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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