[AMPS] Re: ALC question

[Rich Measures]

>...I only acquired my first amp about a week ago...a
>previously loved AL80A (single 3-500Z), so please bear with me if these are
>dumb questions.
>
>I, too, was wondering about Jeff, K4JNY's question about whether or not to
>leave the amp running. After reading Rich's referenced January 1994 QST
>article, "The Nearly Perfect Amplifier" I'm not sure if I know the answer
>although I think the step-start circuit would be kinder to the tube
>elements.

The primary issue is loss of emission.  Operating the filament/cathode at 
more voltage than is necessary to achieve normal output results in a 
E2/E1^23.44 decrease in useful life of the tube.  For a healthy 3-500Z, 
4.8v on the filament is about right.  I know of several models of 3-500Z 
amplifiers which use c. 5.8v on the filament.  The result is 1/84 - or 
1.2% - of the potential useful life.  
>
>However, towards the end of Rich's article, another issue arose which has
>been perplexing me:
>
>Do you need to connect the ALC line between the amplifier and the 
>transceiver?

Not necessarily.   The trade-off with ALC is leading edge splatter on 
SSB, which is perfectly acceptable according to FCC rules.  
>
>The vendor of my used amp said he never used it...he just made sure he was
>within the ALC on his transceiver. Others have told me that they would
>never use an amp without the ALC connection.

With a delicate oxide-type cathode, ALC reduces the chance of stripping 
the cathode coating due to over drive.   However, the tungsten-carbide 
emissive coating on a thoriated-tungsten filament can not be stripped.  
>...snip...
Rich---

R. L. Measures, 805-386-3734, AG6K   


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