SB-221 10 meter mod.

[Robert Groh]

Mark,  I was the engineer who did the dastardly deed of designing the conversion of the SB-220 to the SB-221.  It has been a long time but, as I remember it, the changes were as follows:
1.  Replace the bandswitch with 4 position bandswitch (a relatively stupid recommendation on my part - way more than was needed but that is water over the dam).  Remove the 10M tank coil and connections
2.  Add the LPF so you couldn't drive it on 10M.
3.  Here it gets fuzzy - I think I had to made some minor (i.e. cap changes) to the input tuning networks to get the input VSWR back.

At any rate, I would carefully examine the two schematics - it should be relatively clear on what was changed.  There aren't that many parts to begin with!  We didn't change any of the mechanical parts arrangement, etc other than those mentioned.

Best of luck - a very nice amplifier and well regarded by the ham fraternity.  Just don't try to get too much out of it!

73
Bob Groh, WA2CKY
Principal Engineer, Ham Radio Group, Heathkit, 1977 to 1981




________________________________
From: mark oldag <lahainamark at YAHOO.COM>
To: HEATH at LISTS.TEMPE.GOV
Sent: Wed, March 31, 2010 3:59:11 PM
Subject: [HEATH-TEMPE] SB-221 10 meter mod.

Aloha, All     I hope the day is going well. I have a sb-221 that I have almost
totally refurbished i.e. new load capacitor all the Harbach mods and
including just this weekend a new filter cap block. Problem is that I
want more. I want 10 meter capability. I have a Hy-gain 105c 5 element
mono beam on a tower with a rotor and no amp. Furthermore I have a 10-80 band
switch complete with caps and coils from an old sb-220, I have the back wafer  that connects to the tank/coil coming from Harbach, I have both complete sb-220 and
sb-221 construction manuals. The problem is I cant find any info on the
conversion in verbal or diagram form. I know that the CB filter needs
to come out and has. Am I missing something or do I have enough info to
do the job right? Dos anybody  have any additional diagram or text
support that they can offer? Thanks for your time!  Aloha Mark Oldag
WH7TU.  email:  oldagm001 at hawaii.rr.com




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