[Amps] New SB-200 owner

[Roger Halstead]

>
> In a message dated 9/26/2007 8:14:05 P.M. Eastern Daylight Time,
> sub1 at rogerhalstead.com writes:
>
> Were it  me, I'd start with a search for articles on such conversions. 
> They
> may or may not be on the net. I don't recall seeing any in the ham
> magazines, but I wasn't interested in doing a conversion until  recently. 
> As
> I recall the ARRL Handbook and amplifier books deal  with complete builds. 
> I
> don't know about QEX.

I wonder about going the 4CX-250 route, or 4-250. Apparently my Eimac hand 
book is out in the shop so I can't look up the numbers for the 125, 250 and 
400, but I do have a commercial 2-meter amp using a pair of 4-125s and I'd 
guess the 4-250s may go that high. the 4-400s? they are as large as a 3-500Z 
and maybe a tiny bit taller. If they'd go to  50 MHz (which I think they 
will) they might make a whale of a 6-meter amp in an SB 220 case, but as I 
recall the 4-400s are a bit more pricy than the 125s and 250s or even the 
4CX250s and a *lot* more than 3-500Zs .  They'd fit  with the possible 
exception of the 4-400 and are of a relatively good price. the 4CX 250s were 
widely used in VHF amps as well as HF (re the old KWS-1 which I had and the 
collins 6 & 2 transverter) IIRC the 4CX-250s will mount in any position and 
should give 600 to 800 out for a pair. Yes they would take a screen supply 
but a relatively simple one that should easily fit in the space freed up by 
going to the smaller tubes. There'd also be space for a plenum for the tube 
sockets and a blower.  Of course I remember the old KWS-1 was a great space 
heater for my shack in the winter, but a good part of that came from the 
75A4 and exciter portion of the KWS-1.  . OTOH my old Henry 2K-4 really 
throws out a lot of heat.  With the 3-500Zs having a typical gain of 10 db I 
keep wondering how some are claiming 1500 out with only 75 watts of drive. 
It takes me a 100 to get 1200 out and I could use it for a coffee warmer 
while doing it. Coffee warmer? I could cook dinner on it.

I realize I've gone from a tank circuit conversion to a major change, but 
isn't that what ham radio is all about, or is for at some of us.

73

Roger (K8RI)

>
>
>
> To my knowledge there has not been a conversion published on the Sb-200 
> that
> I believe is worth trying.  I tried them in the beginning, found I had  to
> blow on the dials when tuning up so I can find "the sweet spot" for 
> everything
> to come together, but then, there are some that will be satisfied  with 
> that.
> What really needs to be done is to take a tried and true  amplifier 
> design,
> such as the many written for 6 meter 3CX800 and 8877 tubes and  simply 
> adapt it
> to the Sb-200.  When the same principles are incorporated  properly to the
> Sb-200, you can and will have a nice easy to tune amplifier for  6 meters. 
> You
> will notice if you have any experience with an HF SB-200,  that it will 
> load
> very smoothly on 80 and 40 meters, when you get to 10 meters  it gets 
> pretty
> critical, can you imagine the tuning of the same amp at 50mhz if  all the 
> same
> components are used?  Not too good, yet 85% of the trash you  will see on
> SB-200 conversions is exactly that, add on 6 meters to HF.  Do  a good 
> sound 6
> meter only conversion and you will be a lot happier.  No  voodo magic 
> needed.
> Good luck 73 Lou
>
>
>
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