[AMPS] SB-220 standby switch

[Chris R. Burger]

I see terms like "unjustifiable" being used in connection with the 
proposed standby switch on the SB-220.  However, there's a different 
angle.

To say that turning a 3-500Z on and off a few thousand times has 
absolutely no impact on its lifetime, is ludicrous.  While I would 
agree that the impact is probably limited if inrush limiting is 
provided, there is an undeniable link between operating cycles and 
lifetime.  

Also, several posts have mentioned (without specific explanation 
that I noticed) that the HV must be on the low setting to ensure that 
the tube lifetime is not jeopardised.

If we accept that there is some need to limit on/off cycles (which 
seems reasonable to me), the next step is to assess the number of 
cycles that are likely to result in 'normal' operation.  And this is 
the point of this post.

For some, 'normal' operation may involve a daily sked, or casual 
operation on an irregular basis.  Under these conditions I'd agree 
that a standby switch is senseless.

However, other interest groups have very different demands.  For 
example, I am a contester.  In a contest, I may make a dozen band 
changes within twenty minutes.  Probably the most common situation is 
where a potential multiplier is being dragged from band to band.  
Such situations may account for literally hundreds of band changes on 
a single weekend.  In the interests of time, I often don't re-tune 
the amplifier on the new band, and simply bypass the amp to work the 
station with the exciter only.  This habit saves literally hundreds 
of re-tunes per contest.

However, in the SB-220, it would also add literally hundreds of on-
off cycles on the tubes in a single contest!  Most of these would be 
with the HV switch in the high position, too.

I do believe that a standby switch is a good investment under these 
circumstances.  Even if your tube life is only extended by 5%, that's 
a saving of $ 10 per set.

A way of getting around the requirement for panel modification is to 
use an in-line reading lamp switch in the PTT line.  Alternatively 
(and this might present ergonomic advantages) a simple switch mounted 
on a little instrument enclosure would work just as well.

A few minutes of effort, probably two bucks in materials, and there 
you go.  Unjustifiable?  I think not.


Chris R. Burger
ZS6EZ

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