[Amps] SB-220's, 3-500's, some history

Fri Feb 6 15:44:49 EST 2009

The band switch of the SB-220 looks to me as one of a 100W transmitter from
the 60s.

73
Peter

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of gudguyham at aol.com
Sent: Freitag, 6. Februar 2009 20:51
To: km1h at jeremy.mv.com; amps at contesting.com
Subject: Re: [Amps] SB-220's, 3-500's, some history

Carl et al, not an adervetisment by any means.? What prompted this writing
was the awareness of the insane prices that are being paid for Sb-220 amps
particularly on EBAY for these amps that many can't say even work.? I have
heard horror stories about those paying high prices for even dead amps.? I
just wanted to enlighten the newbies who I feel are the ones pumping up the
price on them and don't know the pitfalls.? There "should" be more
accountablity by the sellers of some of this junk, but you will notice that
most every amp on EBAY comes with a disclaimer and a "all sales final"
slogan.? There was a time when a ham's "word" meant something, but not
anymore.? EBAY is a dumping grounds.? So I figured if buyers knew the
pitfalls etc, they might? be able to put the pressure on the sellers to
assure them that "at least" you might be getting an amp with a good
bandswitch.? When you consider the odds that you agreed with me on, there is
good chance one will get a bummer amp.? Th  ey can look clean as a whistle
trust me, but that band switch could be toast.? Fortunately for US Carl it
doesn't matter too much.? I have had better luck on the other buying venues
where seller responsiblity is at a higher standard, but I have STILL been
burned there too.? I haven't seen as many Drake L4 amps, but I assure you I
have seen more than most, and I have never seen a bad band switch on an L4,
L4B.? For use an an HF amp, I would take an L4B over an Sb-220 any day
especially in the used market.? You can almost bet the band switch will be
good on one of them, but I would not bet the same on the Sb-220.?
Please....DON'T ask me why the band switch contacts go south, the pit bulls
have argued this point for decades, need I say more?? Suffice to say these
are the facts regardless of the causes.? Lou

-----Original Message-----
From: Carl <km1h at jeremy.mv.com>
To: Gudguyham at aol.com; amps at contesting.com
Sent: Fri, 6 Feb 2009 1:09 pm
Subject: Re: [Amps] SB-220's, 3-500's, some history

Nice advertisement Lou, business must be slow down there <G>?
?
However with over 250 SB-220 family 6M conversions and many straight repairs
since the 60's I concur with 99% of the observations.?
?
All the Amperex are graphite and I have a NIB pair of the Eimac graphites in
my tube collection as well as a pair of Russian prototype 3-600Z's there
were never released to market.....they didnt work very well.?
?
Meanwhile, back to work, finishing up a LK-800A 6M conversion.?
?
Stay warm, I see global warming has frozen another elderly homeowner.?
?
Carl?
KM1H?
?
----- Original Message ----- From: <Gudguyham at aol.com>?
To: <amps at contesting.com>?
Sent: Friday, February 06, 2009 8:33 AM?
Subject: [Amps] SB-220's, 3-500's, some history?
?
> Unlike many hams who could count on one hand how many SB-220 amps they >
have?
> owned in a life time, some have to go to their feet to keep score. > Well,
I?
> am now starting to count hairs on my head and thankfully I have not >
experienced?
> Alopecia quite yet. All kidding aside, I have had HUNDREDS of Sb-220 >
amps?
> though here on my bench in the last 12 years. I have also seen all > the
sets?
> of 3-500 tubes that were in them as well. Beginning with the SB-220,?
> statistically the average used SB-220 has at least one burned or >
vaporized band?
> switch contact!! I would venture to say that 7 out of every 10 amps I >
have seen?
> have a bad contact. That is pretty bad odds. If you are looking to > buy
an?
> SB-220 you should be real concerned about this!! Often times if the >
contact?
> is not vaporized that amp still works because the contacts are >
redundant.?
> Sometimes only one contact on one side is bad and on the other side > it
is "OK".?
> As soon as a high SWR is present or some mistuning, you'll here an > arc
come?
> from that contact. In the long run, if you use that band a lot, > failure
is?
> close by. Those are pretty bad odds. The problem is it is very hard > to
see?
> the contacts on the switch and the inside contact is almost > impossible?
> without the use of a bright light and a dental type mirror. Most > other
problems?
> are simple to fix, but this problem is a bummer. Keep this in mind. > OK,
now?
> for the 3-500's. The Sb-220 has been around for a long time, most of >
them?
> made around the time when we all used "load em up radio transmitters" >
most of?
> them were capable of over 100 watts output, some Drake and Swan radios >
put?
> out 250 watts. Even the lower wattage radios did 160 to 180 watts >
output.?
> You could kill a pair of 3-500's with this kind of power input > levels.
SO I?
> have seen my share of weak tubes. As time went on and the usual > solid
state?
> 100 watt radio was the norm, you would be hard pressed to destroy a > pair
of?
> 3-500's with only 100 watts drive in an SB-220. So the odds of > getting a
full?
> output set of tubes in an Sb-220 is very high. I'd say in the 90 >
percentile!!?
> Well that's some good news. I have also seen many different types > of?
> 3-500s. Eimacs, Amperex, and others, including the Chinese > varieties.
Eimac in?
> the early and late 60's made a run of graphite tubes, they looked >
different?
> inside, much like a Pagoda instead of the typical turbine fan blade. >
Amperex?
> tubes all looked like this. Not sure if all were graphite or not, >
however I?
> have noticed in a small population of older tubes of this sort a >
difference?
> in bias requirements. Typically the standard 3-500 is self biased at >
about?
> 2500 volts or less and no additional bias voltage is required to > lower
the?
> idle current to about the normal 180 to 200 mills. The Drake L4.L4B > had
no?
> additional bias voltage. The SB-220 with about 2900 volts on the > plates
has?
> about 5 volts of bias which settles the tubes down to about 180 mills. >
If you?
> run the tubes beyond 3000 volts you will need 5+ volts of bias and as >
high as?
> 13v as in the Ameritron AL-82. Interestingly however, there was > "some"
and I?
> have only seen very few old Eimac and Amperex 3-500 tubes that seem > to
be?
> self biased at 3000 volts and require no additional bias to lower the >
idle?
> current to 180 to 200 mills. At first when I encounter these tubes, I >
thought?
> they were bad since the idle current when biased at 5 volts is so low, >
but in?
> the long run they are full output. I've used several Chinese brand > tubes
in?
> the past and I have always been pleased with them. Their performance > is
right?
> up there with the top brands. The Sb-220 itself had some evolution, >
there?
> were 2 different types of loading variable caps used, the Sb-221 used > a
wider?
> spaced tune cap. The Sb-221 did not have 10 meters unless it was > built
like?
> anSB-220 in the beginning by the builder buying the "10 meter kit". > The?
> Sb-221 as it is lacks a 10 meter contact on the band switch so it is > no
simple?
> "mod" to make one work on 10 meters. You'll need an extra contact on > the
input?
> switch as well and some input coils. They did due diligence on > keeping
the?
> CB'ers from using this amp easily!! Ditto for the later HL-2200 amp. > It
has?
> been a rewarding experience for me to have done these hundreds of >
autopsy's.?
> I am getting to fell like the Dr. G. of Sb-220's. My morgue is ever?
> expanding. 73 Lou W1QJ?
> **************Stay up to date on the latest news - from sports scores >
to?
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