[R-390] Too Loud Amelco is Dead: Long Live the Amelco

[Larry H]

Hi Craig,  I just went through this same problem and part of mine was as you determined - bad audio pots. I was able to find a good original and that fixed most of my problem.  But, there's more - mine had a short to ground in the RF deck on one of the secondary antenna xformers thus eliminating agc to the RF amp.  I easily determined this by measuring the agc at the antenna trimmer cap shaft gear (not the shaft that sticks through the front panel, the one it mates to).  Or at E208, E210, and E211 if your careful about loading.  It should measure about 80% of the agc voltage.

Regards, Larry


On Thursday, June 26, 2014 3:44 PM, Raymond Cote <bluegrassdakine at hotmail.com> wrote:
 


Was that MCM?

Sent from my outdated iPhone wireless thingy

> On Jun 26, 2014, at 15:46, "Craig Heaton" <hamfish at efn.org> wrote:
> 
> To All,
> 
> It’s time to report my findings. First a little flash back to refresh
> memories. I believe this R-390/A followed me home sometime in February 2007.
> It went thru the usual recap & etc. After a good alignment or two the loud
> audio from either the line or local gain became obvious. Loud audio is
> better than no audio, thus the issue was pushed down the list of thing to
> do. I’d get to it……….mostly on rainy days in Oregon.
> 
> In the past several years everything has been tried many if not dozens of
> times. Tubes were swapped, old tubes replaced with NOS tubes from the junk
> box, tube voltages measured &  compared with a good (to me) Motorola
> R-390/A, IF decks swapped, AF decks swapped, C603’s swapped, another set of
> caps for C603, different speakers, different matching transformers between
> the receiver & speakers. The wiring harness was checked for shorts, opens,
> and grounds. Every wire between the IF going to the AF deck was checked. All
> the plugs/wiring coming or going to the AF deck was checked. Even back
> shells of the plugs were unfastened to look for issues, nada. At this point
> in time I can proudly say all was tried that I could think of, or read.
> 
> The problem, cause, or whatever was on the panel; front or back of the
> Amelco. Both R104 & R105 were good and within spec of 20%. I had a few more
> in the junk box. So I picked the two with the greatest resistance and tried
> them, nada once more. 
> 
> Art Collins please forgive me, I have sinned. R-390/A lovers, you read it
> here first. Both 2.5K potentiometers for R104 & R105 have been replaced with
> 5K audio taper pots. Life is now good. When the phone rings, just turn down
> the local gain. Did I treat the symptoms or find the cause. Darned if I
> care, it works. At the min setting on local gain, audio from the speaker is
> almost gone. One has to listen closely to hear the little sound coming out.
> At a setting of 1 to 1-1/2 the audio is comfortable. Crank the local gain up
> and that ½ watt of audio power rocks the speaker. 
> 
> 73’s
> WD8KDG
> Craig
> 
> PS: ? By the way, the 5K RV4 pots were found on a new internet surplus
> website. Ten bucks a pop and they have 2.5K audio taper pots for that price!
> 
> 
> 
> 
> 
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