I have the same Eimac tubes in my LK-500ZC that I got new in 1986. They have
been run hard in scores of contests and DX pileups.
The reason for the longevity is that they are driven with only 80-85W for
1200W out, the filaments at 4.8V key down (never mind the asinine recent QST
article), and the anodes are run a dark orange on a regular basis..... this
is since new. These days the anode color is mostly done as an AM linear
using a TS-940 or TS-950SD.
Carl
KM1H
Sent: Sunday, November 06, 2011 2:21 PM
Subject: Re: [Amps] Gettering 3-500 Tubes
>I can agree with that.
>
> Although I don't usually let the 3-500s sit for more than a couple of
> years.
>
> The ones in my Amp Supply LK-500ZB are the originals.
>
> When it was shipped to me in the late '90s, The tubes were sent in a
> separate box in there original Eimac packaging.
>
> I still fire it up on AM with a DX-60/HG-10 feeding it. Does nicely on
> AM.
>
> The Amp Supply does NOT use air sockets or chimneys. However, it is
> indeed built like a tank, and has one healthy muffin fan that cools it
> all.
>
> Unlike Heath, Amp Supply used top line parts. The transformer was made by
> PW Dahl.
>
> Bob - N0DGN
>
> On 11/6/2011 1:30 PM, Dave White wrote:
>> Great advice as ever from Carl. Print it out and pin it on the shack
>> door :-)
>>
>> Dave G0OIL
>>
>> ----- Original Message -----
>> From: Carl<km1h@jeremy.mv.com>
>> Sent: 06 November 2011 02:16
>> To: rbethman<rbethman@comcast.net>; amps@contesting.com
>> Cc: R Johnson<rjohnson@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@comcast.net>
>> To:<amps@contesting.com>
>> Cc: "R Johnson"<rjohnson@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@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>
> --
> +------------------------------------------------------------------+
> | AM Amateur Radio Operator NØDGN |
> +------------------------------------------------------------------+
> | http://home.comcast.net/~rbethman/ |
> +------------------------------------------------------------------+
> | Bob Bethman \\\|/// " The absence of a danger |
> | \\ ~ ~ // signal does *NOT* mean |
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> +----------------------o00o---°(_)°---o00o-------------------------+
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>
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