[Amps] input matching question on the YC156?

[R.Measures]

On Sep 16, 2004, at 9:54 PM, Leigh S. Jones wrote:

> Neil
>
> I can't imagine that this has gone on all day and no one has told you.
> I may get a little heavy handed here.  Sorry in advance.  Applying
> drive power without pre-heating the filaments is not allowed for this
> tube.  I'm not an Eimac employee, but I have read the 3CPX5000A7
> data sheet.
>
> Two simple rules:
>
> rule 1: never apply plate voltage to the tube nor apply drive power
> until after the prescribed filament warm-up period has elapsed
>
Hello, Leigh -- Drawing cathode-I before a proper warmup can strip the 
barium-oxide and strontium oxide coating off of a heater-type cathode.  
Applying anode-V to a heater-type cathode that has cut-off grid-bias 
applied causes no damage because no cathode-I can be drawn in the 
cut-off state.  OTOH, the vast majority of filament-type (thoriated 
tungsten) cathodes can safely provide current during their 
approximately 1-second warmup period because the tungsten di-carbide 
emissive layer is epitaxially bonded to the thoriated tungsten beneath.

> rule 2: never apply drive power until plate voltage has been applied

> details:
>
> 1) apply forced air cooling
> 2) apply filament voltage
> 3) delay according to tube manufacturers instructions

A retired Eimac engineering department employee told me that an 
additional 30-seconds of warmup above the stated spec is not a bad idea 
since the marketing department was constantly trying to push specified 
warmup times lower than the engineering department wanted.
-  To observe how much warmup time a heater-type cathode requires, 
connect a DMM between the cathode and the grid, apply heater power 
(only) and measure the potential  as the cathode warms up.  When the V 
stops increasing, the cathode is warmed-up.
.
> 4) apply plate voltage
> 5) connect antenna switch
> 6) allow cathode current (bias to operating level)
> 7) apply drive power to transmit
> 8) stop applying drive power
> 9) bias to cut-off cathode current
> 10) disconnect antenna switch
> 11) repeat steps 5-10 in order as many times as needed
> 12) remove plate voltage
> 13) remove filament voltage
> 14) delay according to tube manufacturers instructions
> 15) remove forced air cooling
>
> Sorry if this sounds like me preaching to you, but someone has
> to tell you.
>
> KR6X
>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org