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