[Amps] SB-220 6M conversion

[Artek Manuals]

Jim et All

Replies interspaced below

On 6/6/2020 12:41 PM, Jim Thomson wrote:
> Date: Sat, 6 Jun 2020 09:28:30 -0400
> From: Artek Manuals <Manuals at ArtekManuals.com>
> To: n2ic at arrl.net, "Amps at Contesting.com" <amps at contesting.com>
> Subject: Re: [Amps] SB-220 6M conversion
>
> <Running in the CW position just to be on the safe side ( after all this
> <amp is nearly 40 years old) Going easy on the power transformer. I can
> <only get about 100 more watts in SSB position
>
> <Dave
> <NR1DX
>
> ##  what EXACTLY  are you using to  measure  power output ???
> I have a buddy  with a hb  8877  6m amp.  Eff  was low,  we tried
> every trick in the book...with  small incremental  increases.
> Turns out the   NEW bird slug was way off...on the low  side !
> Use a bird or  coaxial dynamics slug, the  25-60 mhz type, for a
> bird  43  line section.
I have both a Bird 43 with the proper slug and a Kenwood 2000 wattmeter. 
Both of these agree within a few watts When checked against the SB220 
and comparative measuring the output in the same power range from a 
Elelcraft 1500 amp on 6M. Birds by the way are speced only to +/- 5% 
ther are some commercial meters out there that are speced to +/- 3% in 
my experience even that is stretching it ....8^) ....fodder for a 
different thread

> ## Toss those  useless   grid caps...and  ditto  with grid chokes.
> Chassis ground all  6  x grid  pins  with .375 inch wide strap.
> That alone will result in  20-25  watts  less drive required....or
> conversely, more power output for  same amount of  drive you had before.

I will do that next .. I did that with my TL-922A last year did not 
change power out in a meaningful way(but the chassis was in much better 
shape on that amp which led a sheltered life)
> ##  Use a flat strap wound tank coil,  with  at least  .375 inch  wide  copper strap,
> and preferably .5 inch wide  copper strap.

As noted in a item #1 IN THE ORIGINAL POST  both the flat strap tank 
circuit like you suggested ( copied from the King Conversion unit) and a 
portion of the silver plated tubular coil from the original SB220 were 
tried. Absolutely NO DIFFERENCE . Although the Heath-kit coil appeared 
to have a much sharper tuning response ( higher Q?) than the flat strap 
coil. Very subjective observation
> ##  Use a PI net for the  tuned input, with the typ  C1 – L –C2  setup.
> Use  10-12  gauge wire for the  coil on the  tuned input.  When  driven
> full bore,  you should have 1 to 1  input  swr.

As noted in Item #3 IN THE ORIGINAL POST  "3) ) Tried "T" input match. 
Pi input match , straight through ...no difference". I am currently 
around 1.2:1 with a T input network more or less copied from the King 
Conversion.

If you have some specific "L" and "C" values for your suggestion I will 
be happy to revisit the "PI" input version again after I finish doing 
the gris grounds. I am currently around 1.2:1 with a T input network 
more or less copied from the King Conversion

> ##  what did you use for the plate choke ??  10 uh is ample.  You want the
> 1st  series resonance  above  55 mhz.  22 gauge magnet wire  wound on
> teflon or ceramic  will work.

I am using the original Plate Choke as noted in 1/2 dozen articles 
specifically around the SB220 conversion and the again the King 
Conversion uses this choke. I have burned up chokes home brew amps over 
the years due to the resonance issues. The existing plate choke suffers 
no heating under load.

> ##  Dunno about oem parasitic suppressors. I cant see the oem heath suppressors
> working at all on  6m.

Should have been more specific in original post where I said I changed 
the parasitic suppressors. More specifically I am using three 200 ohm 
metal film 3W resistors in parallel with a a copper strap around them , 
again shamelessly copied from the "King Conversion " am

> ## what xcvr are you using for  6M ?  What is the max power out of the  xcvr ?
> How much  grid and plate current..and loaded  B+  do you have on the  SB-220 ?

I use a Kenwood TS890 at the moment. According to the Plate voltage 
meter in SSB mode the plate voltage is around 3000V  going down to about 
2600V under load and I get 750W out Cw. Plate current is on the order of 
500-600Ma and the Grid current is around 150ma. The suspicious thing is 
there is almost no change (other than a slight change in Grid current) 
going from 60W in to 80W input. The improvement in power out from my 
first post was largely achieved through improving the ground connections 
of some of the major components. It will be interesting to see what 
happens when I do the grid ground routine later today

>
> Jim  VE7RF
>

Dave
NR1DX

-- 
Dave
Manuals at ArtekManuals.com
www.ArtekManuals.com


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