[R-390] the saga cont. part 3

[Flowertime01 at wmconnect.com]

Brian,

You wrote, feed the unbal ant in 

At the antenna relay, couple one of the balanced antenna cables over to the 
unbal jack. Either P207 or P206 over to P205. And then just ground the 
other balanced input by sticking a wire in the J104 connector on the back panel.

When you use the unbal input with wire P205 you skip the whole front can of 
tuning coils and caps. The unbal input is thus a whole lot wider in 
response than the balanced input. You thus get a lot more signals and noise into 
the RF tube and thus a lot more intermodulation. It makes not a lot of 
difference when you use a signal generator except the front slug and cap will not 
align correctly in each of the Octaves. You have likely discovered the front 
cap on each of the cans still does not appear to have any tuning effect even 
if you do use the balanced input. This is true expected operation. There is 
a procedure to get that front cap properly adjusted. It will not increase 
the signal level. On the signal generator you can not measure the difference. 
It does help cull out unwanted signals when you have an antenna hooked up. 

-----------
Anyone care to comment on similarities and differences between the HQ-129's
single-crystal filter and the 390A's?  I note the 390A has no "phasing"
control on the front panel...

Are you trying to compare the HQ-129' to the mechanical filters of the 
R390/A or to the 455 Khz .1 KHz band pass filter?

The 455 KHz .1 Khz crystal has C520 on top of Z501 can and it does get 
adjusted.
The trimmer caps on the mechanical filters do not shift the bandpass of the 
mechanical filters. These caps match impedance and thus signal level 
through the filters. We just trim them for all we can get. But the plan was to 
trim them so the signal would be equal through each of the filters. You were 
supposed to balance the levels as you changed bandwidth.

Mechanical filters are in fact mechanical. Or more mechanical than 
crystals. The side skirts of the mechanical filters are much steeper than RC 
filters. Not better than a crystal. But the mechanical filter has a wider band pass 
than the crystal. Observe the single 455 KHz .1 KHz band pass of the R390 
crystal and the 2 KHz bandpass of the mechanical filter. Consider the 16 Khz 
mechanical filter. How many crystals do you need to produce a 16 KHz band 
pass with a crystal filter. Try to sort out AM stations at night without the 
selective IF of either the R390 or R390/A. You do need some form of 
selectivity in a good DX receiver.

You have reached 10 :1 and 3 UV sensitivity. Great. You now have a working 
R390/A.

Time to put some work in it and get it up to 20:1 and push the sensitivity 
toward 2 UV or better. This is all in tube selection and more passes through 
the alignment. But if you do not have tubes on hand. Be happy and use the 
receiver as is. 10:1 is good and enjoy. Buying new tubes may not help. I have 
often brought brand new name brand tubes and had then be more noisy than 
the tubes I have on hand. Just spending money is not a sure solution.

For real let the receiver run 24 x 7 for a couple weeks (turn it off it its 
going to rain, no reason to lose it to a lighting strike in the 
neighborhood). It will help the electrolytic caps and may quite some of the tube noise 
down. Spin the knobs and switches to help keep the oxide off the contacts 
and work the lube through the gear train.

Good Job happy you have endured all the frustration.

Roger AI4NI</HTML>