

5)  Some RCA handset elements have a capacitor built into the element. You need to remove that
     capacitor in order to use the element on a crystal radio. Most all other brands of Decktalkers and handsets
     (including the RCA decktalkers) have the capacitors on the out side of the element.




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