[AMRadio] Collins R390/URR versus R390A


Brett Gazdzinski Brett.Gazdzinski at verizon.net
Sat Mar 22 21:44:21 EST 2008


It arrived Friday.
It had very high distortion, and low sensitivity.
 I found a bad 1st mixer tube by doing voltage checks at the
tube sockets.
I also found the wrong tube in the 3rd IF amp, which improved
the sensitivity a lot once a 6ba6 was installed.

With a good speaker hooked up, it does not sound real bad, but there
is no low end below about 200 Hz.

It also has quite a bit of noise, antenna shorted, but, I notice I
could pick up signals on 80 meters well, without any antenna
connected at all!
Pulling the RF amp tube removes 70% of the noise.

Tuning is off between some bands, close on 80 meters, off a bit on 40,
and the selectivity is not great under poor conditions, the rig needs
a good filter.  I wonder if it could be moved to 455 KHz...

Its in quite good shape, but needs a good cleaning, no mods that I can see,
everything seems to work ok, no bad parts so far except the tubes I found.

Its performance is far below the homebrew receivers, fidelity is low, noise 
is high,
tuning is sloppy, the bfo is weak, filtering is poor, and frequency accuracy 
is bad.

I am going to see if I can fix some of these problems.

One thing I really don't understand is all the complex stuff going on with 
the agc
setup. The homebrew receivers work better in that department without any 
sort
of agc amplifier and elaborate bias tricks the R388 uses.

Brett
N2DTS






----- Original Message ----- 
From: "Jim Wilhite" <w5jo at brightok.net>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>
Sent: Friday, March 14, 2008 7:55 PM
Subject: Re: [AMRadio] Collins R390/URR versus R390A


> Pretty good receiver Brett.  The audio with a good speaker is better than 
> most Collins I have heard.  The rest of the mystic Collins accolades apply 
> to it.  Watch out for bad bypass caps in the front end.
>
> It is a wrist buster, but not as bad as the 390 or 390A.
>
> Have fun and live it up.
>
> Jim/W5JO
>
> ----- Original Message ----- 
> From: "Brett Gazdzinski" <Brett.Gazdzinski at verizon.net>
>
>
>
>>I have an R388 on the way.
>> Should be fun to play with....
>>
>> Brett
>> N2DTS
>
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