[1000mp] HEATHKIT SB-200 vs YAESU MUSEN FL-2100B

[Mike Schatzberg]

Hello Tom and Yaesu Fans....

You folks at Heath most certainly built what has become an Amateur Radio
Classic, in the SB-200...rugged, reliable, stable, and most of all, the best
performance per dollar available....I built mine, more or less around 1968,
and have logged thousands of on the air hours...I have only changed my
Cetron 572B's once, in all these years, and that was preventive
maintenance...naturally, I always minimize the grid current, by advancing
the loading as much as possible, while tuning for maximum power output, and
never exceeding 500 mils keyed down current on the grids...This will often
result in slightly more than 500 mils plate current, key down, and around
750 watts pep output, with adequate high voltage...perhaps 2400 volts while
idling in standby, and a stiff 230-240 AC volt line supply...I used a variac
to maintain the 2400 volts...While driving the amp in SSB, the grid current
will show less than 250 mils on voice peaks, on the SB-200's meter...While
the tubes run hot, I have never experienced a failure in 30 plus years of
operation, and two tone testing has always shown linear output...I can not
offer any comments on any other tubes other than the Cetrons...I bought 4
pair of spares directly from Cetron in 1969, for $17.50 each, and still have
6 unopened boxes today...

Regarding your comments on the bigger brother, which offers about 3 db
improvement in output over the SB-200,  you may recall from previous
communications, that my SB-220 has Chinese Pride tubes, which had operated
with great instability and lack of efficiency...and yes, your postulation
that poor vacuum may indeed be the culprit here, is certainly a reasonable
explanation...once the tube is sealed however, how does one determine
whether it's vacuum was pulled down sufficiently?....Until I try several
other Chinese tubes,  for which I am now waiting to arrive, I will not
really have a complete picture of what occurred...I only can say for now,
that after the changes were completed, all my issues disappeared
suddenly...and the amplifier operates with both efficiency and
stability...This may be due to the "gettering" of all remaining atmosphere
within the envelope, the circuit modifications, or a combination of both...

I still say, the SB-200 is a classic, go for it and enjoy.....

73,

Mike Schatzberg
WB2AJI
http://www.qsl.net/vu2wap/wb2aji/


----- Original Message -----
From: "Tom Rauch" <w8ji@akorn.net>
To: <1000mp@mailman.qth.net>
Sent: Sunday, February 17, 2002 2:01 AM
Subject: Re: [1000mp] HEATHKIT SB-200 vs YAESU MUSEN FL-2100B


> > I have both the SB 200 and SB 220 here, and they both work well with
> > my Mark V...Do not exceed about 500 mils grid drive on the SB 200, and
>
> Ouch! That is far far too much grid current!
>
> The grid current should be 100mA or less on a pair of 572's, and
> 250mA or less on the 3-500Z's.
>
> having more grid current than that is a sign of light loading, which is
> by far the largest cause of arcs in tank components.
>
> > within mine...and it is stock...I can not say the same for the SB 220
> > with a pair of high mu Chinese 3-500ZG tubes...I will publish an
> > article about my experience with these higher gain tubes, in the
> > original circuit...and what it takes to calm it down..
>
> The reason you probably though you had high gain and instability
> is the Chinese 3-500Z tubes are not pumped down well.
>
> I see hundreds and hundreds of tubes, and virtually 100% of the
> Chinese tubes have internal voltage breakdown problems because
> they lack a full vacuum. They also have poor metal-to-glass seals,
> and tend to have an abnormal amount of "leakers".
>
> The slightest amount of gas in a tube greatly reduces voltage
> breakdown. A typical Eimac 3-500Z used to hold off nearly 15kV of
> dc potential, while most Chinese tubes I've seen were lucky to hold
> off six to eight kV.
>
> Since peak anode voltage reaches nearly twice the dc anode
> voltage, the tubes live right on the edge of failure. If you underload
> or overdrive the PA, the peak anode voltage can climb much higher.
>
> The result is an arc or a "big bang" often wrongly attributed to a
> "parasitic".
>
> Russian 572B's were similar, they failed at about 5-6kV.
>
> I'm working now with a Chinese manufacturer of 572B's, and they
> are testing the 572's at 1600 volts and at 120 watts output!
> Approximately 90% of the tubes fail the same testing a Cetron tube
> passes. Put them in your FL2100, and "bang"!
>
> The problem is not the "gain", but rather the lack of proper
> manufacturing and testing at the source.
> 73, Tom W8JI
> W8JI@contesting.com
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