[R-390] Audio Gain Pots?

[Craig]

Hi Jacques,

Looking at the parts list in the Y2K R3; both R104 & R105 are 2.5K pots
2500 ohm, ± 20%, 2 W, JAN type RV4ATSA252D. In my Motorola, both are 2.5K
audio taper and the receivers works as advertised.

Now the "Too Loud Amelco" is a different animal for whatever reason (still
unknown). It appeared to be quite untouched/virgin upon my purchase. But it
had a 5K audio taper pot for the local gain & a 2.5K audio taper pot for the
line gain. To add more mystery the local gain pot which measured 5K was/is
audio taper; the case CTS was marked 2.5K!!!!! 

Standing 20 feet outside the radio shack with the local gain at zero, QSO's
could be heard very easily. Go figure? Swapped audio decks, IF deck's
between Motorola & Amelco and I still  had a "Too Loud Amelco". Checked
wiring cables, etc for shorts, grounds, opens and all were to the wiring
diagram. 

Used my "A" to "B" logic modifier (short piece of wire with alligator clips)
to make sure grounds were in fact grounded, Amelco was still too loud. 

In short; is was just easier to install 5K audio taper pots for both line &
local gain. The "Too Loud Amelco" now works as advertised. Gave up on the
cure and treated the symptoms.

YMMV,
Craig

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Jacques
Fortin
Sent: Tuesday, March 08, 2016 8:56 AM
To: 'Charles Steinmetz'; '390 list'
Subject: Re: [R-390] Audio Gain Pots?
Importance: High

Sorry to rain on the parade, but I just checked the pots I kept from two
R390A Moto "junk" units, and 2 are audio taper, the 2 others are linear.
Could it be that the Local Audio ones are audio taper and the line output
ones linear ?
The linear ones have CTS P/N 318K146 and the audio taper ones have 380 0588
009.
I have to check what's in my Motorola '56 now....

Regards to all,

Jacques, VE2JFE


Craig wrote:

>The line & local pots are both audio taper.
And you definitely do *not* want to replace them with linear pots, or you
will be the next one asking why the audio is screaming loud even with the
pot turned way down.



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