Date: Fri, 11 Jun 2010 07:27:04 EDT
From: Gudguyham@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@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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