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
warrant?
>
> 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: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Gudguyham@aol.com
> Sent: Saturday, June 03, 2006 10:42 AM
> To: r@somis.org; n4zr@contesting.com
> Cc: craxd1@verizon.net; amps@contesting.com
> Subject: Re: [Amps] R. MEASURES PRAYERS ANSWERED
>
> In a message dated 6/2/2006 5:47:24 PM Eastern Daylight Time,
> r@somis.org
> 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
r@somis.org
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