[R-390] Gain drift

[Larry H]

Dave, Great work!  The IF alignment procedure is in the y2kr3 tech ref
chapter 6, here's the link:

http://www.r-390a.net/Y2K-R3/06_Chapt_06.pdf

Regards, Larry

On Sat, Oct 20, 2018 at 1:58 PM dog <agfa at hughes.net> wrote:

> Jacques,
>
> Yes, those T502 resistors are still in there. So far I haven't heard the
> gain drift since I resoldered the joints but I need to give it some
> hours. I also replaced the detector tube for the noise and it didn't do
> anything, tried the Limiter V507 and that may have done it. I need to
> give it some time now.
>
> T502 can looked from the top like it had been messed with. Inside it
> appeared that the input circuit had been tampered with, but what looks
> like original parts. I took a big iron, heated it up good, used a little
> rosin solder paste and re-tinned the joints. That's all I did. They did
> look a little cold. I doubt the joints were original.
>
> I notice the tuning on T502 changes with different tubes? I was looking
> in my Navships book for the tuning of the transformers in the IF stage
> but can't find it. Anyone know where that is? I thought I'd been through
> that years ago. I know I did the first variable IF and I seem to
> remember going through the IF.
>
> Dave N3DT
>
>
> On 10/20/2018 14:11, Jacques Fortin wrote:
> > Dave, speaking about the "funky solder joints" in T502...
> > Does someone previously removed the internal damping resistors within ?
> > Meaning R553 and R554 that can be seen in the schematic ?
> > Both are 47k ohms, 5%, 1/2W.
> > R511 and R512 in T501 are the same (and should be present also !).
> >
> > Removal of those resistors was a "modification" recommended by some
> people
> > 30 years ago !
> > But the end effect was - in some cases- self-oscillation of the IF
> stages.
> > Like having a regenerative receiver within the IF strip...
> > No wonder then if the gain is very high at turn-on and the global
> operation
> > unstable.
> >
> > Have a check !
> >
> > 73, Jacques, VE2JFE
> >
> >
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>