[NJARC] Radio Debugging PS
Scott Roberts
ng19delta at yahoo.com
Fri Mar 7 14:54:52 EST 2008
John(and Al)
I made the changes, and it -did- pull the numbers a bit closer to
"factory ideal", although my 5 pins are still high- actually got
higher with the changes... And the beat osc. 6J7, is showing 8.75
on 3&4(should be 150, each) and 165 on pin 6(should be 350).
Also, I have a -32 on pin 5 of either 67 Mixer or 6J5G Osc.(I
have to recheck- it is showing on one in the first check, the
other on the second, so I may have written in the wrong box...)
I am going to retest the tubes before I proceed further.
Still trying to figure why the Beat Osc numbers are so low. They
are the same with BFO on or off, and with RF at high.
Oh- and I think that "motorboating like noise" came from the
meter! I noticed it coming form that area when I switched the RF
gain to full. I think it may have been out of adjustment: the
needle went full left. So I turned the adjuster just a little to
bring it back up to zero
As to VTVMs, I have several- now I have to remember which one
WORKS!
Scott
--- John Ruccolo <jr6v6gt at yahoo.com> wrote:
> Visit our web site - See http://www.njarc.org
> _______________________________________________
> 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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