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

[Mark K3MSB]

I do too Mike!

On Mon, Aug 3, 2026 at 11:59 AM Mike Feher <n4fs at eozinc.com> wrote:

> Mark – I have a nice MD-7 with some mating connectors. 73 – Mike
>
>
>
> Mike B. Feher, N4FS
>
> 89 Arnold Blvd.
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> Howell NJ 07731
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> 908-902-3831
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>
>
> *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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