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Re: [Amps] SB-220 Plate Tuning Capacitor

Subject: Re: [Amps] SB-220 Plate Tuning Capacitor
Date: Tue, 6 Jun 2006 17:00:24 EDT
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In a message dated 6/6/2006 12:04:30 P.M. Eastern Standard Time, writes:

>From  what Colin told me in a private email, it seems to me that the SB220  
bandswitch is right on edge for the kW input power level, and too small at  
1500 watts for safety. Really needs a bigger one, with a heavier indexing  
mechanism. Now this isw ithout any parasitics, changing band instead of tuning  
anything else. Then there's a problem for people who get arthritis in their  
hands, and that really needs a bar type knob or even a door handle type  
arrangement. I can't say that as a general rule, I particularly like round  
knobs on 
switches - I prefer the bar types such as on the old TU units for the  BC191. 
They also have the advantage that you know immediately if you grab the  
bandswitch.  I believe that's called 'ergonomics'.

Peter  G3RZP

I was really never a Dentron lover and there has been many things said  about 
their amps, but I must admit they did use a much better band switch then  
Heathkit did.  They used pretty much the same switch on all their amps  right 
up to their powerhouse DTR 2000L whose band switch easily handles 1500  watts. 
 I think in the effort of keeping the SB-220 as small and compact as  
possible they opted to use the switch that they used.  I have seen quite a  few 
Supply amps (the new Dentrons)  and I have really never seen a  burned up band 
switch like I have seen with Sb-220's.  Most Dentrons did  not have a tuned 
input circuit but the radios of that era could handle  that.  
Remarkably, the Swan Mark I really was built like a tank and could easily  
handle 2KW if it had the power supply to do so.  B&W built an amp, the  LPA-1 
using  an 850A and some really nice variable caps.  But, they  only ran a pair 
of 813's.  That amp could handle a bunch of power too if it  had a formidable 
PS and tube.
73 Louie
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