Hello,
Yesterday at a local Hamfest I purchased my first HF amplifier (a
Heathkit SB-230). I understand that the tubes for these amps is very hard
to find and very expensive when you do find one (hmmm....perhaps one day
sell this off for parts...the tube alone equals most of what I payed for the
amp). Anyway, given these facts I am planning on babying this amp during
the tuning process. I have used a club amp many years ago, so am familiar
with tuning by dipping the plate, adjust load for output, repeat, etc. I am
also planning on purchasing Ameritron's inrush current protector to limit
wear on the amp. The final piece of hardware is a tuning pulser...Amertron
has one...the ATP-102...seems a bit pricey given what it does. I already
have an electronic keyer....could the same results be had by sending a
string of dits at around 50 or 60WPM or is the pulser a better way to go.
Also, any other tips on tuning and operating this amp? (I've read about the
limited parasitic protection and am debating adding a kit to improve that or
maybe just putting on new ferrite beads, but am going to take my chances for
now before going that route. I need to test this amp out soon before I
seller "forgets" my purchase (he gave me his call and contact number and
promised a refund if I had any problems with the amp).

Thanks a bunch!
Craig KB8FGC

Hi, Craig

If you do a Google search for Heath SB-230, you will see
a thread in the "AMPS" email reflector.

Here is a synopsis of the thread:

Tom Rauch W8JI reported that he once studied the SB-230
as a contract engr for Heath.

He said that the grid can be easily damaged since there is no
grid protection circuit at all. Load the amp heavily
(pi network loading capacitor adjustment) to keep
the grid current down, as a percentage of plate current.

The grid dissipation rating of an 8873
is only about 5W, (60 mA grid current in the SB-230),
therefore can be easily damaged.

Carl KM1H said the max plate
disapation rating is only about 200W using the heat sink
without a fan. A fan should be added.

Tom also said that a series 25 Ohm 25W
resistor should be added to the B+ supply (to protect
the tube in case of an internal arc).
Carl said to use an enameled wirewound for this,
not a cement resistor.

Richard Measures said that the stock SB-230 has plate
resonances near 150 MHz and a higher freq resonance
which can cause "Big Bang" parasitics.


In answer to your question,
a c.w. keyer should work equivalently to a tuning pulser
if you can reduce the "on" time of the dot keying
well below 50%, and smoothly control the power output
of your exciter in c.w. mode. Monitor the peak rf output
with a scope. The duty cyle of the ATP-102
tuning pulser can be reduced to about 10 percent.

73,
Ed Knobloch


Craig wrote:
Hello,
Yesterday at a local Hamfest I purchased my first HF amplifier (a
Heathkit SB-230). I understand that the tubes for these amps is very hard
to find and very expensive when you do find one (hmmm....perhaps one day
sell this off for parts...the tube alone equals most of what I payed for the
amp). Anyway, given these facts I am planning on babying this amp during
the tuning process. I have used a club amp many years ago, so am familiar
with tuning by dipping the plate, adjust load for output, repeat, etc. I am
also planning on purchasing Ameritron's inrush current protector to limit
wear on the amp. The final piece of hardware is a tuning pulser...Amertron
has one...the ATP-102...seems a bit pricey given what it does. I already
have an electronic keyer....could the same results be had by sending a
string of dits at around 50 or 60WPM or is the pulser a better way to go.
Also, any other tips on tuning and operating this amp? (I've read about the
limited parasitic protection and am debating adding a kit to improve that or
maybe just putting on new ferrite beads, but am going to take my chances for
now before going that route. I need to test this amp out soon before I
seller "forgets" my purchase (he gave me his call and contact number and
promised a refund if I had any problems with the amp).

Thanks a bunch!
Craig KB8FGC

See below....

On Sun, 18 Jun 2006, Craig wrote:

Hello,
Yesterday at a local Hamfest I purchased my first HF amplifier (a
Heathkit SB-230).

I had an SB-230 once and as a "half-gallon" DC input amp without any fan
but with a small size, it worked well. Once I was off resonance and the
thermal cut-out shut down the amp (would not activate the change over
relay) until the heat sink cooled off (another issue you may want to be
concerned in case it works or does not work).

Probably the issue that is more important than anything else is that the
8873 is conduction-cooled through a beryllium "thermal link" (one inch
by one inch by 1/4 inch, roughly in size, and beryllium
has the novel physical property that it is one of the few materials
that conducts heat but does not conduct electricity) and that beryllium
metal is chemically toxic to life. Recommendations for handling beryllium
includes that you do not touch it with your fingers, and you do absolutely
no machining on it including drilling, filing, cutting, etc. The dust
particles are even more toxic. If you go back through old QSTs or old
Heathkit catalogs and pay attention to when the SB-230 was discontinued,
then look in the QSTs for that date era, you will find a small
announcement about the fact the Heath decided to discontinue the SB-230
because of the toxicity of that thermal link (I remember reading it
myself). You can also get more recent copies of "The Handbook of Physics
and Chemistry" where you will also find a disclosure about the toxicity of
beryllium (you might just google the element and see if this fact shows
up).

I am sure that our enviroment includes all manner and well scattered
pieces of toxic, dangerous solids, liquids, etc., just waiting for us to
partake and get sick (read any history of Love Canal, etc., or any other
serious chemical spills where people were hurt), but you might want to
consider what you will do with that amplifier, someday, in the future. It
does not lend itself very well to modification to some other tube (I
thought about it myself). Long ago I sold my copy of the SB-230 to someone
and I don't remember if it was before or after I learned about the
toxicity of the thermal link, but I remember reading the very small notice
in QST from Heath about the problem and that that was the reason for
discontinuing the amp. There are water-cooled amplifier tube circuits
that, IIRC, don't need these beryllium thermal links and you might want
to look around at these for ideas.

Yes, all those 887X metal-glass/ceramic tubes went up greatly in price
over the years that they were being produced. Makes amps with 3-500Zs,
811s, 572-Bs look real good if you need to replace a tube or two or more.

Outside of that, I never had any problem with my SB-230 and I used it a
moderate amount when I had it.

I understand that the tubes for these amps is very hard
to find and very expensive when you do find one (hmmm....perhaps one day
sell this off for parts...the tube alone equals most of what I payed for the
amp). Anyway, given these facts I am planning on babying this amp during
the tuning process. I have used a club amp many years ago, so am familiar
with tuning by dipping the plate, adjust load for output, repeat, etc. I am
also planning on purchasing Ameritron's inrush current protector to limit
wear on the amp. The final piece of hardware is a tuning pulser...Amertron
has one...the ATP-102...seems a bit pricey given what it does. I already
have an electronic keyer....could the same results be had by sending a
string of dits at around 50 or 60WPM or is the pulser a better way to go.
Also, any other tips on tuning and operating this amp? (I've read about the
limited parasitic protection and am debating adding a kit to improve that or
maybe just putting on new ferrite beads, but am going to take my chances for
now before going that route. I need to test this amp out soon before I
seller "forgets" my purchase (he gave me his call and contact number and
promised a refund if I had any problems with the amp).

Thanks a bunch!
Craig KB8FGC