[R-390] R-390 Non-A module interchangeability

[Bill Hawkins]

Don't think the power supplies are different.

There was an early field change that modified the power supply,
and made unmodified power supplies incompatible.

IIRC, the mod brought out the B+ return (lifting it from ground
in the PS) using the wire for 24 VDC that was used for the really
rare 24 volt power supplies. Rare because the dynamotor or
thyratrons made too much noise, reducing sensitivity.

The mod also involved the B+ fuse on the chassis somehow.

Bill Hawkins


-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Paul Anderson
Sent: Thursday, February 04, 2010 12:19 PM
To: Norm Drechsel
Cc: r-390 at mailman.qth.net
Subject: Re: [R-390] R-390 Non-A module interchangeability

Norm,

>From what I understand, the IF and AF strips in R-389/R-390/R-391 are
all interchangeable.

Power supplies, although the same part # and external appearance are
the same from R-390/R-391 but different in the R-389.

I have one such power supply (R-389 wiring), but I don't recall the
exact differences - they do sound like what you describe from hazy
memory.  It tests as a non-working PS in my R-390 as you discovered.

This can be confirmed by checking the first chapter of the R-389
manual, I believe, where they list module compatibility with the
others in the series.

As far as I recall, there is no external means of checking the
difference - no MOD code, no nothing... you have to know what the
wiring is, and check it.

My guess is that the wiring change you have reflects this variation,
and that at some point one of your R-390's got modified to accept an
R-389 power supply (which you appear to have one of on hand).  It is
also possible some production R-390 units were originally wired that
way, but that is a pure guess.

Paul

On Tue, Feb 2, 2010 at 12:42 PM, Norm Drechsel <norm at wa3key.com> wrote:
> I have two R-390 Non-A's, one of which I'm in the process of
> restoring.  My question concerns the interchangability of modules
> in the Non-A.  I'm used to the R-390A, where all makes and
> contracts seem compatible - but even though my two radios are both
> Motorolas from the same 14214-PH-51-93 contract (s/n 4127 & 4895)
> I've discovered major differences in the power supply module
> connector.  Among others I've yet to trace is the B+ center-tap that
> goes to ground via the 3/8A fuse is on pin 12 in s/n 4127 and pin
> 15 on 4895.  I have three power supplies, only one of which is
> compatible with the radio I'm restoring.
>
> Has anyone documented these differences?  And if so, are other
> modules involved besides the power supply?  The last thing I want
> is to smoke a module when testing.
>
> I receive these posts in digest form, so there may be a delay in
> my response.
>
> Thanks.
>
> 73 de Norm - WA3KEY
> norm at wa3key.com
>