[Amps] Peter Dahl / Harbach SB-220 transformer

[James Colville]

The SB-220 band switch is a shorting type.

73
Jim W7RY


On Sat, Jun 12, 2010 at 2:06 AM, Jim Thomson <jim.thom at telus.net> wrote:

> Date: Fri, 11 Jun 2010 07:27:04 EDT
> From: Gudguyham at aol.com
> Subject: Re: [Amps] Peter Dahl / Harbach SB-220 transformer
>
>
> In a message dated 6/11/2010 7:10:20 A.M. Eastern Daylight Time,
> jim.thom at telus.net writes:
>
> ##   It works good on 80-40- 20-17-15-12-10m.    Heck, it even works very
> good  on SB-220's... that have been modified for 6m.
>
> I actually stopped directly grounding the grids on my 6 meter conversions
> to limit the power output (like a governor) once I was able to obtain
> 1500PEP  output with indirectly grounded grids.  In the beginning when I
> was
> looking  for that "missing" power I would purposely ground the grids to
> boost the
> gain  and the power.  But later when I refined everything and found other
> ways to  obtain the power, I left the grids indirectly grounded. It is
> actually quite  surprising the additional gain you get from directly
> grounding the
> grids.
>
> Lou
>
>
> ## what other ways did u employ.. to get the power up..or more eff ?  The
> best we could
> cook up on that 2 x GS25B  6m amp  was to dump the T network.. and use a PI
>  tuned input.
> Optimum tubing coil used on output.  1st 6m amp  would cook the air
> variable load cap.. so it was dumped
> in favour of a  vac cap on 2 x holer version.   Vac tune cap used on both
> the single and 2 x holer.   Eff was
> very good.    Strap, laid flat, works good for a 6m tank  coil, then no
> stray C between turns.
>
> ## tapping the tank coil in the middle  to make a  'L-PI'    will work too
> on the single tube... but wasn't
> used on the 2 x holer.
>
> ## That bandswitch on the SB-220 is flaky as is..stock.  It's a non
> shorting type... which doesn't help matters.
> The bandswitch  in the L4B  looks flaky enough to me. It has a solid
> detent... but the switch contacts are still not
> huge.. and not paralleled.. like a SB-220.
>
>
>
>
>
>
>
> ##  A buddy across town  built a single 3-500z  for 6m.. works good... abt
> 500w .   He wiped out the neighbourhood
> CATV... and that amp was relegated to FD use.  He also wiped out the 49.9
> mhz  cordless phone freqs at the time.  This
> was 10 yrs ago.
>
> later.... Jim  VE7RF
>
>
>
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