The RF deck is out of the equation, I'm feeding the IF strip only with 455.  Yes, I have caps coming, and I've switched tubes with an IF module that does not do it, no change.  I've got some tube extenders and I need to start checking the voltages on the tubes as it happens.  Trouble is it only does it for about a half hour, then I have to let things cool off to start over.  I suppose I could lay out the IF strip with the RX on it's side and start shooting freeze spray on things.  It may come to this.

OK, I got this program called 'Dream' which is a DRM decoder for the soundcard, also AM, SSB, CW with variable bandwidths, etc.  You can input an IF (like out of an R-390) once it's been mixed down to what your soundcard can take, like 12KHz.

Trouble is I hear the input as well as the output at the same time.  How do I turn off the input monitor so I only hear the output?  Seems I've been able to do this in the past but forgotten how.  Using an SB Audigy 4.

N3DT

There's an R390 forum on QTH?  Link please, I couldn't find it.

Thanks for the link, I'll check it out.

I have the receiver in MGC.  That's the way it's tested through the IF amp, but I'm not saying it couldn't be a similar issue.  It's just curious that when it 'snaps' the gain goes way up, but then it slowly goes down to wander around for a while and finally settles somewhere in the middle after a half hour or so.  It sure acts like a tube, but undoubtedly it's a cap somewhere, maybe.  I haven't replaced them yet, it's on the list.  I'm getting a list up for mouser to order.

I haven't messed with the other IF strip, it has bad mechanical filters, but I've replaced the caps in it.  I'll try it next.

It's also curious that the loss through different filters seem to change with time too, I suppose the loss through the filters could change with temp.  I need to get the freeze spray out, but not on the tubes.

The IF section gain wanders around from 100uV to 700uV input for the same output.  Not long after turning the radio on, it 'clicks' and then the sensitivity jumps way up (less uV for same output).  Then as it warms up it wanders around.  I've swapped the tubes and that doesn't make any difference.  Ideas?  I'm watching the output on a VM measuring the diode load, but I can also hear the noise go up and down with the diode load output.

Also does anyone know of an R390A specific forum or site?  I found the R390A FAQ site, but there is no forum there that I see.

I rewound an old 90V 300W transformer to give me a 20A 13V power supply, so I too have dug into these old transformers.  I just may whack apart one of these chokes to see if I can re-wind them, but they may be potted, not sure until I get one apart.  They're sealed, like the Freed transformers, but maybe I can heat it up and get it apart.  Nothing ventured, nothing gained.

Well, I guess I'll just have to make a converter.  Maybe I can find a xtal that will convert 455 down to somewhere in my SB card.  I did download Dream and fed some audio into the SB card, but I couldn't figure out how to shut off the input monitor, so I was getting the input and output monitoring at the same time, kinda confusing to say the least.  I've got some old MCL mixers that would probably work and might be easier than finding all the components to make a converter, actually I could just feed my Service Monitor into the MCL and feed the mixed output into the SB.  Hmmm.  Yeah, I'd like to hear that DRM.  I'll have to check out the Sound Forge too.

I've got the sensitivity of the R390A down to less than 1uV on most bands now.  I just need to get the AGC working better and I found a bad T202 which affects 1-3MHz, but I think I've got it working again.

I kind of figured it'd be on the output of the IF strip, but where is the plan for it, like a schematic or something?  I hate re-inventing things if it's already done.

Actually I think what is making the ripple is mostly the chokes which are about 1/2 the DC resistance they should be, which is probably indicative of shorted turns.  With a much lower value of H, the PS filter will look more like a capacitive input filter which raises the voltage, and also probably makes for more ripple, but given that both of the high current chokes are bad, I really can't do much until they get replaced one way or the other.  I can get new Hammond ones in the range for about $70 for all 3.  The capacitors are all new and they check out.

The AF module with all 3 good chokes is working pretty good now.

So where is the 455 to 12 converter?

I don't think the main PS transformer was a weak link. Been my reading that it hardly ever goes bad.

Yeah, I've got my eye on a Hammond, 4H 250ma.  I'm sure it would do for the 2 large ones.  $25 ea.  Looking on ebay these guys want $45 and up to well over $100 for some old junk.

I was looking for a power transformer too, the ebay ones are out of sight for either old or used stuff, I found a nice new Hammond one for $88.  Fair Radio has an R390A transformer for a reasonable price too.  It was too low in the voltage department for my use.

The chokes are on the AF module.  The filters are on the IF module.  Luckily Murhpy hasn't got me there, the bad filters are on the funky IF module, the good filters are on the better IF module.

Trouble is I lent a perfectly good (the best one I had) R390A to someone that took off with it and I've never seen it again.  Some people....

After much digging around I think I've got it figured out, if anyone cares.  Looks like in the 2 AF modules, which include the 3 chokes for the PS, I have 3 good chokes and 3 bad chokes.  One of the bad chokes is actually swollen up.  So I've installed the 3 good chokes on one module.  I found the DC resistance values of the chokes in the book as well as printed right on the choke. The module that has the bad input choke (low resistance) turns the PS into effectively a capacitive input filter which in operation gives a higher output voltage.  So it looks like to make the other receiver work properly, I need at least 2 new chokes for the IF/RF B+ and another for the AF B+ if I want to use the AF section.  It may take a while to find these items even if I wanted to afford them.  All I can do is keep a look out on ebay and several of the places that sell items like this (Fair Radio Sales).

Anyhow, I'm on to the IF sections.  They both seem to work to some degree or another, trouble is, one of them has some bad mechanical filters.

I've been playing with these 2 audio modules and the best one still has some slight hum to it.  The other one needs some tubes which I have, but I still have very high P-P voltage on the output of the rectifier, even with the rectifier tubes.  The tubes dropped the DC voltage about 20V.  Only thing I can figure is some of the chokes are bad.  I may try replacing the best ones into the good module.  I'm not going to destroy it, and chokes are rather expensive, if available at all, so my thinking is I'm just going to remove the tubes from the audio sections and install a LM380 type audio chip and rectify the 6.3 for the filaments to supply the chip.  But I'm not going to make anything non-reversible in case someone wants to put it back in original configuration.  It's just not worth it for me to spend that kind of money on this thing as long as I can get the RF and IF sections working good.

As far as the IF/RF B+ chokes I may see what I can do with another type filter, or I may spring for a new after market choke for the one that's bad.

I did try to measure the Henrys with the Impedance Bridge, but it didn't report very good results, much less than 10 Henrys and one is supposed to be 6 and the other is 2.5-12.5H, but then I was feeding them 1000Hz, not 60Hz and the reactance at 1000 could be way off.  The bridge did seem to measure capacitance pretty good.  I can feed the bridge with an external generator and I may try that.

I'm going to post a new thread to see what I should be seeing as far as P-P ripple on the outputs of the power supply.  I haven't seen that listed anywhere that I can remember.