[NJARC] Radio Debugging PS
John Ruccolo
jr6v6gt at yahoo.com
Fri Mar 7 14:30:51 EST 2008
Scott,
That was a typo in my previous email -- I meant 22 at
450V, not 22 at 250. But I think you understood that.
Anyway, Mouser does not list 16/450V (but I'm sure
*somebody* makes 'em) so I'm glad you put in what you
have.
You have discovered the *tremendous* diefference in
size between old, wet elecrolytics and modern dry
electrolytics. Materials science, etc. has advanced a
LOT in the last 70 years! ;-)
Al said it better than I did -- the voltages you
measure will *not* be exactly what Halli. measured,
and you'll drive yourself crazy trying to achieve
that. You're looking for +/- 5% or so. Even +/- 10% is
OK in most cases. You seem to be well within range on
most voltages.
You did a very smart thing, BTW, by cranking back the
AC line voltage before taking measurements.
Your DVM is fine, and WAY, WAY better than whatever
Halli. used to measure voltages 70 years ago. You can
worry about getting a VTVM another time. There are
plenty of them around, and they are cheap.
Didn't you say you recently got an RF generator? Fine
-- now is good time to start playing with it. Set it
to say, 1,000 Khz and tune the receiver to that
frequency (middle of the BC band). What happens? You
can connect the generator straight to the antenna
screw. Keep the output of the generator cut back at
first, until you figure out how sensitive the set is.
I assume you're using headphones, since you don't have
a speaker connected?
If you don't yet have an RF gen. than hook up the
antenna and see how the radio behaves.
I'm glad you're enjoying the learning process.
Regards,
JR
--- Al Klase <al at ar88.net> wrote:
> Visit our web site - See http://www.njarc.org
> _______________________________________________
> Close enough for government work! - Al
>
> Scott Roberts wrote:
> > Visit our web site - See http://www.njarc.org
> > _______________________________________________
> > The schematic shows it going through cap
> C-40(10mfd electrolytic)
> > parallel with resistor R-25(950 ohm) then to
> ground as you said.
> >
> > Is there any problem with it showing +5.86vdc?
> >
> > Scott
> >
> >
> > --- Al Klase <al at ar88.net> wrote:
> >
> >
> >> Visit our web site - See http://www.njarc.org
> >> _______________________________________________
> >> The 6R7. pin 8 thing has got to be an error in
> the
> >> documentation. This
> >> is the cathode of the triode, and goes to GROUND
> through a
> >> resistor.
> >> Normal voltage at that point can't be anything
> less than zero.
> >>
> >> Al
> >>
> >> Scott Roberts wrote:
> >>
> >>> Visit our web site - See http://www.njarc.org
> >>> _______________________________________________
> >>> Hi John- I'll reply to point:
> >>>
> >>>
> >>>
> >>>> I *strongly* recommend replacement of the main
> power
> >>>> supply filter caps... ...22/250
> >>>> should do nicely (which you have, I think)
> >>>>
> >>>>
> >>> Yes- I have them: still seem small to
> me...lol... I will put
> >>>
> >> them
> >>
> >>> in straight away.
> >>>
> >>>
> >>>
> >>>> Regarding your voltage measurements always keep
> in
> >>>> mind two things:
> >>>>
> >>>>
> >>>
> >>>
> >>>> The original Hallicrafters measurements were
> probably
> >>>> taken with a 1,000 ohms per volt VOM, which
> loads the
> >>>> circuit a little.
> >>>>
> >>>>
> >>> Yes- manual called for 1000ohm per volt VTVM.
> >>>
> >>>
> >>>
> >>>> Your DVM does not load the ckt at
> >>>> all. (Except for grid voltages, where Halli.
> may have
> >>>> used -- at least *should* have used -- a VTVM.)
> >>>>
> >>>>
> >>> Should I recheck with a VTVM?
> >>>
> >>>
> >>>
> >>>> Line voltage then was probably 110V.
> >>>>
> >>>>
> >>> Manual calls for 115VAC
> >>>
> >>>
> >>>
> >>>> Today's higher
> >>>> line voltages jack all the measurements up, at
> least a
> >>>> little bit. I'm *very* surpsied that your line
> voltage
> >>>> is only 113V.
> >>>>
> >>>>
> >>> 113 was through Variac. 119 is line voltage-
> numbers go up a
> >>> little when direct feed.(i.e: 6K7(IF Amp 1) goes
> up to 297
> >>>
> >> from
> >>
> >>> 269.5 on 119VAC)
> >>>
> >>>
> >>>
> >>>> OK, so much for that -- you took all of these
> >>>> measurements, but what is the radio DOING? Is
> it
> >>>> receiving *anything*? What are the symptoms? It
> does
> >>>> appear that something is wrong with the BFO,
> but
> >>>> that's no big deal.
> >>>>
> >>>>
> >>> Radio was, as dictated in manual- antenna &
> ground
> >>>
> >> disconnected,
> >>
> >>> RF & AF gain at Max(when I switched RF into max,
> got a
> >>>
> >> snapping
> >>
> >>> noise, like motorboating, but only briefly), no
> speaker
> >>>
> >> hooked
> >>
> >>> up. BFO numbers were all wacky- cannot access
> bottom of
> >>>
> >> socket,
> >>
> >>> used testing adapter between tube and socket.
> Tested in both
> >>>
> >> "On"
> >>
> >>> and "Off" positions.
> >>>
> >>>
> >>>
> >>>> Some of those measurements should be *negative*
> >>>> (control grids). Just a few volts in most
> cases. Check
> >>>> those again.
> >>>>
> >>>>
> >>> Yes- 6R7G #8 pin should read -7, reads +5.86
> >>>
> >>>
> >>>
> >>>> Lastly, the 10.450V in place of 10/25V IS
> overkill.
> >>>> Get that outta there. We have a few 10/50V caps
> left.
> >>>> They're tiny, and I think they're only 10 cents
> each!
> >>>>
> >>>>
> >>> Yep- I have it: just seemed SO DA** SMALL! (I
> still have
> >>>
> >> trouble
> >>
> >>> accepting the small sizes of newer
> electrolytics...lol)
> >>>
> >>>
> >>>> Regards,
> >>>>
> >>>> JR
> >>>>
> >>>>
> >>> Right now, I am tracing the electrical paths, to
> see if there
> >>>
> >> may
> >>
> >>> be some resistor issues. I will replace the
> overkill and the
> >>>
> >> two
> >>
> >>> original 16mf electrolytic caps, and retest.
> Should I hook up
> >>>
> >> the
> >>
> >>> speaker? And should I use a VTVM of my DMM
> instead?
> >>>
> >>> Thanks!
> >>> Scott
>
=== message truncated ===
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