[Amps] 8877 heater open circuit after shipping

[Conrad PA5Y]

Was this intentional or a funny accident?

' This has for many years made it imperative to handle "emergency spare" 
Broadcast transmitting tubes extremely      genitally     , without any bumping.......'

73

Conrad PA5Y



-----Original Message-----
From: Amps <amps-bounces at contesting.com> On Behalf Of Ron W4BIN
Sent: 01 April 2023 17:55
To: amp <amps at contesting.com>
Subject: Re: [Amps] 8877 heater open circuit after shipping

    Alan Ibbetson wrote:
> The guy sent the open-heater 8877 back. Yes, the heater is open and 
> yes, it is the tube I sent him (date code and serial numbers match). 
> So maybe the valve really was broken in transit.

Electrons are produced when the filament wire is heated above 2200 ^o C. 
Adding small
amounts of thorium to the tungsten in the filament wire *reduces this temperature substantially*, to about 1700 ^o C.  This increases the efficiency of electron production and increases the life of the filament wire.

   Unfortunately after many hours of operation the thorium moves around in the tungsten, eventually the molecules align in lines, gradually the tungsten becomes very brittle.
This has for years caused it to be inadvisable to move a tungsten light "bulb" that shows a blackening (even ever so slight) between lamps.  I believe the increase in electron production results from the fact that thorium is mildly radioactive.
Since thorium-232, has a half-life of about 14,050,000,000 years the ability to increase the electron production will not fade over the lifetime of vacuum tubes.

This has for many years made it imperative to handle "emergency spare" 
broadcast
transmitting tubes extremely genitally, without any bumping, when it is time to test and re-degassing.
--
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