[Amps] 8877 filament

[Steven Katz]

How could the current be right on (5V @ 10A) and the tube heater not work?

I've used lots of 8877s and (B+ removed!) if you feel the tube with the heater only on but the blower running, they're cool to the touch and don't get hot at all.   In my experience, not even really warm.   It's only 50 watts, far away from the external anode with a vacuum in between.   The only thing that normally gets slightly warm is the heater pins at the socket.

-----Original Message-----
From: Amps <amps-bounces at contesting.com> On Behalf Of Bob Gibson via Amps
Sent: Saturday, April 1, 2023 3:55 PM
To: amp <amps at contesting.com>; Ron W4BIN <ka4inm at gmail.com>
Subject: Re: [Amps] 8877 filament

The voltage and current are right on..I plugged one of my tubes into same socket and tube heats up fine.. This other tube has a code date of 89 and has YU158 and 3cx1500a7 on it. Anyway I sent the tube back to my friend but I would like to know why it would not heat up..

   73s Bob W5RG
 

    On Saturday, April 1, 2023 at 03:28:14 PM CDT, Ron W4BIN <ka4inm at gmail.com> wrote:  
 
 Bob Gibson via Amps wrote:

> What would cause the filament not to get hot if there is continuity between the pins when 5 volts is applied? The tube has been sitting for seven or eight years.
> Bob

   Measure the filament current.
-- 
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