[Heathkit] reactivation of a 3-500

[Garey Barrell]

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
>>
>