[Heathkit] reactivation of a 3-500

[Garey Barrell]

Paul -

Yes, that is possible also.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>

Paul Kraemer wrote:
> What about just disabling the hv for testing
> That is what I have done with amps I worked on
> If the plate connections are pulled you have a makings of a test box and can sub in a low 
> voltage supply to make the tubes draw plate current
> Can't you?
> Paul K0UYA
>
> --------------------------------------------------
> From: "Garey Barrell" <k4oah at mindspring.com>
> Sent: Friday, May 16, 2014 1:53 PM
> To: "Chris Kepus" <ckepus at comcast.net>; "Heathkit Reflector" <heathkit at mailman.qth.net>
> Subject: Re: [Heathkit] reactivation of a 3-500
>
>> Chris -
>>
>> The best way if you can, is reduce the PLATE voltage somewhat. Hopefully your amp has a 
>> current limiting resistor in the HV, and protection for the meters in case of an arc. One 
>> problem is that tubes that have been idle for a while often arc over when HV is applied, and 
>> this can cause damage to things other than the tube.  The Grid is in this path, so don't 
>> forget the Grid meter protection.
>>
>> Then you have to apply some positive voltage to the Grid to make the tube draw more than it's 
>> 'zero-bias' current and thus heat up the PLATE.
>>
>> Ideally, you'd have a separate test setup with a socket, air and a high voltage supply.  Most 
>> of us can't do that however!
>>
>> I've done two sets of tubes in my L-4B with no difficulty.  I first let them run for a couple 
>> of hours with just filament current.  I don't think this serves any purpose, but made me feel 
>> better!  :-)  I applied CW high voltage, only about 1700 V in the L-4B and tuned it up.  I 
>> have a four foot long dummy load with a large fan on one end that was able to dissipate the 
>> RF generated.  I let them run for two hours at a dull red color, and that did it.
>>
>> If you can't do that, you can lift the filament transformer center tap and apply a positive 
>> voltage of I think about 40 VDC.  I don't remember for sure, and can't find my notes. Adjust 
>> the voltage until the plates glow a dull red at IDLE and wait.
>>
>> EIMAC discovered back in the 30's that their tubes lasted longer when 'run hard' i.e., red 
>> plates, in commercial service, than they did when tubes were operated with no color.......   
>> The plates were made of tungsten then, which 'getters' very well when "HOT".....  After the 
>> war, tungsten was too expensive so they came up with 'Zirconium' which when plated on tube 
>> plates also performed 'gettering' when hot.
>>
>> 73, Garey - K4OAH
>> Glen Allen, VA
>>
>> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
>> and TR-4/C Service Supplement CDs
>> <www.k4oah.com>
>>
>> Chris Kepus wrote:
>>> Garey,
>>>
>>> Excellent points, to be sure.
>>>
>>> Couple of questions. If one has a dual 3-500 amp that hasn't been fired up
>>> in years, it is reported all over the web that the 3-500 doesn't do well if
>>> kept in storage for extended periods. It could be a very unpleasant and
>>> expensive event when the amp is once again fired up. How does one avoid
>>> damage to the amp but accomplish what you described with your 3-500s? (if
>>> this is already written up, please direct me to the reading room).
>>>
>>> Assuming the tube(s) don't short and arc over at start up, and assuming
>>> there's an answer to the above question, what dummy load does one use that
>>> won't cook during this hour plus long plate heating process?
>>>
>>> Thanks es 73,,
>>> Chris
>>> W7JPG
>>>
>>>
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: Heathkit [mailto:heathkit-bounces at mailman.qth.net] On Behalf Of Garey
>>> Barrell
>>> Sent: Friday, May 16, 2014 7:52 AM
>>> To: Ulrich Graf; heathkit at mailman.qth.net >> Heathkit Reflector
>>> Subject: Re: [Heathkit] reactivation of a 3-500
>>>
>>> Uli -
>>>
>>> The 'heating' must be more than just the filament.  You need plate
>>> dissipation.  The plates need to be heated to red hot for some period of
>>> time.  IF these are EIMAC tubes there is a coating on the plates that is
>>> 'activated' by red heat.  I have had tubes recover after only an hour at red
>>> heat.  Be sure and keep air going, especially on the glass/metal seams of
>>> the pins and plate cap..
>>>
>>> 73, Garey - K4OAH
>>> Glen Allen, VA
>>>
>>> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
>>> and TR-4/C Service Supplement CDs
>>> <www.k4oah.com>
>>>
>>> Ulrich Graf wrote:
>>>> Hi to the list,
>>>>
>>>> got an SB-1000 linear amplifier recently second hand. While activating
>>>> PTT I noticed that the bias current is continuously increasing. Bias
>>>> network seems to be ok. So the tube must have drawn some gas. How can
>>>> I activate the getter the easiest way to reuse this tube again? Many
>>>> hours of heating do not work.
>>>>
>>>> vy 73, Uli, DK4SX