I seem to recall the manual on a 1940's vintage 50 kw transmitter used
DC on the filament.
There was a recommendation to reverse the DC every so often to equalize
the work on the
filament wire ... I am old, it's really from the way- back machine, but
I do remember recommendations
about reversing filament voltage on DC filaments every now and again...
Just more to think about, not sure if it means anything at this point
73
ed K0KL
On 4/26/2014 11:00 AM, amps-request@contesting.com wrote:
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Today's Topics:
1. low pass filter fail ;) (Benedikt Sveinsson)
2. Re: WEIRD ONE SOLVED (Bryan Swadener via Amps)
3. Filament Voltage Question (John Lyles)
4. FW: Filament Voltage Question (Matt)
----------------------------------------------------------------------
Message: 1
Date: Fri, 25 Apr 2014 21:49:47 +0000
From: Benedikt Sveinsson <benedikt@ok.is>
To: Amps <amps@contesting.com>
Subject: [Amps] low pass filter fail ;)
Message-ID: <B579991C234CB04F9D4C9EAE8AC57A49492CC1@OK-MAIL.ok.is>
Content-Type: text/plain; charset="us-ascii"
I have been building a 2M SSPA - final part in the puzzle has been the low pass
filter.
After building this filter, copied the design from W6PQL - but I have limited
resources here in TF land, so I don't have access to good PCB materials. But
the filter was measured using a mini VNA Pro analyser with good results. 1:1.2
SWR on the operating frequency and cuttoff starts around 150Mhz
well, after transmitting about 10s I noticed a drop in output power, I took the
cover off and aimed the camera while transmitting
This is what happened on youtube: https://www.youtube.com/watch?v=9lU3I3BgmkE
I suspect there is something else wrong, as this happened very fast 10-15s -
and solder melts!
Guess I will go and find teflon sheets and make my own capacitors with copper ;)
73, Benni TF3CY
------------------------------
Message: 2
Date: Fri, 25 Apr 2014 17:19:47 -0700 (PDT)
From: Bryan Swadener via Amps <amps@contesting.com>
To: "amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] WEIRD ONE SOLVED
Message-ID:
<1398471587.59031.YahooMailNeo@web122104.mail.ne1.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1
And no more 60Hz hum from feeding the bias thru the
filament xfmr CT.
vy 73,
Bryan WA7PRC
----------------------------------------------------------------------
Date: Thu, 24 Apr 2014 19:50:07 -0400
From: Bill VE3NH
Subject: [Amps] WEIRD ONE SOLVED
The negative lead of the bias board should have been grounded
instead of attaching to B- since the GI7-B has an indirectly heated
cathode whose pin is common to one side of the filament.
Bottom line: everything now works as it should.
Now, bring on the 6M DX!? Thanks again, Paul.
Bill VE3NH
------------------------------
Message: 3
Date: Fri, 25 Apr 2014 23:39:25 -0600
From: John Lyles <jtml@losalamos.com>
To: amps@contesting.com
Subject: [Amps] Filament Voltage Question
Message-ID: <535B468D.9030706@losalamos.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
When direct heated filaments of thoriated tungsten (usually 1-2% thoria)
have a lot of hours of operation (thousands), they become brittle and
easy to break. Older tubes are much more prone to shipping damage from
broken filaments for this reason. Grain growth occurs in the
microstructure of the metal. Thin higher voltage filaments would be even
more fragile in this condition. Large filament wires or bars can be
modified in thickness along the length to try and create a more uniform
temperature and electron emission. Near the bottom, the leads help
conduct heat away and reduce the temperature. By necking down the wire,
the temperature at this point can be raised. Lots of tricks like this
are possible with fat high current filament structures.
The filaments in the RCA 7835 are 96 vertical bars, each carrying ~70
amperes DC. End result is a 5 VDC filament with 6800 amperes of current.
The RCA 4616 has a similar complex of vertical bars, much smaller, and
has a terminal voltage of 0.95 VAC!
73
John
K5PRO
-------------
There is another issue too: With a directly heated cathode (filament),
there is an unintentional bias across the filament. Whether using AC or
DC, one end of the filament will be more negative than the other and
that adds a grid-cathode bias to the equation. With DC the bias is
constant, with AC it alternates of course. More anode current will be
emitted from the negative end and less from the positive end.
I don't know if this causes any actual harm, but I can't imagine it
helping any.
73, Bill W6WRT
------------------------------
Message: 7
Date: Tue, 22 Apr 2014 13:13:26 -0600
From: "Jim Garland" <4cx250b@miamioh.edu>
To: "'Fuqua, Bill L'" <wlfuqu00@uky.edu>, <amps@contesting.com>
Subject: Re: [Amps] Filament Voltage Question
Message-ID: <00ad01cf5e5e$f1790250$d46b06f0$@miamioh.edu>
Content-Type: text/plain; charset="us-ascii"
Good point, Bill. I hadn't thought of that, but that's obviously a
consideration for VHF/UHF tubes with directly heated cathodes.
Jim
>
> --------------------------------------------
> On Tue, 4/22/14, Jim Garland <4cx250b@miamioh.edu> wrote:
>
> Subject: [Amps] Filament Voltage Question
> To: amps@contesting.com
> Date: Tuesday, April 22, 2014, 8:19 AM
>
> I was reading the data sheet this
> morning on the 4CX3500A and noticed the
> filament requirements are 5V@90Amps. It occurred to me
> that I've never
> understood why so many tubes with indirectly heated cathodes
> have such
> low-voltage - high current filaments. Since the only thing
> the filament is
> used for is to heat the cathode, then why not design it to
> run at, e.g.,
> 115V@4A? That sure would be a lot easier to implement. I'm
> sure there's a
> reason, howevrr, and would appreciate somebody informing of
> it!
>
> 73,
>
> Jim W8ZR
------------------------------
Message: 4
Date: Sat, 26 Apr 2014 02:15:23 -0500
From: "Matt" <maflukey@gmail.com>
To: <amps@contesting.com>
Subject: [Amps] FW: Filament Voltage Question
Message-ID: <14f101cf611f$4aff75d0$e0fe6170$@gmail.com>
Content-Type: text/plain; charset="us-ascii"
I am perhaps confused. In my experience, grain growth generally produces
increased ductility and improved (or restored depending on your point of
view) yield strength more-or-less according to the Hall-Patch relationship
(yield strength is proportional to the square root of grain size). It would
seem that grain refinement, not growth, would contribute to increased
brittleness.
Matt
KM5VI
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of John Lyles
Sent: Saturday, April 26, 2014 12:39 AM
To: amps@contesting.com
Subject: [Amps] Filament Voltage Question
When direct heated filaments of thoriated tungsten (usually 1-2% thoria)
have a lot of hours of operation (thousands), they become brittle and easy
to break. Older tubes are much more prone to shipping damage from broken
filaments for this reason. Grain growth occurs in the microstructure of the
metal. Thin higher voltage filaments would be even more fragile in this
condition. Large filament wires or bars can be modified in thickness along
the length to try and create a more uniform temperature and electron
emission. Near the bottom, the leads help conduct heat away and reduce the
temperature. By necking down the wire, the temperature at this point can be
raised. Lots of tricks like this are possible with fat high current filament
structures.
The filaments in the RCA 7835 are 96 vertical bars, each carrying ~70
amperes DC. End result is a 5 VDC filament with 6800 amperes of current.
The RCA 4616 has a similar complex of vertical bars, much smaller, and has a
terminal voltage of 0.95 VAC!
73
John
K5PRO
-------------
There is another issue too: With a directly heated cathode (filament), there
is an unintentional bias across the filament. Whether using AC or DC, one
end of the filament will be more negative than the other and that adds a
grid-cathode bias to the equation. With DC the bias is constant, with AC it
alternates of course. More anode current will be emitted from the negative
end and less from the positive end.
I don't know if this causes any actual harm, but I can't imagine it helping
any.
73, Bill W6WRT
------------------------------
Message: 7
Date: Tue, 22 Apr 2014 13:13:26 -0600
From: "Jim Garland" <4cx250b@miamioh.edu>
To: "'Fuqua, Bill L'" <wlfuqu00@uky.edu>, <amps@contesting.com>
Subject: Re: [Amps] Filament Voltage Question
Message-ID: <00ad01cf5e5e$f1790250$d46b06f0$@miamioh.edu>
Content-Type: text/plain; charset="us-ascii"
Good point, Bill. I hadn't thought of that, but that's obviously a
consideration for VHF/UHF tubes with directly heated cathodes.
Jim
>
> --------------------------------------------
> On Tue, 4/22/14, Jim Garland <4cx250b@miamioh.edu> wrote:
>
> Subject: [Amps] Filament Voltage Question > To: amps@contesting.com >
Date: Tuesday, April 22, 2014, 8:19 AM > > I was reading the data sheet
this > morning on the 4CX3500A and noticed the > filament requirements
are 5V@90Amps. It occurred to me > that I've never > understood why so
many tubes with indirectly heated cathodes > have such > low-voltage -
high current filaments. Since the only thing > the filament is > used
for is to heat the cathode, then why not design it to > run at, e.g., >
115V@4A? That sure would be a lot easier to implement. I'm > sure there's
a > reason, howevrr, and would appreciate somebody informing of > it!
>
> 73,
>
> Jim W8ZR
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