[Heathkit] reactivation of a 3-500

Fri May 16 16:21:39 EDT 2014

Garey, you are EVERYWHERE, aren't you? :D

The way I've done it with my Drake amps is to key the amp in low power (CW)
mode with NO drive. After a short while the plates will start to glow red from
just the idle current. I hold it keyed until I think they are approaching too
red (a subjective call) and allow a cooling period. Rinse and repeat.

73

-Jim (ok, don't really rinse....)
NU0C

On Fri, 16 May 2014 14:53:38 -0400, Garey Barrell wrote:

>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
>>>
>>
>
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