[R-390] A "baby" R-390A

[John Kolb]

On Sat, 5 Oct 2002, Philip B Atchley wrote:

> Hello All.
> A gentleman just dropped off an R-648/ARR41 receiver for repair.  This
> aircraft receiver appears to be very similar to out "pets", the R-390A.
> But it is much lighter, smaller and has a somewhat different
> layout/circuit scheme.
>
> He said it has poor audio on AM and expressed concern that he "hoped" it
> wasn't the 6kHz Crystal filter.

Well, it's a Collins mechanical filter, not a crystal filter.
I wouldn't suspect the filter is the problem unless it has
a very high insersion loss. If the signal levels are the same
in AM mode and CW/FSK (1.4 kHz filter, it's probably OK, although
the parts unit I once bought had both filters bad). I can supply
you with a replacement filter (F500Y60, smaller Y case filter)
if you should turn out to need it.

Leaky coupling caps in the audio stage would be most likely
if the signal sounds distorted rather than weak.

>
> Anybody out there worked on these?  Does it have any "pitfalls" or other
> things that I should be aware of before "digging in"?
>
If running with the dynamotor power supply, you'll need 27.5V
a 3A if above 32 deg F, or 5.8A if below. Starting surge of 20A.
Too low a primary supply could cause problems, I suppose.

If the dynamoter was replaced with an internal homebrew supply
you might check out the entire conversion, as these often
involved rewiring the filiment string for 6.3 or 12.V v
transformer windings.

I have a rather poor manual copy here if the owner didn't supply
one and you can't find one posted on line (NAVAIR
16-30ARR41-502)

John

> 73 de Phil  KO6BB