[Amps] Gettering 3-500 Tubes
Carl
km1h at jeremy.mv.com
Mon Nov 7 09:11:17 PST 2011
It might let in air but that is not the type of gas we are discussing that
comes from the anode getter coating and must be recombined with it.
Its been awhle since Ive had an unsupported 3-400/500Z but they were no more
prone to air leakage then well built later ones. The SLC plant debacle in
the late 80's is something altogether different.
Carl
KM1H
----- Original Message -----
From: "Jim W7RY" <jimw7ry at gmail.com>
To: <amps at contesting.com>
Sent: Sunday, November 06, 2011 7:31 PM
Subject: Re: [Amps] Gettering 3-500 Tubes
One of the problems with the older 3-500s is if they are rocked when removed
from the sockets. This is hard on the filament seals and can let in gas.
73
Jim W7RY
--------------------------------------------------
From: "Carl" <km1h at jeremy.mv.com>
Sent: Saturday, November 05, 2011 6:16 PM
To: "rbethman" <rbethman at comcast.net>; <amps at contesting.com>
Cc: "R Johnson" <rjohnson at tmlp.com>
Subject: Re: [Amps] Gettering 3-500 Tubes
> Actually we all should be very concerned about keeping the 3-500Z
> gettered,
> it is one of the most prone tubes for needing it.
> There is also a big difference between air leakage past the seals and
> outgassing from the anode.
>
> Just "trying them as they are" is a great way to destroy the tubes as well
> as damage other components.
>
> Gettering the 3-500 and many other tubes requires the anode get hot enough
> to show at least a bright red for as little as 10 minutes to many
> hours.The
> getter is the coating on the anode in most modern glass transmitting tubes
> with sheet metal or graphite anodes.
>
> Unfortunately doing that at the amps operating voltage will often lead to
> a
> gas arc in the tube and most amps dont have sufficient protection
> circuitry
> to shut down fast.
>
> The procedure Ive recommended here and elsewhere is to run the HV at a
> level
> that wont sustain an arc, I use 900-1000V and then apply a bias voltage
> that
> allows sufficient plate current to flow to color the anode.
>
> For a 3-500 this is about 300-350W of dissipation so plenty of air flow is
> needed.
>
> A SB-220 can be temporarily modified to do this. The filament supply is
> fine
> but the bias supply wont be used, disconnect it. The HV needs to be variac
> controlled and an adjustable bias supply is needed which can be just
> about
> any small 0-30 or 40VDC supply since there will be no grid current being
> drawn (unless it arcs). The HV can be run a little higher if youre a bit
> low
> on the bias but I wouldnt go over 1200V for the initial run.
> Look at the constant current curves to get an idea of how the voltages
> interact.
> www.g8wrb.org/data/eimac/3-500Z.pdf
>
> Let the first pass run for 15 minutes, there should be no gas glow. Then
> try
> it at 1250V and then 1500V for 15 minutes each and adjust the bias each
> time
> for the same dissipation. When I see just the trace of gas glow I back
> down
> 250V and let it cook for an hour and then try a higher voltage again.. It
> takes time and patience with some tubes before they pass the test at
> 2500-3000V. Dont let the SB-220 HV transformer overheat, just do one tube
> at
> a time...the transformer is only 500VA CCS.
>
> Once the tubes are fully gettered and the amp is in normal use then its a
> good idea to get the tubes hot on a regular basis of once a month or so.
> Running as an AM linear is an easy and fun way to do it.
>
> Carl
> KM1H
>
> .
>
> ----- Original Message -----
> From: "rbethman" <rbethman at comcast.net>
> To: <amps at contesting.com>
> Cc: "R Johnson" <rjohnson at tmlp.com>
> Sent: Saturday, November 05, 2011 7:08 PM
> Subject: Re: [Amps] Gettering 3-500 Tubes
>
>
> I wouldn't be concerned with "Gettering".
>
> *IF* there is air leakage into the tubes, they will show a cloudy gassy
> look.
>
> Go ahead and try them as they are after you've gotten the rest sorted out.
>
> *IF* it was me, I'd replace the capacitors in the HV section. 20 years
> is a long time, and Heath didn't always use the "High" end parts.
>
> Bob - N0DGN
>
> On 11/4/2011 12:05 AM, R Johnson wrote:
>> I have just been given an old SB-220. It has been sitting in an attic for
>> 20+ years.
>>
>> I have removed the tubes and have been bringing the voltage up slowly
>> to reform the filter caps. When I get to 120V in and the caps aren't
>> steaming
>> and/or blowing smoke I'll be ready to check it with the tubes installed.
>>
>> I know that the need 3-500's will need to be "Gettered" to remove any gas
>> diffusion
>> thru the metal to glass seals on the tube.
>>
>> I read a procedure on (probably) on this list on how to do it.
>> Now that I need it, I can't find it.
>>
>> Does anyone remember this thread within the last 3 or 4 months ???
>> If not,can any recommend how to cook these tubes in ???
>>
>> TNX es 73
>> Bob, K1VU
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
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