[R-390] Tracking down low sensitivity 0 to 8 mhz problem

[Larry H]

Hi Jordan, Good work testing and documenting your problem.  Glad the 1 MOhm
isolation res worked out.  It looks like the 1st var IF is the key to this
problem.  I'd focus on fixing the tracking and examine the 3 tuning cans -
take them all out and apart and examine them.  Make sure that the 3
trimmers peak correctly.  I've had numerous problems with the 5 SM caps in
the 1st mixer plate circuit.  Also check bypass C280.

Regards, Larry

On Sun, Apr 14, 2024 at 7:28 AM Jordan Arndt <Outposter30 at shaw.ca> wrote:

> Hi Bob...
>
> Yes, I have an Ailtech 460 sig-gen, and yes, none of the bands are totally
> dead.
>
> To check the sensitivity, I use the sig-gen at 50uV and again at 1uV, in
> AM
> mode with 400hz modulated at 30%. I also use the Carrier Level meter
> and/or
> the Line Level meter accordingly.
> I also check to see if I can peak the internal tube noise by adjusting the
> Ant Trim and checking for a peak in the noise as indicated on the Line
> Level
> meter with the receiver input terminated in a 50 ohm load.
>
> Wth a 50uV input signal, the Carrier Meter shows a drop off below 8Mhz of
> ~
> 4 to 6dB per band, with the 3 Mhz band being the outlier showing a ~ 12dB
> drop which I believe is due to a weak crystal which produces only 2.4Vdc
> at
> E-402. The rest of the lower band crystals all meet the -4 to -11Vdc spec
> as
> measured at E-402.
>
> Aside from a minor tracking problem in one of the 1st variable IF
> transformers, the rest of the RF xfrmrs appear to be working normally and
> track properly. I do note some scratching when the Ant Trim is rotated
> quickly, but that only appears with no antenna connected. The Ant Trim
> peaks
> normally on all bands.
>
> I hope this answers some of your questions...
>
> 73...Jordan VE6ZT
>