Oops, forgot to mention, my plate tank for 6m (SB-220 mod) is 3-1/2 turns of
1/4" copper tubing on a 1-1/2" diameter form (inside diameter of the tank
coil); plate TUNE cap is 2-30 pF Jennings vacuum variable, either 5kV or
7.5kV (either model seems to work); plate LOAD cap is the original TUNE cap
from the SB-220. I don't re-use any of the original tank circuitry at all,
except for the old TUNE cap, which I re-use as the new LOAD cap for six.
WB2WIK/6
"There is no reason anyone would want a computer in their home." - Ken
Olson, Chairman & Founder, Digital Equipment Corporation (1977)
> -----Original Message-----
> From: Steve Katz
> Sent: Wednesday, August 18, 2004 11:12 AM
> To: 'Manuel "Teknik forumet"'
> Cc: 'amps@contesting.com'
> Subject: [BULK] - RE: [BULK] - [Amps] Convert Heathkit SB-220 to
> 50Mhz
>
>
> Manuel,
>
> I'd suggest you go ahead and try that, but in my experience, that's a
> lousy
> modification. It assumes you're sacrificing only the 10m band for 6m, and
> leaving the other bands intact, including the bandswitch and its wiring,
> with its parasitic reactance. I've never found that to work efficiently
> or
> in a stable manner on six meters, but you can certainly give it a try.
>
> My SB-220 mods sacrifice the amp for six meter operation only, and I get
> rid
> of the bandswitch altogether. It's the only way I've found to make it
> work
> with full-time stability and high efficiency (900W output power at 50
> MHz).
>
> WB2WIK/6
>
> > -----Original Message-----
> > From: Manuel "Teknik forumet" [SMTP:manuel@limmared.nu]
> > Sent: Wednesday, August 18, 2004 11:31 AM
> > To: Steve Katz
> > Subject: SV: [BULK] - [Amps] Convert Heathkit SB-220 to 50Mhz
> >
> > Hi
> > Thank´s for this information.
> > I have found a lot of mods, but nerly evryones are like
> > 1) Move the 10-meter tap on the plate coil (L6) to a point 1-2/3 turns
> > from
> > the plate-tune capacitor. A grid-dip oscillator can be used to check
> > resonance at 50 MHz.
> > 2) Unwind the 10-meter input coil (L1), leaving 2-3/4 turns.
> > 3) Replace C33 and C34 by a single 10 pF mica capacitor.
> > 4) Change C35 (115 pF) to a 33-pF mica capacitor.
> >
> > Manuel SM6TMR
> >
> > -----Ursprungligt meddelande-----
> > Från: Steve Katz [mailto:stevek@jmr.com]
> > Skickat: den 18 augusti 2004 19:44
> > Till: 'Manuel "Teknik forumet"'; Amps@contesting.com
> > Ämne: RE: [BULK] - [Amps] Convert Heathkit SB-220 to 50Mhz
> >
> > Manuel, is nobody answering you on this?
> >
> > I don't know what conversions you've seen, but I've converted three
> > SB-220s
> > to six meters over the years, and each the same way. In all cases, I
> got
> > rid of the bandswitch entirely and used that hole to mount a 2-30pF
> vacuum
> > variable capacitor; got rid of the LOAD cap entirely and used the
> original
> > TUNE cap as the new 6m LOAD capacitor; re-wound the plate RFC with many
> > fewer turns (only need about 1/4 the original winding length for 6m);
> > eliminated the original bandswitched input networks and replaced them
> with
> > a
> > single network for 6m only; added more front panel grounding (aluminum
> > bracket) for the new plate tune & load caps (the inductance via the
> front
> > panel is too high); replaced the original parasitic suppressors with new
> > ones having the carbon resistor soldered across 1/2-turn of copper 1/4"
> > wide
> > strap; stuff like that. The conversion takes about one full day (8
> hours)
> > and works well.
> >
> > With good tubes, I get about 900W output on six. The original T-R relay
> > isn't the greatest on 50 MHz, and I often go to a conventional Dow-Key
> > dual-pole coaxial relay like the DK-260 to pick up about a dB or so in
> > performance (even on receive). Of course, I add the "standby switch"
> mod
> > and also the "low voltage keying mod" to any SB-220 before I even get
> > started!
> >
> > Are you familiar with this stuff?
> >
> > 73 de Steve WB2WIK/6
> >
> > "There is no reason anyone would want a computer in their home." - Ken
> > Olson, Chairman & Founder, Digital Equipment Corporation (1977)
> >
> > > -----Original Message-----
> > > From: Manuel "Teknik forumet" [SMTP:manuel@limmared.nu]
> > > Sent: Wednesday, August 18, 2004 10:52 AM
> > > To: Amps@contesting.com
> > > Subject: [BULK] - [Amps] Convert Heathkit SB-220 to 50Mhz
> > >
> > > Hi
> > >
> > >
> > >
> > > Have get a Heathkit SB-220 and like to convert it to 50Mhz.
> > >
> > > Have seen different modds on the Internet, so i like to know the best
> > > way to mod this amp?
> > >
> > > Anyone?
> > >
> > >
> > >
> > > Manuel SM6TMR
> > >
> > > manuel@limmared.nu
> > >
> > >
> > > _______________________________________________
> > > Amps mailing list
> > > Amps@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/amps
> >
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