Subject: GLOWBUGS digest 177

From: [email-masked]
Date: Fri, 3 May 1996 22:26:00 -0500 (CDT)

GLOWBUGS Digest 177

Topics covered in this issue include:

  1) Fuse rebuilding
	by [email-masked]
  2) Lamb bulb resistances for experimental use
	by [email-masked]
  3) World's Simplest Field Strength Meter
	by [email-masked]
  4) Re: Fuse rebuilding
	by [email-masked]
  5) Regenerative receiver love rekindled
	by [email-masked] (Michael Herr)
  6) Re: Fuse rebuilding/funzies
	by [email-masked]
  7) The 69er
	by Jeff Duntemann <[email-masked]>
  8) Re: The 69er
	by "Deane D McIntyre"  <[email-masked]>
  9) Could there be a 1-tube superhet?
	by Jeff Duntemann <[email-masked]>

----------------------------------------------------------------------

Date: Fri, 3 May 1996 12:55:57 -0400 (EDT)
From: [email-masked]
To: [email-masked], [email-masked]
Cc: [email-masked] ()
Subject: Fuse rebuilding
Message-ID: <[email-masked]>

Whilst attempting to resurrect a fine old ancient mariner, I ran out of
HV fuses (the originals had rotted away in storage before I got the beast).
My last spare is used up and I get deep willies trying to just bypass them.

Thinking that somewhere in the deep dark reaches of the past I had seen
a table of fusing currents for plain copper wire, I looked and looked and
searched high and low and was unable to find that table.  By sheer chance,
last night, while going through a bunch of papers, I found the long lost
treasure.  Now I am able to reconstruct my HV fuses.  So that others
may not have to scratch their heads like I did, and hopefully so others
may contribute to the table and make it available on the archives I
will type in what I have.

                ----------------------------------------
                Fusing Effects of Current on Copper Wire
                ----------------------------------------

        (Note --- the original source for this is long lost, but it
        may have been in an old 50's or earlier Handbook of Chemistry
        and Physics.)

        B&S Guage   Fusing Current in Copper Wire
        ---------   -----------------------------

        10          333
        12          235
        14          166
        16          117
        18           83
        20           58
        22           41
        24           29
        26           21
        28           15
        30           10
        32            7.3
        34            5.1
        36            3.6
        37            3.1
        38            2.5
        39            2.2
        40            1.8

Maybe someone else has other values for other metals that might be
usable.  Perhaps aluminum wire might also be good in a pinch, if
anyone has tables of fusiblity for aluminum.  For most purposes, it
is probably best to stick with copper.

We checked for makers of HV fuses, and no-one makes them anymore that
we can find.  Also, cartridge fuses in the large cartridges are no longer
being made.  But, such fuses can be rebuilt if you can find the fuse links
or the right size of fusible wire.  Currently I am using individual strands
of stranded copper wire (No. 40 or smaller) on some of my HV fuses, and
it seems to work OK.  Handling that size wire is sometimes a problem to
prevent breakage, but one has to make do these days with what one can
find, just like in the early days.

Good Luck

73/ZUT DE NA4G/Bob UP

------------------------------

Date: Fri, 3 May 1996 13:28:28 -0400 (EDT)
From: [email-masked]
To: [email-masked], [email-masked]
Cc: [email-masked] ()
Subject: Lamb bulb resistances for experimental use
Message-ID: <[email-masked]>

Another treasure surfaces from the deep dark recesses and bilges.

               ----------------------------------------
               TABLE OF TUNGSTEN LAMP RESISTANCE VALUES
               ----------------------------------------

        (Note: the original source for this is long lost, but it
        has ``Popular Science Monthly Shop Data'' written on the
        xerox that it came from.)

        Lamp Wattage     Approximate Resistance in Ohms
                         Cold     25%     50%     75%     100%
        ------------     ---------------------------------------

        6                193      1390    1837    2127    2400
        10               113       822    1094    1293    1440
        15                73       540     722     856     960
        25                42       318     427     509     576
        40                25       173     253     299     360
        50                21       141     206     241     288
        60                17       117     171     201     240
        75                12        98     136     154     192
        100               10        77     104     116     144
        150                7        48      69      84      96
        200                5        36      51      62      75

        Note:  Percentages are in percentages of 120vac applied
        across the bulb while it is used as a series resistor.

Looking at the table, one can easily see why a 200 watt lamp makes such a
good dummy load for the average coax fed rig --- it is within the 30-100
ohm range at all output powers.  Also, at MF and HF, the inductance and
series effects of using a coil in a filament as a resistor are essentially
nil.  For open wire feeders, choose a power and resistance rating for
your rig and open wire impedance 300-600 ohms.

Using such a table, one can easily use lamp resistances as series current
limiters for battery charging, etc.  In my chargers, they drop about 24
volts to a 6 or 12 volt battery, so I use the 25% column, and it works
quite well.  Also, series lamps make great bleeder loads when run at
about 25 percent power or so, and it will stabilize your power supplies
on OT rigs, quite well.  4 watt christmas tree lamps or 7.5 watt night
lamps work quite well in this vein, for light loading and 10 or 15 watters
work well for heavier loading.  Use one bulb for every 60 volts of HV
to bleed (Yeah, I know that is a lot of lamps, but they sure glow nicely
and keep the shack warm in winter!).

The basics of the use of lamp bulb resistances are well covered in two
QST articles, suitable for all amateur, and especially all boatanchorite
and glowbuggite uses.

1.  Redgrave, D.C., KA1NA.  The light-bulb resistor.  QST, March, 1934,
    pages 36-37.

2.  Hamburger, F., Jr., W3AMM.  The incandescent lamp as a resistor.
    QST, July, 1934, page 31.

Good Luck

73/ZUT DE NA4G/Bob UP

------------------------------

Date: Fri, 3 May 1996 13:44:10 -0400 (EDT)
From: [email-masked]
To: [email-masked], [email-masked]
Cc: [email-masked] ()
Subject: World's Simplest Field Strength Meter
Message-ID: <[email-masked]>

Another treasure surfaced from the bilges.....

                    -------------------------------------
                    WORLD'S SIMPLEST FIELD STRENGTH METER
                    -------------------------------------

        (Note: the source for this was an obscure article in 73
        magazine, some years back, but I can't find the original
        citation for it.)

             Have you ever needed to tune up your OT rig and not
        been able to use a normal ``SWR meter''?  After all, OT
        rigs never knew what SWR was anyway.  It is essentially
        a null item on OT rigs fed with tuned lines or no lines.
        My OM, a sparks since the earliest days, always tuned with
        a field strength meter, even when running commercial gear.
        It worked for 70 years for him, and has for 25 years for me.

        The following circuit is ascribed to Jo Jennings/W6EI (SK).
        It was written up for 73 in a short half page article by
        Lloyd M. Jones/W6DOB.  I have been teaching all my classes
        in Ham Radio, using this device for instructional purposes,
        since it really, really works!  Even newcomers can get a
        grip on it and make it work, the first time.  One does not
        even need a case for the meter.

                                  |
                                  |
                                  |
                                  |
                                  |  any sort of little
                                  |  antenna 10-36 inches
                                  |  long or thereabouts
                                  |
                                  |
                                  |
                                  |
                         DIODE    |   DIODE
                      +----|>|----+----|>|----+
                      |                       |
                      |                       |
                      |                       |
                      |        -     +        |
                      +-------- METER --------+

        73/ZUT DE NA4G/Bob UP

------------------------------

Date: Fri, 3 May 1996 13:59:20 -0400 (EDT)
From: [email-masked]
To: [email-masked] (William Hawkins)
Cc: [email-masked] (), [email-masked],
Subject: Re: Fuse rebuilding
Message-ID: <[email-masked]>

> 
> Um, there's more to it than just melting the wire.  The arc has to be
> controlled - especially at high voltage.  Are you talking about the
> cartridges that have end caps that screw on to hold the wire _and_
> are filled with powder?

I am talking about the paper fuze cartridges that are used in things
like the BC-191 and BC-375, TCM, TDB, and many other ancient transmitters
for which replacements are non-existant.  These are the 2 or 4 inch long
tubes with brass end caps.  They are use in the B+ lines and in high
current filament lines, etc.  They are not used in primary lines.

I have to disagree slightly in that there is nothing more to it than
letting the fuse link blow (except for containing the fire as the wire
fuses).  All that the link has to do is open at a reasonable approximation
to the desired current.  Of course, if one is constructing one from
scratch, then it should be properly insulated and properly fireproofed
so you don't catch the rig or the house afire.  That is obvious.

> There's also 'clearing time' and overcurrent characteristics, that
> usually dictate some alloy - not copper.  That's not as important as
> having _something_ for a fuse, but copper can allow pretty high peak
> fault current.  I'd be sure that there were real fuses in the connection
> to the power company, on the primary side of the HV transformer.

We are talking about secondary fusings here, where non-existant fuse
cartridges or links exist anymore.  I would not suggest anyone do this
in the primary side --- use normal fuses for that, replacing holders
if necessary.  But, have you tried to find a 2000 volt 250ma fuse, lately?
These you may have to rebuild.

What I do is carefully remove the end caps from the paper or bakelite
tube and then install replacement copper wire fuse link.  It has always
worked fine for me.  If the fuse link is within, 200% of original value,
that will usually work just fine in normal kinds of BA applications where
no currently available replacements exist.  Usually, I choose one step
less in fusing current just to be on the safer side.  That is usually
40 or smaller wire sizes.

The only other alternative that I can think of, in a practical sense,
would be to wire up pigtails on 250v fuses and use those as replacement
insert fuse links, in these cartridges.  I am not sure these would work
any better.

If anyone has any other insights into this, kindly let me know, OK?
I have been plagued with this non-existent fuse link problem for some
20 years now, and the fusible copper links are the only thing that I
can find that suitably replaces originals, long since unavailable.

> Bill Hawkins

Thanks for the concerns, Bill.

73/ZUT DE NA4G/Bob

------------------------------

Date: Fri, 3 May 1996 10:31:27 -0700 (PDT)
From: [email-masked] (Michael Herr)
To: [email-masked]
Subject: Regenerative receiver love rekindled
Message-ID: <v01530500adb0e2e1ae97@[199.120.150.38]>

Hello gang,
     I dusted off the old HeathKit regen receiver model GR-81 the other
night and fell in love. It's a small box receiver with the 3 tube
configuration (detect, audio and rectifier). As a kid of 12 or so year I
had built it after picking prunes one summer to earn the money. Back then I
enjoyed listing to the broadcasters and amateurs alike. I packed it away
and forgot about it. Well, the other night I decided to listen to 160. Not
having a receiver for it I remembered the regen and pulled it out. Firing
it up I reacquainted my self with regen operation. Since that first night
I've had a blast! No digital readout, no AM / SSB selection. Signals don't
sit there and present themselves like a local FM station but rather they
have to be coaxed, tickled as it was to show their head and then after
working on it the station finally comes forward. A lot like catching a 10
pound catfish on a 2 pound line. A lot like QRP. One has to listen to the
signal and understand what is happening, not just look up the frequency and
punch it in! What a ball! I think it's now time to get back to the 3A4 rig
I was working on.
72
Mike WA6ARA

ps - anybody remember an article on a rig based upon the 6T9 tube? I
believe there was an AM version of it. I think it may have made one of the
ARRL handbooks.

------------------------------

Date: Fri, 3 May 1996 14:39:07 -0400 (EDT)
From: [email-masked]
To: [email-masked] (Paul H. Bock)
Cc: [email-masked] (), [email-masked],
Subject: Re: Fuse rebuilding/funzies
Message-ID: <[email-masked]>

> 
>      Boy, you guys would love how they handled fuses in Morocco 
> when I lived there.....I was staying in the hotel in Kenitra (nee 
> Port Lautey) and the circuit serving my room went dead.  I 
> happened upon the Duty Electrician in the hall changing the fuse 
> - well, actually, he removed the cover from a Large Porcelin Box 
> which looked like it had been built about 1910, and pulled out a 
> porcelin block with heavy brass prongs on either end, and 
> proceeded to carefully wind several turns of what looked like 
> ordinary solder around the two prongs to "connect" them, then 
> plugged the sucker back into the Large Porcelin Box and voila! - 
> my room again had electricity.
> 
>    73,
>    Paul, K4MSG

EEK!

Paul.... from the practical point, I wonder if anyone has done any
experimentation (at the ham level or in commercial or laboratory
settings, since it seems we need to have that kind of authority),
on using this ``solder'' alloy sort of fusible link.  Is there any
way to backtrack and find out what exactly was used as that link?

I have seen lots of spools of some sort of hairlike extremely fine
solder around here lately from a company that went belly up.  It looks
like about no. 35 or smaller solder wire.  The only problem I would
have with that approach is that the solder contains resin which will
burn, hence would not be suited to use as good a fusible link as would
a plain metal.

Anyone else seen these early type fusible link systems around?

Since my hind quarters ride on these kinds of fuses, I do have a
vested interest in making sure such things really do work.  I know
my copper links work, since I have inadvertently blown one or two
over the years.

Can anyone cite some literature on fuses, early or modern, preferrably
good sound technical material?  The earliest thing I can find relating
to radio is from Loomis (1925) who recommends plate circuit fusing on
tubes greater than 5 watts output power.  ``Appropriate fuses may be
purchased, or they may be made from tinfoil.  The tinfoil melts easily
if an overload of current passes over it.  The right size may be
determined by experimentation.  If a memorandum of the size of the strip
is preserved, it is thereafter only necessary to cut a new fuse as needed.
The tinfoil is easier to handle if pasted to bristleboard.  Contact is
made with small clips."  She also references earlier that ``The cartridge
fuse consists of a piece of wire, or a flat strip of an alloy of lead
and tin, imbedded in a misture of asbestos and chalk, and held in a fiber
cartridge shaped container, having copper or brass caps at each end which
fit into copper clips, thus making contact with the circuit.''
In this case she references the use of a wire as opposed to an alloy strip
as a fusible material.  Other classic writers, such as Ghirardi or
Bucher don't even mention fuses at all.

As No. 5 Alive used to say, .....``Need input!''

Bob/NA4G

------------------------------

Date: Fri, 3 May 1996 12:36:28 GMT
From: Jeff Duntemann <[email-masked]>
To: [email-masked]
Subject: The 69er
Message-ID: <[email-masked]>

Mike WA6ARA said:

ps - anybody remember an article on a rig based upon the 6T9 tube? I
believe there was an AM version of it. I think it may have made one of the
ARRL handbooks.

If you mean a small 5-watt CW transmitter, yes--not only do I know where the
circuit is, I built it, and have it on my shelf.  I pulled the power
transformer for another project some years ago, but if I find another
transformer that'll fit in that space (I built it small) it could live again.

I'm not aware of a version that puts out AM.  The original circuit was
published in QST about 1975 (I'll check tonight when I get home, where all
my circuit files are) and it was designed by Lew McCoy.

I called it the 69er, which was a pun on 6T9er.  It really had no catchy
name in the original article.

As a project it was tricky to build because there are *12* pins on a
Compactron tube, and getting all the damned components connected to the
socket was a very fussy business.  On the other hand, it made for a very
small, very tight rig for 5W out.

Compactron tubes are fairly abundant and cheap, because they appeared at the
End of Things, and there were gazillions of them in boxes on TV shop shelves
around the country when tube equipment kind of went away.  I built another
Compactron project in 1966 that's worth mentioning: A regenerative radio
from a Pop Electronics article called "One Tube--All Bands" or something
close to that.  I forget the number of the tube right now, but it was a
triple triode with one for the detector and two for audio.  It drove a
speaker to earsplitting volume, and shook the house on the downbeat when WWV
hit the hour.  (WWV's late and lamented CW ID was the first CW I ever heard,
a thunderous, authoritative announcement that I can still hear from any of
several radios in my history.)

The radio had a defect common to any simple "all-band" regen: By using a 365
pf main tuning cap, tuning was *very* touchy, as the tiniest angular force
on the shaft would send the passband skittering hundreds of cycles up or
down the band.  CW and especially SSB were murder to tune in.  AM BC and SW
was much better, and that's most of what I used it for.

I lost the magazine with the article long ago, but some years back I found
an old RCA hobbyist project book that basically reprinted the article.  It
was a fun project but I do NOT recommend it for amateur band use.

I've learned a lot about designing regen radio coils over the years, and
when I get a moment I'll write it up and summarize it here.  I wound one the
other night on a Safeway One-A-Day vitamins bottle, which miraculously *just
fits* an octal tube base into its neck.  Two self-tapping 6-32's and you're
there.

--73--

--Jeff Duntemann KG7JF
  Scottsdale, Arizona

------------------------------

Date: Fri, 3 May 1996 14:17:55 -0600
From: "Deane D McIntyre"  <[email-masked]>
To: [email-masked], [email-masked]
Subject: Re: The 69er
Message-ID: <[email-masked]>

In message <[email-masked]>  writes:
> 
> Mike WA6ARA said:
> 
> ps - anybody remember an article on a rig based upon the 6T9 tube? I
> believe there was an AM version of it. I think it may have made one of the
> ARRL handbooks.
> 
> 
> If you mean a small 5-watt CW transmitter, yes--not only do I know where the
> circuit is, I built it, and have it on my shelf.  I pulled the power
> transformer for another project some years ago, but if I find another
> transformer that'll fit in that space (I built it small) it could live again.
> 
> I'm not aware of a version that puts out AM.  The original circuit was
> published in QST about 1975 (I'll check tonight when I get home, where all
> my circuit files are) and it was designed by Lew McCoy.

The CW rig is in the early 70's ARRL Handbooks (1973 anyhow). The AM
rig also using the 6T9 (two if I remember correctly) is in the late
60's Handbooks (1969 anyhow). 6T9's are cheap from Antique Electronic
supply (something like $2.30). I ordered a few a couple of months ago
for use in one (or both) of these projects...have not got around to
it yet (story of my life). 

>Compactron tubes are fairly abundant and cheap, because they appeared at the
>End of Things, and there were gazillions of them in boxes on TV shop shelves
>around the country when tube equipment kind of went away.  I built another
>Compactron project in 1966 that's worth mentioning: A regenerative radio
>from a Pop Electronics article called "One Tube--All Bands" or something
>close to that.  I forget the number of the tube right now, but it was a
>triple triode with one for the detector and two for audio. 

Sounds like another fun project. The possible tubes would be 6MD8, 6MJ8,
6MN8, 6J9 or 6U10. Do any of these sound familiar, there are likely others?

73, Deane D McIntyre VE6BPO
[email-masked]

------------------------------

Date: Fri, 3 May 1996 14:41:26 -0700
From: Jeff Duntemann <[email-masked]>
To: [email-masked]
Subject: Could there be a 1-tube superhet?
Message-ID: <[email-masked]>

Deane said:

>Sounds like another fun project. The possible tubes would be 6MD8, 6MJ8,
>6MN8, 6J9 or 6U10. Do any of these sound familiar, there are likely others?

I'm pretty sure it was the 6U10.  I'll find the circuit and describe it here
by Monday.  It was fun, but it was NOT a ham receiver.  You'd have to
completely rethink the coil/tuning cap arrangement, but hey, Are We Not Men?
Might be worthwhile, tho I'm unlikely to do it myself.  I rarely build the
same circuit twice.

But here's a question: Is it possible to build a 1-tube superhet??  Some of
those late-era compactrons had a LOT of stuff in them.  Suppose we used a
signal diode for the detector.  Is there a Compactron (or any multipart
tube) with enough guts to be a superhet all by its lonesome?  That would be
one HELL of a cool project.

You could do without an RF amp and AGC.  You'd still need an oscillator
section, a mixer section (or one converter section) plus an IF amp and an
audio amp.  Without requiring speaker volume you would need only one audio
stage.  To me that sounds just barely possible.  Anybody got a complete
listing of Compactron tubes?  Is there a bottle with the balls to pull it off?

I've never yet built a tube superhet.  This one I would make time to build.

--73--

--JD--

------------------------------

End of GLOWBUGS Digest 177
**************************