Mark – I have a nice MD-7 with some mating connectors. 73 – Mike
Mike B. Feher, N4FS
908-902-3831
From: milsurplus-bounces@mailman.qth.net <milsurplus-bounces@mailman.qth.net> On Behalf Of Mark K3MSB via Milsurplus
Sent: Monday, August 3, 2026 10:54 AM
To: ARC5 <arc5@mailman.qth.net>; List Milsurplus <milsurplus@mailman.qth.net>; Military Radio Collectors Association (mrca@mailman.qth.net) <mrca@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