[R-390] Filters

[quartz55]

Yes, thanks for the replies.

A few things.

I've had these 2 R-390As for quite a while.  One of them is in fair shape, 
Dittmore, the front panel is a bit beat up and screwed with, but it worked 
pretty good when I got it, maybe 15 years ago.  I did some mainly cosmetic 
work on it and went through the book aligning it.  It's not a bad RX.  Sens 
is generally sub uV, with the IF module set up at 100uV input for -7V diode 
load.  I kind of disagree with Chuck(?) on the setup of the IF module.  I 
haven't been into the best input for it, but the book suggests 100-200uV 
for -7V diode load.  150 may be a good compromise but I need to check the 
intercept point for different inputs.

The second 390A had problems from the get go, EAC.  Bad PS chokes, bad 
filters (maybe) but the RF, PTO and PS decks are fine.  They both were 
converted to SS rectifiers, but I had a pair of 26Z5s I picked up a long 
time ago and one of the PS modules still had the sockets in place so I 
re-installed the tubes in that one.  I still installed a CL-90 in the AC 
input and have some 10W 220? resistors coming from Mouser which I think I 
will install in both because the voltages with the tubes is still a bit 
high.

Years ago I went through both RXs to clean out the mechanical dial mechanism 
and both of them are working very smoothly, and the PTOs are pretty close, 
stable and all xtals in the both RF decks are working.  Meters work in the 
EAC, Dittamore is missing the both meters, but I have some old stuff I'm 
going to try to get working.

Actually I had another 390A that I loaned out in 91, it was the best of the 
group, and the guy disappeared with it.  I never loan out radios any more. 
Same thing happened to an old HQ-145 I had.  The first good RX I had.

The IF modules, both EAC. I've been through both of them and the units 
appear to be undisturbed, no hacking in them, original solder joints.  One 
of them is reasonable (#5025), but I haven't checked out the AGC voltages 
and AGC response thoroughly.  All the filters seem to work and there is no 
great deviation of gain with any of them.  I have all the .1, .01, .033 caps 
on order to replace.  The filter blocking caps seem to have survived but 
I've already replaced them (only) with Orange Drops.  This module has gain 
problems however that appear to be not tube related by tube replacements.

The other IF (#123), seems to have a lot of problems.  .1, 1, 2KHz works but 
gain is much lower than the 8 and 16 KHz.  The 4 KHz seems dead, but I'm not 
convinced of that. 8 and 16KHz seem reasonable.  Resistance measurements on 
the filters are the same in the good module and the bad one, that's 
switching through the diff bandwidths.  The AGC is not working on the bad 
module either.  Unfortunately I got ahead of myself and replaced all the 
caps in the bad module with Orange Drops, so it's pretty crowded in there 
right now.  I ordered newer caps (Panasonic ECW radial style) because they 
are so much smaller plus they're 800V to put in the other module.

The 'good' module has a drifting gain issue that I'm working on.  The 'bad' 
module seems to have much better gain at least through the 8 and 16 KHz 
filters.  I'm thinking about pulling the  'bad' 4 and 2 KHz filters to go 
through the switching, it seems impossible to trouble shoot the switching 
with the filters in place unless someone can point me in another direction. 
It seems to screw with the AGC too.  I really don't want to send these 
things out, I enjoy working on them and have a fair shop and equipment to 
work on them.  Fluke 189, Analog Simpson 313-3, Motorola Service monitor 
R2005D/HS with LPRO-101 if needed, lots of other stuff.

So far the RF sections seem to be about equivalent, but I still have the 
better one (Dittmore) in the rack with most of the modules out of it to 
check out in the EAC.  I did have to pull apart T202 in the EAC RX to find a 
short in the transformer.  Never did really find it, but by moving around 
wires, it started working, so there must have been a short to ground that I 
got rid of.  It's really nice you can take these things apart and fix them 
down to the component level.

Bottom line, if anyone can steer me into not taking out the filters from the 
'bad' module, plus I really do not understand the AGC line going through 
R507 into the filters, but it somehow must end up on the grid of V502, but I 
don't understand the switching.  My thinking is the AGC is screwed up in 
that module because of the 'bad filter'.

Yes, these radios are incredible for the era they were build in, they seem 
to be right up there with anything build now, just not the bells and 
whistles and computer control.

My plan is if the filters are actually bad, I'll just use it in the 16KHz 
position with 'Dream' or similar IF decoder mixed down to sound card 
capability if I can get the AGC to work.

I've read through a lot of the R290A FAQ pages, so it's not like I haven't 
been doing my homework, it just gets a bit long to read these old threads 
that seem to repeat themselves and pull out the gems.

Sorry to be so long winded.

Dave
N3DT