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Author Topic: SB-221 mods  (Read 447 times)

KB0FXA

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SB-221 mods
« on: February 25, 2023, 11:59:51 PM »


Been thinking about adding 10 meters to this amp, it works great, input SWR on 10 meters is fine, no output, I didn't see it on the print, I downloaded the prints for the SB-220 and SB-221, there has to be a filter not passing the signal, I just didn't see it on the prints, I looked up the mods on 73 magazine, sure miss that, shows plate choke Barker & Williamson 801, Barker & Williamson filament choke FC-25A, and Barker % Williamson tank coil 195-3, I can find some choke coils that are close, will I have to wind the plate tank coil?  Last I checked the wafer sections for the band switch were available to take this amp from 160 to 10 meters.
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WB8PFZ

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Re: SB-221 mods
« Reply #1 on: February 26, 2023, 03:20:35 AM »

There was a trap on the input that was in a sealed aluminum box. The output coil needs to have a tap installed for the 10 meter band. Should be all you need to do.
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W1QJ

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Re: SB-221 mods
« Reply #2 on: February 26, 2023, 03:44:19 AM »

The sb221 tank band switch and input switch do not have contacts on them for 10 meters. There is  no 10 meter input circuit and there is no tap to the tank coil for 10 meters.  The switch doesn’t even turn to a 10 meter position.  Not to mention there is a filter for that frequency in line.  To put an sb221 on 10 meters you need all the missing parts.  Requires lots of work.  The easy way is to install a full L chassis network from an SB220 and be done with it.
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PE1HZG

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Re: SB-221 mods
« Reply #3 on: March 05, 2023, 01:17:50 PM »

From https://puck.nether.net/pipermail/heath/2010-March/025575.html :

From Robert Groh
Wed Mar 31 20:38:32 EDT 2010

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

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W1QJ

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Re: SB-221 mods
« Reply #4 on: March 09, 2023, 04:26:43 AM »

Yeah, he did so many things to disable 10 meters that he can’t remember just what he did.  Somebody wanted to make sure they never got used on 10/11.  Ameritron grounded the input signal.  Snip that wire and presto you are on 10.  The dude from Heath must have really hated CBers.
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VE7RF

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Re: SB-221 mods
« Reply #5 on: March 09, 2023, 05:13:21 AM »

Yeah, he did so many things to disable 10 meters that he can’t remember just what he did.  Somebody wanted to make sure they never got used on 10/11.  Ameritron grounded the input signal.  Snip that wire and presto you are on 10.  The dude from Heath must have really hated CBers.

It gets worse, with that stupid LP filter installed, with it's cut off at 25 mhz, or just  a bit higher, the LP filter interacts with the 4 x tuned inputs on 80-40-20-15m. The values of the C1 + C2 caps are all different on the SB-221  vs the SB-220.

To get it to work on 10m, the LP filter would have to be removed, then change the 15m tap to a 10m tap on the main tank coil.   The install 10M tuned input values (including coil and both caps)  from the SB-220.  Then re-tweak the cap values on the 80-40-20m tuned inputs.  After that is all done, you have 10m... but lost 15m. 

Just to reiterate, it only has a 4 position bandswitch...for both the tuned input..and the main kw output.
« Last Edit: March 09, 2023, 05:18:18 AM by VE7RF »
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KM4AH

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Re: SB-221 mods
« Reply #6 on: March 09, 2023, 09:11:39 AM »

In the meantime CB'ers were building amps with six 3-500Z's in that time period . Pair of 3X3's at least now.

I don't know any CB'er who had any interest in a SB220 or 221.  But, if they did they would yank all that crap out and make a monoband amp.
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N8YX

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Re: SB-221 mods
« Reply #7 on: March 09, 2023, 09:41:08 AM »

In the meantime CB'ers were building amps with six 3-500Z's in that time period . Pair of 3X3's at least now.

I don't know any CB'er who had any interest in a SB220 or 221.  But, if they did they would yank all that crap out and make a monoband amp.
I saw more that a couple running 2x 8877 in a mobile setup way back when. And yes, there are still a number of "11M" SB-2xx amps to be found at most of the larger 'fests. These days the crowd uses them as drivers.
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VE7RF

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Re: SB-221 mods
« Reply #8 on: March 09, 2023, 10:07:44 AM »

In the meantime CB'ers were building amps with six 3-500Z's in that time period . Pair of 3X3's at least now.

I don't know any CB'er who had any interest in a SB220 or 221.  But, if they did they would yank all that crap out and make a monoband amp.
I saw more that a couple running 2x 8877 in a mobile setup way back when. And yes, there are still a number of "11M" SB-2xx amps to be found at most of the larger 'fests. These days the crowd uses them as drivers.

Check out BBI's latest u tube video..where he gets 3300 watts pep out of a 2 x 3-500Z  henry amp.  On SSB, he buries the plate meter to the peg.  300 ma on idle, way too much grid current too. Folks on 11m are nuts.  On AM, his average plate current was no where near what it was on ssb....but pep is the same. 
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KM4AH

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Re: SB-221 mods
« Reply #9 on: March 09, 2023, 02:36:42 PM »

Well, you can trace all of that back to the government with their expected incompetence taking 11 meters from hams and giving it to Citizens Band since obviously 11 meters doesn't "skip".
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