[R-390] 1st IF tracking problem solved

[David Wise]

It can't have been the repair.  Glue joints don't matter - as long as the usual amount of iron is in the usual place, all is well.  I predict the slug is the wrong material, dot notwithstanding.  If you have an LCR meter or a grid dip meter you can check this by winding wire around two slugs and comparing their L.

IMHO,
Dave Wise
SWL in Hillsboro Oregon (inactive)

From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On Behalf Of Jordan Arndt
Sent: Thursday, January 27, 2022 10:58 AM
To: Collins R-390 HF Receiver List <r-390 at mailman.qth.net>
Subject: [R-390] 1st IF tracking problem solved

Hi again group...

In going through this '60 SW, I had noticed a 1st IF tracking problem, causing a serious roll-off in the gain as I tuned upward through the 7 mhz band. During alignment, the core in L213-1 ended up having to be adjusted almost to the end of the threading above the 1st IF rack at the 1.250 mhz alignment point, far above the other 2 1st IF slugs.

While I could peak the variable cap in that transformer at 7.250 Mhz, I could still increase the gain by pulling that end of the slug even higher.

Since I had to replace a number of fixed SM caps in the xtal oscillator, and attend to some other concerns, when I last pulled the RF deck, I replaced the SM caps across the 1st IF cores which are under the deck, while I had access to the underside components.

While the rest of the work was highly successful, I still found a problem with the 1st IF tracking, in particular the same slug in L213-1. In fact, the farther I pulled the rack upwards the stronger the signal would get when on the 7 mhz band, while it peaked properly at the 1.250 alignment setting.

This morning, I swapped out that entire rack with one from a working 390a, and not only did it restore proper tracking, after alignment the sensitivity on all the lower bands improved, especially above 6 Mhz. The slugs are now very close in ajdustment height.

It had to be that slug, which had always appeared to be fine, and had the appropriate green dot.

However, I put it under some magnification and found a hairline crack around the entire circumference of the slug about 1/4 ich from the bottom of the slug, which upon even closer inspection, turned out to be a very well done repair of a broken slug.

I myself have repaired broken slugs before using "crazy glue" or similar, and never had a problem with those repaired slugs. Then I realized that all the those repairs were on slugs in the RF racks, never the IF racks.

Another lesson learned in bringing this thing back from the dead...!

73...Jordan VE6ZT



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