[Amps] Amps Digest, Vol 136, Issue 42

Sat Apr 26 17:58:20 EDT 2014

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 at 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 at ok.is>
> To: Amps <amps at contesting.com>
> Subject: [Amps] low pass filter fail ;)
> Message-ID: <B579991C234CB04F9D4C9EAE8AC57A49492CC1 at 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 at contesting.com>
> To: "amps at contesting.com" <amps at contesting.com>
> Subject: Re: [Amps] WEIRD ONE SOLVED
> Message-ID:
> 	<1398471587.59031.YahooMailNeo at 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 at losalamos.com>
> To: amps at contesting.com
> Subject: [Amps] Filament Voltage Question
> Message-ID: <535B468D.9030706 at 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 at miamioh.edu>
> To: "'Fuqua, Bill L'" <wlfuqu00 at uky.edu>,	<amps at 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 at miamioh.edu> wrote:
>   >
>   >  Subject: [Amps] Filament Voltage Question
>   >  To: amps at 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 at 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 at 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 at gmail.com>
> To: <amps at 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 at contesting.com] On Behalf Of John Lyles
> Sent: Saturday, April 26, 2014 12:39 AM
> To: amps at 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 at miamioh.edu>
> To: "'Fuqua, Bill L'" <wlfuqu00 at uky.edu>,	<amps at 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 at miamioh.edu> wrote:
>   >
>   >  Subject: [Amps] Filament Voltage Question  >  To: amps at 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 at 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 at 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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>
> End of Amps Digest, Vol 136, Issue 42
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