[AMRadio] Old Tube burn-in

[Donald Chester]

 ARS W5OMR <ars.w5omr at gmail.com> wrote:

> I made a pretty decent deal at a recent hamfest - (6) 250TH'S. (4) of which
> are still sealed in their original boxes.

> I pulled the (2) out of their open boxes, and it appears as if they've
> never been twisted into a socket.

> Don/K4KYV, at one time, discussed the pitfalls of running filament voltage
> too high, or too low, per Eitel-McCullough(sp?) specs.

> My concern for these tubes,  after resting for so long, is that they may
> tend to be 'gassy'.

That tends to be a problem with Eimac type tubes.  Graphite anode tubes seem to fare better sitting long time on the shelf.  I once "mined" about a dozen WWII era VT4-C/211s that were buried in the ground after the floor had rotted out in an old timer's storage building. Only two were bad; the rest tested as good as new.

Here's what RCA recommends for breaking in thoriated tungsten filament tubes:



 RCA's Recommended Break-In Procedure for Power Tubes

From Application Guide for RCA power tubes
​
The following "break-in" treatment is recommended for new or used tubes which have been in storage for an extended period, before placing such tubes in service. This "break-in" treatment preferably should be in equipment in which the tube is to be used when new circuits are tested or when adjustments are made.

Step 1: Make sure that the cooling system and protective devices are functioning properly.

Step 2: With no other voltages on the tube, apply voltage to the filament or heater at the prescribed typical operating voltage for 15 minutes.

Step 3: Apply reduced value of rf drive power and grid-No.1 voltage (approximately three-quarters normal drive power) for 15 minutes.

Step 4: Apply reduced value of plate voltage and grid-No.2 voltage (approximately one-half normal values) until stable performance is obtained.

Step 5: Increase rf drive power and grid-No. 1 voltage to normal.

Step 6: Increase plate voltage and grid-No.2 voltage to normal, gradually or in steps. Operate the tube until stable performance is obtained at each voltage level.

After the tube is given the above treatment and is operating normally to give the desired output, it is suggested that the readings of the meters and the control settings be recorded for future reference.



For tubes that have been out of service for several years, I follow the above procedure, but with increased time for each step. I normally run the filament for about two hours (Step 2), then apply reduced grid drive for 30 minutes to a couple of hours (Step 3), reduced plate voltage (Step 4) for 1-2 hours, and finally let the tube run into a dummy load with full grid drive and full plate voltage for a couple of hours.

With questionable tubes, I have been known to run the filament overnight before continuing with the procedure.

Don k4kyv

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