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To: "W7RY" <>
From: R L Measures <>
Date: Sat, 3 Jun 2006 14:08:06 -0700
List-post: <>
On Jun 3, 2006, at 10:48 AM, W7RY wrote:

> I sure wish Good Guy Ham would sign his emails... (That is just common
> courtesy). It sure would be nice to know who he is.

Maybe he likes to hide in bushes?  Perhaps he has an outstanding  
> The main issue with SB-220 band switches is because of the front panel
> layout, the band switch gets turned instead of the loading control  
> when
> in tune-up mode.

I  do not agree.   Rotating the bandswitch in a properly tuned 220  
results in a reduction in peak-V across the Tune-C and the  
bandswitch.  in my opinion, SB-220 bandswitches typically arc from  
the intermittent parasite at 110mHZ.  The arc is the result of 110MHz  
energy not being able to reach the load through the low-pass tank and  
running amok.
> The very late SB-220s and HL-2200s had longer tune caps. Or Heathkit
> made them available on a replacement basis. I have seen several  
> SB-220s
> with them.

Late Tune-Cs were 4500v-rated instead of 3000v-rated.  The 3000v cap  
would typically arc before the bandswitch arced, but with the new,  
improved 4500v cap, the bandswitch would arc first -- which is not  
good. news.
> 73
> Jim W7RY
> -----Original Message-----
> From: []
> On Behalf Of
> Sent: Saturday, June 03, 2006 10:42 AM
> To:;
> Cc:;
> In a message dated 6/2/2006 5:47:24 PM Eastern Daylight Time,
> writes:
> Finally,  there were some changes made during the SB-220 production
>> run  that may have affected stability; one I have heard of is that
>>  the spacing of the tuning capacitor was increased to prevent
>>  arcing,
> It is NOT my experience that this was ever done.  Every SB-220 I have
> ever
> seen from one of the earliest to the latest always had the same plate
> tune
> variable cap, however they did change the loading cap somewhere along
> the  line.
> Perhaps this is what you meant?
> Speaking of the SB-220 bandswitch.  It always seemed to me that the
> contacts
> on these switches were marginal at best for a 1 KW output amplifier,
> however
> I do believe that Heath designed it as 1KW DC input amplifier (legal
> limit
> at the time).  That said, the manual tune up instructions only called
> for a
> maximum of about 500 mills of plate current.  So at best the output
> would be
> about 500-600watts.  At this rating the contacts may be OK,   
> however we
> all know
> and the reports from others here on the reflector tout their  SB-220's
> going
> 1200-1500 watts output.  That is 2 times the amount Heath  called for
> (according to their loading instructions).  Since I have  autopsied
> dozens of SB-220's
> I have found at least  80% of them had one or  more badly burned
> contacts.
> That's 8 out of 10.  Since the SB-220 has  redundant contacts, many  
> amps
> still
> worked on the bands that had a bad contacts,  but the slightest mishap
> in
> loading (ie too much drive out of resonance) would  result in a  
> nice arc
> at the
> contact since the current capacity of the contact  was now 1/2 what it
> was.
> It is very difficult to examine both sets of contacts on an SB-220 to
> see  if
> they are 100%.  One really needs a small mirror like a dentist uses to
> see
> the contacts and check them for burns.  I'll bet that alot of you out
> there
> who have SB-220's that were bought used probably have a contact  
> that is
> somewhat compromised and does not really know it.  In the same time
> period  there
> where other brands of amps using 3-500's which had MUCH heavier
> bandswitch
> contacts.  I have worked with many of those amps too.  The likelyhood
> of a burned
> bandswitch contact was near ziltch on them.  It is obvious that  many
> run the
> Sb-220 to 800 to 1000 mils of plate current.  In order to  report
> outputs of
> 1200-1500 watts this is surely the case.  The contacts  are simply too
> wimpy
> for that kind of current, especially on the higher bands,  which by  
> the
> way were
> the contacts that were burned.  Most of the time it  was the 10 meter
> contacts that were burned (or totally gone!) then the 15 meter  or  
> both.
> Rarely did
> I ever see a bad 80-40-20 meter  contact.
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R L MEASURES, AG6K. 805-386-3734

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