[Amps] Peter Dahl / Harbach SB-220 transformer

[Jim Thomson]

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