[Amps] Gettering 4CX800A GU74b

Manuel R. Alonso kc4mne at bellsouth.net
Thu Oct 21 08:23:39 EDT 2004


----- Original Message ----- 
From: "Manuel R. Alonso" <kc4mne at bellsouth.net>
To: "Steve Thompson" <g8gsq at ic24.net>
Sent: Thursday, October 21, 2004 7:50 AM
Subject: Re: [Amps] Gettering 4CX800A GU74b


> From the website of ND2X
> http://www.nd2x.net/tube-prep.html
>
>
> THE PROBLEM:
> After I had obtained a few surplus Russian tubes from Dr Alex, UR4LL he
sent
> me an e-mail entitled "Starting Procedure". The subject of this message
> certainly piqued my curiosity! As I read it, I realized I had forgotten a
> very important aspect of using tubes which have spent a significant amount
> of time, often years, "on the shelf" awaiting use! Due to the nature of
> physical materials, a certain amount of gases are always trapped inside
the
> metals and ceramics, etc., used to construct each tube. A vacuum tube
> depends on a relatively hard vacuum to function without arcs and other
> undesired, often disasterously destructive, internal current flow. While
in
> storage, a certain amount of the gases trapped in its materials is
"leached"
> out into the vacuum of the tube. If one were to plug such a tube into an
> amplifier and apply all voltages and drive, the small amount of gas within
> the tube would ionize and provide said undesired internal conductive
paths;
> such conduction often reduces an otherwise useful tube to trash. It is,
> however, possible to prevent these events from occurring by taking some
> rather simple measures to prepare such tubes for use!
>
> THE SOLUTION:
> Fortunately, tube manufacturers considered this situation, and inside each
> vacuum tube is a metal surface called a "getter" - a surface made from
some
> particularly reactive metal like barium. Being very reactive, it will
react
> with more or less any molecule that hits its surface, and form a
> non-volatile reaction product. In a small glass tube, the getter is the
> shiny surface on the inside of the glass wall. The trick is to get the
atoms
> of gas to move around enough to strike the getter and become absorbed.
This
> is what UR4LL's e-mail addressed. I also did some reading on the internet
> and found an applicable Technical Bulletin from Svetlana and a very nice
> treatise by SM5BSZ, including input from SM6EHY, which put it all in
> perspective. I include three excerpts from SM5BSZ:
>
>
>   "As amateurs, we often use old tubes. They may be unused, but may have
> spent a very long time stored away. A high power tube should work at very
> high voltages without arcing so it has to have a very good vacuum. When
the
> tube is stored, vacuum gradually deteriorates over time and the procedures
> below will help to restore a good vacuum.
>
>   The cathode is the "heart" of the tube. There are several types of
> cathodes, and they have different properties. Read in the manufacturers
data
> book how to treat the cathode of the tube you are going to use. A pure
> tungsten cathode will give maximum tube life if the heater voltage is made
> as low as possible for the desired output power, while a thoriated
tungsten
> cathode may be damaged if it is underheated.
>
>   When the heater is switched on for the first time, it may be important
to
> allow it to reach its final temperature slowly. I have been told that a
slow
> heating, raising the voltage from zero to nominal gradually, over a time
of
> several hours, will increase tube life considerably in normal professional
> operation. I guess this has something to do with a rechrystalisation that
> takes place when the heater wire is heated for the first time, but I do
not
> really know."
>
>
> --------------------------------------------------------------------------
--
> ----
> PREPARING SURPLUS TUBES FOR USE
>
>
> From UR4LL:
>   1. Only Ufil during 12 hours min.
>   2. To ground all grids.
>   3. 25% of Ua during 4 hours.
>   4. 50% of Ua during 4 hours.
>   5. 100% of Ua during 4 hours.
> COMMENTS: We have found that some of the larger tubes do a lot better if
we
> bring filament voltage up, either over a period of a minute or so using a
> variac, or using the procedure in "Step 1", below, and leave the power on
in
> this manner (with cooling fan on or liquid coolant flowing) for three to
> five days. We have found, for example, that GS-23B operation can be
> SIGNIFICANTLY enhanced, especially for those which work at 23cM, by a
> minimum of five (5) days with the filament on as described!
>
> Subject to adjustments as outlined above, the steps shown below (prepared
16
> June 2000) will change as further experience dictates:
>
> Step 1:  Per SM5BSZ, I'm going to bring the filament voltage (Ufil) up
> slowly; probably 20% Ufil for the 1st hour, 40% during the 2nd hour, 60%
in
> the 3rd hour, 80% for the 4th hour and, finally, apply 100% Ufil after
four
> hours, leaving it applied until 12 hours has elapsed. I will turn the
forced
> air cooling on at the start of the second hour.
>
> Steps 2 & 3:  I have a variac on the input to my HV supply and will vary
the
> plate voltage (Ua, or anode voltage) as required to obtain the specified
> percentage for the specified period. If you don't have a means to vary
your
> HV, SM6EHY says, "Connect the anode through a 50 to 100 kiloohm resistor.
> Leave the tube with the plate voltage through this resistor for 2 hours.
If
> the tube has been unused several years, leave it for 24 hours." Most of my
> tubes are from surplus "spares stock" and are several years old. Based on
> this, I will have to err on the side of too much time at each level,
rather
> than trying to shorten the process in any way! UR4LL says to ground all
> grids before applying Ua; SM6EHY says nothing about the grids until his
> equivalent of step 4.
>
> Step 4:  Again, I will vary my HV using the power supply variac. SM6EHY
> suggests, "Now the vacuum is improved, and you can replace the 50 to 100 k
> ohm resistor by 1 k ohm and apply the screen grid voltage. Start with a
> reduced screen grid voltage for half an hour and then apply full voltage
and
> wait for half an hour again. In both cases, the control grid voltage
should
> be adjusted for negligible plate current." If I see plate current starting
> to creep up, I will unground the control grid and apply bias per SM6EHY.
>
> Step 5:  I will follow UR4LL's procedure. After step five, he says, "Tube
is
> ready for use." Step five per SM5EHY: "Now it is time to remove the plate
> resistor and start to use the tube with some RF." Click here To read
> SM5EHY's comments within the context of the SM5BSZ web page.
>
>
> Would be nice to Know how QRO does it!
>
> Is QRO using "NEW STOCK" Svetlana tubes with the 4CX800 marking, or
Surplus
> Russian Military "NEW OLD STOCK" tubes with the GU74b markings?
>
>
>
> Manny, KC4MNE
>
>
>
>
>
> ----- Original Message ----- 
> From: "Steve Thompson" <g8gsq at ic24.net>
> To: <amps at contesting.com>
> Sent: Thursday, October 21, 2004 7:31 AM
> Subject: Re: [Amps] Gettering 4CX800A GU74b
>
>
> >
> > > > Ray --  How does one getter a 4cx800A?
> > >
> > > I'm like Rich, how does one "Getter" a 4CX800?
> > http://antennspecialisten.se/~sm5bsz/recondit.htm for example
> >
> > Steve
> > _______________________________________________
> > Amps mailing list
> > Amps at contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>



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