[Amps] SB-220 6M conversion
Manuals at ArtekManuals.com
Sat Jun 6 13:19:04 EDT 2020
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
> ## 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
> ## 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
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
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