Subject: GLOWBUGS digest 74

From: [email-masked]
Date: Fri, 12 Jan 1996 06:52:46 -0600 (CST)

GLOWBUGS Digest 74

Topics covered in this issue include:

  1) Voltage dropping for filament
	by Bruce Robertson <[email-masked]>
  2) crystal detector substitute
	by Bruce Robertson <[email-masked]>
  3) Re: Voltage dropping for filament
	by [email-masked] (michael silva)
  4) Re: Voltage dropping for filament
	by [email-masked] (William Hawkins)
  5) Newest Lindsay catalog goodies
	by [email-masked] (michael silva)
  6) crystal detector substitute
	by Duncan Cadd <[email-masked]>

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Date: Thu, 11 Jan 1996 23:58:42 -0500 (EST)
From: Bruce Robertson <[email-masked]>
To: glowbugs <[email-masked]>
Subject: Voltage dropping for filament
Message-ID: <[email-masked]>

A while back I got the crazy idea of building a 5w xmitter based on the 
design of Fred Sutter in a 30's QST article. In it he uses a voltage 
doubler rectifier tube and a beam pentode, both of which use 25v 
filaments. So I ordered up the tubes, and they arrived recently for me 
and my radio-building friend Brien, VE3VAW.

Now the thing is, we need to drop the excess 60v at .3A on these
filaments. A resistor will do the trick, of course, but it will put out
about 20w: that's hot and pretty useless. The article uses 'line cord':
what the heck is that, resistive wire or something? and is it totally out
of code now? How about a light bulb?  Anyone suggest a 24v or 48v bulb
that is right on the money? There's always a xformer but I think we're
both trying for the 1930s portable look (i.e. AC/DC). 

For that matter, how closely does one have to follow the voltages on 
filaments anyway? I imagine the tube burns out faster if you push it, but 
how much faster?

Again trying to borrow a life's experience with these devices,

73, VE3UWL

Bruce G. Robertson  Dept. of Classics, U. of T.     

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

Date: Fri, 12 Jan 1996 00:03:37 -0500 (EST)
From: Bruce Robertson <[email-masked]>
To: glowbugs <[email-masked]>
Subject: crystal detector substitute
Message-ID: <[email-masked]>

In my package from AES I got the crystal for a crystal radio which I'd 
like to build my dad as a retirement gift. The thing is, they were all 
out of the detector assemblies. I've never worked with one of these do it 
yourself diodes; does anyone have a good idea as to what I should rig up 
as a substitute cat's wisker? Should the tickler be copper or steel, 
stiff or soft? Also the crystal seems to be potted in some conductive 
cement; any idea how I should wire this into the circuit?

73, VE3UWL

Bruce G. Robertson  Dept. of Classics, U. of T.     

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

Date: Thu, 11 Jan 1996 22:07:26 -0800
From: [email-masked] (michael silva)
To: [email-masked]
Subject: Re: Voltage dropping for filament
Message-ID: <[email-masked]>

Bruce G. Robertson wrote:

>Now the thing is, we need to drop the excess 60v at .3A on these
>filaments...
> The article uses 'line cord': what the heck is that, resistive wire 
>or something? and is it totally out of code now?

Yep, the line cord had a third, resistance lead for dropping the excess 
filament voltage.  Doubt very much you can buy them new (except maybe 
from Antique Electronic Supply?).  They became obsolete when tube 
lineups that dropped the entire 110v across the heater string came into 
being (late 1930s?).  You could use a ballast tube to drop the voltage 
(assuming you can find one with the right rating).  It's just a 
resistor that plugs into a tube socket -- their advantage was mainly to 
get the heat on top of the chassis rather than underneath it.

I don't know about any 'gotchas' with this, but how about dropping most 
of the voltage by running the filament line in series with a (hidden) 
silicon diode.  That should give you 60 volts equiv., and you can drop 
the last ten with a much smaller resistor (or you could add a 12v .3A 
oscillator tube and have a MOPA rig).

73,
Mike, KK6GM

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

Date: Fri, 12 Jan 96 00:35:37 CST
From: [email-masked] (William Hawkins)
To: [email-masked], [email-masked]
Subject: Re: Voltage dropping for filament
Message-ID: <[email-masked]>

Went to an antique radio club meeting last year that had resistance
line cords as one of its subjects.  They were called "curtain
burners".  They no longer meet any codes, so they aren't made.
The usual way to replace them is with a diode (since there's no
DC mains left anywhere, right?) and enough resistance to make up
the difference.

Bruce asked about running the tubes on high voltage anyway, with
reduced life.  The problem is that life is an exponential function
of voltage.  Wish I could find the numbers, but you don't have to
drop volts very far (15-20% ?) to get 10 times the life.  When you
go towards the melting point, things probably go even faster.

Bill Hawkins  [email-masked]  612 895-2085  Minneapolis, MN  USA

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

Date: Fri, 12 Jan 1996 00:25:09 -0800
From: [email-masked] (michael silva)
To: [email-masked]
Subject: Newest Lindsay catalog goodies
Message-ID: <[email-masked]>

Hi all,

Just got my second Lindsay catalog, and it looks like old radio books 
are a booming market.  This one has a new book on regens, a book with 
reprinted chapters of the 1929 and 1934 ARRL Handbook, a 1922 parts 
catalog from Sears, etc, etc.  I've gotten a few of their books, my 
favorite so far being the "Official 1934 Shortwave Radio Manual".  
There are also lots of non-radio books offered, such as one on 
distilling moonshine, and lots of Tesla stuff.  Time to send off 
another order...

Nope, I didn't forget (well, almost):

Lindsay Publications, 815-935-5353.

73,
Mike, KK6GM

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

Date: Fri, 12 Jan 1996 10:41:29 +0100 (MET)
From: Duncan Cadd <[email-masked]>
To: [email-masked]
Cc: [email-masked]
Subject: crystal detector substitute
Message-ID: <[email-masked]>

Greetings, Bruce, from an overcast but dry Diepenbeek in N.E. Belgium!

> does anyone have a good idea as to what I should rig up 
> as a substitute cat's wisker? Should the tickler be copper or steel, 
> stiff or soft? 

All manner of things were used for this depending on what one had to hand, 
ergo, use what you have to hand!  For preference, it should be springy so a
small amount of pressure can be applied.  Phosphor bronze is excellent for
this.  A phosphor bronze cleaning brush for small calibre firearms will yield
a lifetime's supply of suitable wires!  But almost anything will do.

> Also the crystal seems to be potted in some conductive 
> cement; any idea how I should wire this into the circuit?

I'd advise against trying to solder it.  High temperatures will destroy the
rectifying action of the crystal, so solder the appropriate wire to a piece
of e.g. flat copper strip and bind that to the holder with for example a hose
clamp.

73,

Duncan  ON9CHU  /  G0UTY   G-QRP 8117

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End of GLOWBUGS Digest 74
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