[MRCA] [Milsurplus] AN/ARC-5 MD-7 Tone Oscillator Transformer

[Mike Feher]

Mark – I have a nice MD-7 with some mating connectors. 73 – Mike 

 

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

908-902-3831

 

From: milsurplus-bounces at mailman.qth.net <milsurplus-bounces at mailman.qth.net> On Behalf Of Mark K3MSB via Milsurplus
Sent: Monday, August 3, 2026 10:54 AM
To: ARC5 <arc5 at mailman.qth.net>; List Milsurplus <milsurplus at mailman.qth.net>; Military Radio Collectors Association (mrca at mailman.qth.net) <mrca at mailman.qth.net>
Subject: [Milsurplus] AN/ARC-5 MD-7 Tone Oscillator Transformer

 

I acquired some spare parts for my MD-7 including all three transformers.  

 

Two of the three checked out according to the manual.   The tone oscillator transformer T-57 may have an issue.

 

The manual says the resistance between pins 1 and 2 (case) should be between 58-75 ohms.

I measure 5 ohms.

I measure the inductance between pins 2 and 4 to be 0.28H, and that's within the range specified in the manual.

I'm wondering if the spec for the resistance between pins 1 and 2 is wrong in my manual?

My manual is AN 16-30ARC5-2 15 Dec 1954

If you have a different version of the manual, can you please check the specs for T-57?
The info is in Table 7.2 in my version of the manual.

The manual gives no other resistance measurements for the primary.  I measure:
1-2:  5 ohms
2-3:  30 ohms
3-4:  34 ohms.

Even if the 5 ohms is a bad value, this should not impact the operation of the Tone Oscillator.

 

I might be able to just add a series resistance between pin 1 and the connected switch.

 

73 Mark K3MSB

 



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