[R-390] R-390A IF deck caps in T501 or T502
Barry
n4buq at knology.net
Wed Jan 23 17:39:21 EST 2019
That's a logical assumption and good fix (and I presume Roger R. would say they didn't rely on cap checkers either...).
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Larry H" <larry41gm at gmail.com>
> To: "R-390 Forum" <r-390 at mailman.qth.net>
> Sent: Wednesday, January 23, 2019 4:22:45 PM
> Subject: Re: [R-390] R-390A IF deck caps in T501 or T502
>
> Dave, it was more of a process of elimination. After determining that the
> 2nd stage gain was erratic, I started with the tube, then the bypass caps.
> Then the voltages on the tube. Then the output transformer, so I checked
> to see if the 2 slugs were still at their peak. One was and the other not,
> and it would not peak. I measured the coil resistance and examined it for
> damage and loose wires. All ok there, so it had to be the caps. Since I
> don't have a cap checker, I removed both. This is one time I wish I had an
> accurate cap checker, then I would have checked the mica first. Replacing
> both confirmed one of them was bad. Reinstalling the ceramic with a new
> 200 pf mica confirmed it was the mica.
>
> Regards, Larry
>
> On Wed, Jan 23, 2019 at 7:51 AM dog <agfa at hughes.net> wrote:
>
> > I mean the bad ones, how did you determine they were bad?
> >
> > On 1/23/2019 07:23, Larry H wrote:
> > > Dave, I tested the new cap only for leakage at the rated voltage (500 v)
> > > before installation. After installation, for correct operation during
> > warm
> > > up.
> > >
> > > Regards, Larry
> > >
> > > On Tue, Jan 22, 2019 at 12:09 PM dog <agfa at hughes.net> wrote:
> > >
> > >> Larry, how did you test the 200pf caps? Did you test the actual cap? I
> > >> haven't replaced mine yet, procrastinating.
> > >>
> > >> Dave N3DT
> > >>
> > >> On 1/22/2019 00:14, Larry H wrote:
> > >>> I received the 200 pf caps today that I ordered from Just Radios. I
> > put
> > >>> the original 39 pf cap (with -30 tempco) back in, that I had removed,
> > and
> > >>> installed the new 200 pf. It's working great. IF warm up shows very
> > >>> little drift and good stability. The size is very good for good fit
> > with
> > >>> ample room in T501. Both coils peak with ample tuning on both sides.
> > >>>
> > >>> Regards, Larry
> > >>>
> > >>>
> > >>> On Wed, Jan 16, 2019 at 1:20 PM Larry H <larry41gm at gmail.com> wrote:
> > >>>
> > >>>> Hi Dave, Sorry your posts are not getting through.
> > >>>>
> > >>>> The 5% are fine as long as it will peak on adjustment, which it
> > should.
> > >>>> Does 1 or both coils not peak in yours? The easiest way to check is
> > to
> > >> rx
> > >>>> in cal, tune to signal, measure dc on diode load.
> > >>>>
> > >>>> Regards, Larry
> > >>>>
> > >>>> On Wed, Jan 16, 2019 at 7:20 AM dog <agfa at hughes.net> wrote:
> > >>>>
> > >>>>> Larry,
> > >>>>>
> > >>>>> For some reason my replies to the 390 list are not getting through. I
> > >>>>> might have to re-register, don't know. Anyhow, I've been having the
> > >> same
> > >>>>> gain problem. I traced the jump in gain to T502 after much fiddling,
> > >> but
> > >>>>> didn't get much farther, I sorta got burned out just finding that. I
> > >> had a
> > >>>>> thread on it last summer. I have a bunch of dipped SM caps but
> > they're
> > >> 5%.
> > >>>>> Is it that important they be 2%? I thought that was what the
> > >> adjustment in
> > >>>>> the coil is for? Oh, I see I've got a 200pf 5% 500V one. I may have
> > >>>>> another if I look through the pile. Most of what I have are 270pf.
> > The
> > >> 200
> > >>>>> is fairly small too, only 3/8" at the widest.
> > >>>>>
> > >>>>> Dave N3DT
> > >>>>> On 1/16/2019 00:02, Larry H wrote:
> > >>>>>
> > >>>>> Still Holding. I ordered 20 of the 200 pf from justradios. Hope
> > >> they get
> > >>>>> here soon.
> > >>>>>
> > >>>>> Tomorrow I celebrate with Kielbasa and cold brewsky.
> > >>>>>
> > >>>>> Regards, Larry
> > >>>>>
> > >>>>> On Tue, Jan 15, 2019 at 6:21 PM Tisha Hayes <tisha.hayes at gmail.com>
> > <
> > >> tisha.hayes at gmail.com> wrote:
> > >>>>>
> > >>>>> Yea, at the prices for mica caps you definitely do not want to be
> > >>>>> shotgunning the replacements of those things through the deck.
> > >>>>>
> > >>>>> *Ms. Tisha Hayes, AA4HA*
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