[Amps] SB-220 reliability and tuning

[Pete Smith N4ZR]

This puzzles me.  My SB-220 has run for 12 years of CW contesting (in 
the SSB position), with only minimal problems. 1200 watts out on 80, 
down to about 1000 on 10.  I added the Harbach high-volume fan, as well 
as a home-brew vacuum relay T/R system, and have a muffin fan above the 
tube compartment to help by drawing air out.  I polished the filament 
pins and the mating socket clips, after resoldering filament pins a few 
times.

Power supply components are all original.  Tuning is easy on the low 
bands, and even on the high ones I can get close enough in a quick band 
change that I don't risk the hardware before I can tune (using CW 
dits).  My secret?  An index card stuck to the panel behind the tune and 
load controls, with lines for each band.  No turn counters or verniers 
required.

73, Pete N4ZR
The World Contest Station Database, at www.conteststations.com
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On 9/10/2012 9:44 PM, Jim Thomson wrote (in part):
> I wouldn’t be tuning up any SB-220 or L4B with a 800 ma dead cxr any time soon.
> Nor any ameritron 811a  amp nor their AL-80B amp, etc.   That stuff is designed for  ssb,
> low duty cycle use, including tube cooling, tubes, xfmr etc, etc.
>
> ### I use turns counters that have a 0-100 scale on the skirts.  Not only can I dial up
> a particular turn,  I can divide each turn into 100 increments.  Now that’s on HB amps,
> with vac tune + load caps.   A buddy recently  retrofitted jackson bros  6:1 verniers
> into his SB-220, for both tune and load.   They are calibrated 0-100  across the upper
> 180 deg arc of each skirt.   That mod alone, makes tuning the sb-220  a heck of a lot easier,
> esp on the upper bands.