On Tue, 30 Sep 97 03:42:17 -0800 Rich Measures <measures@vc.net> writes:
>>...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
I've been away 9 days so probably missed some of this discussion since my
ISP has a limited message buffer. I'll keep it short.
The AL-80/SB-1000 will be driven into splatter conditions with 100W of
drive and no ALC. Splatter only affects others on the band and on
frequency great sounding signal reports are meaningless.
A 3-500Z requires only 65W of drive to reach FULL RATED output. For the
above amps the proper procedure is then to load it to maximum output with
100W of carrier.
On SSB use the mike gain control to limit voice peaks on the meter to
200ma, 250-275ma if using a processor. This will actually be 400ma peak
which is the tube manufacturers spec.
Done this way you do not need the ALC line which has its own problems.
Always follow the tube specs first...the rest is manufacturers
advertising dreams.
73 Carl KM1H
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