[R-390] Receiver noise

[dog]

R390A model. Yes, I don't have a load on the balanced input. I see in 
the manual they use a load. IF gain has been set using the book method 
and also the other Line Level method, but no load on the antenna port, 
I've been told both things, load or no load. My sig gen is a 50Ω output 
Moto service monitor 2005D. There's not a whole bunch of difference 
between the two methods, but it does seem like the gain is hot. I do 
notice the 14MHz band seems a bit lower in noise than the rest but it 
still meets the sensitivity test easily. Is that mostly a function of 
the band crystal oscillator? I only have another set of tubes for 
another 390A but they are all suspect as well as a few spares. I have no 
way to test other than substitution. Everything in these radios is 
pretty much original or replaced with original parts, no SSB mods and 
the like. Still using the tube rectifiers. Caps replaced in the PS as 
well as the RF and IF sections. Listening to it over the air it sounds 
fine. I'm actually trying to sell it. It's got all the panels, meters 
and all. Front panel is a bit rough is all. In the past I went through 
it and did a complete tune on all the circuits.

Dave N3DT


On 10/9/2018 14:03, Roy Morgan wrote:
>
>> On Oct 9, 2018, at 10:15 AM, dog <agfa at hughes.net 
>> <mailto:agfa at hughes.net>> wrote:
>>
>> When I don't have an antenna on the balanced (or unbalanced) inputs, 
>> the noise level is quite low on the RX. ... I can hear the rx 
>> internal noise with no antenna, and when I attach an antenna, I hear 
>> an increase but nothing like the R390A. Is this typical?
>
> Is this an R-390/URR (the non-A)? (That should not matter it seems to me.)
>
> Have you set the IF gain?  On an R-390A, it is often found that the IF 
> gain needs to be adjusted. The procedure is simple, though I don’t 
> remember the details.   I would put a resistor on the input (125 ohms 
> on balanced input), no antenna, gains all the way up, and set the IF 
> gain pot for modest noise - a low level on the line output meter. 
>  (AGC on or off should not make a difference.). Then see if most bands 
> give the same amount of noise.
>
> You might want to do a rough sensitivity check if you have a signal 
> generator.  Note that the calibrator signal is introduced at the very 
> first stage of the radio, and gives a quick rough check of overall 
> sensitivity.
>
> Also you may want to go through the set with known good spare tubes 
> one at a time, replacing the original at each step, to see if you have 
> a weak tube.
>
> Roy
>
>
> Roy Morgan
> k1lky68 at gmail.com <mailto:k1lky68 at gmail.com>
>
>
>