[SixClub] SB-200 6 meter conversions

Roger (K8RI) 50mhz at rogerhalstead.com
Mon May 24 21:19:37 EDT 2010


On 5/24/2010 10:02 PM, kd4e wrote:
> Nice piece of work!
>
> I have a GI-6b that I believe is identical to the GI-7b
> except not good up into the 2m and above range - fine on
> HF and 6M.  $35. including std USA shipping.
>
> doc
>
> KB0NLY wrote:
>    
>> I had an amp on 6m running 572b's, while it would make
>> power it seemed to oscillate and tuning was very touchy.
>> After a while of fighting it and talking to many other
>> conversion owners I determined it was the best I was
>> going to get out of it.  The tubes just aren't worth a
>> darn at 6.  They glow red at 10m, pushing them higher in
>> frequency they would look hot enough to melt.  I tried a
>> new set of tubes, Taylor 572b's, and they did a little
>> better, some more mods and adjustments helped some of the
>> problems.  Eventually I got fed up with it and sold it.
>>
>> I then had the opportunity to operate a station that used
>> a SB-200 converted to a single GI7BT russian triode.
>> Tuning was nice, clean output, very stable and easy to
>> use.  I decided to build my own but couldn't get an
>> affordable candidate for parts by this time.  I ended up
>> finding a Yaesu FL-2100B that was damaged while being
>> shipped, the meters smashed, a small dent on one back
>> corner of the case.  I bought it and started to gut it
>> and rebuild it.  A couple months of weekends later I had
>> a half gallon amp that is very user friendly.
That PS should handle apair of those IIRC.
>> have one thing I would like to improve on it and that's a
>> fan upgrade, the current AC fans In there are pretty low
>> flow and I want to swap out for one or two higher output
>> muffin fans.  However in its current configuration it
>> doesn't get too hot to concern me.  I usually only push
>> it to about 300w for casual use, though I have driven it
>> to 500w a few times.
>>      
Some where on the net is a photo of one with a squirrel cage fan on the 
back, pressurizing the under side of the tube compartment.  It's a very 
neat and clean modification. I saw an MLA 2500 conversion using a pair 
of the FI-7B's. it ran around a KW out and also had the same fan 
modification.
>> http://kb0nly.info/6mqro.html
>>
>> One of these days I think I might actually get
>> adventurous and build an amp using a pair of GI7BT's and
>> see if I can get a full gallon out of them.
>>      
You might want to look at the GS-31B. It's rated for a KW with a much 
larger heat sink.  $49 each.1.2 KG with heat sink. Good from 5 MHz to 2 
GHz.I think, but not sure,  the bottom is the same as the GI-7B
Some with machine shop access have removed the heat sinks from both the 
GI7B and the GS-31B, and build a brass water tank and used water 
cooling.  You still have to put air on the seals, but just think...a big 
amp with no fan noise.

73

Roger(KI8RI)
>> 73,
>>
>> Scott KB0NLY
>>      
>    



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