SB-220 parasitic suppressors.

[Steve Harrison]

At 12:23 AM 2/12/99 -0500, Multi-Volti Devices wrote:
[snip]
>The Rich Measures mod used a 3W Panasonic metal oxide resistor and nichrome
>wire, for lower Q.
......
>I strongly recommended the AG6K/Rich Measures/QST parasitic suppressor to
>customers who called or wrote to Heath Techical Consulting when I was there,
>especially for the SB-1000. I personally would leave them there if they are
>the metal oxide/nichrome suppressors, because I believe they are more
>effective.

They certainly are. While it is a little bit more difficult to solder the
nichrome wire, all the extra effort more than pays off in greatly-increased
stability using *any* variety of 3-500Z, under almost *any* operating
conditions (except, of course, no antenna!!).

..............
>I asked the question, "What is original spec?". According to Rich Measures'
>research, Eimac reduced mu many years ago from 200 to 160.
>
>If I remember accurately, he stated this was in response to amplifier
>engineers' inquiries about tendencies toward parasitic oscillation. Just
>because an amp has the grounded grid topology, it's no guarantee of
>stability.
>
>When I worked at Heath, we saw an incredible number of SB-1000's vaporize
>numerous components for no apparent reason (bandswitch contacts, bias zener
>diodes, meter movements). According to Rich Measures, he met with great
>resistance from one other amplifier company about his statement that the
>parasitic suppressors 'traditionally used' were ineffective. This particular
>company insisted the failures were from hot switching or operation
>(basically that customers were stupid). Rich's collection of published
>photos revealed there is definitely some common factor causing a problem.
>Not every ham with a 'linear' is an idiot (although some people listening to
>75 or 20 phone might disagree! :o)  ).

Measures published several articles in QST some years ago completely
describing these amplifier problems (which were not limited to Heath;
almost *all* HF amplifier models have, at one time or another, exhibited
one or more of these same catastrophic failure characteristics,
*particularly*, but not limited to, those using Eimac 3-500Zs or 8877s).
But within several years of publication, the ARRL printed still another
article which was actually a set of "interviews" with several so-called
amplifier "experts", one of whom was the the chief engineer of the company
mentioned above. All three of these so-called "experts" attempted to prove,
through innuendo and, where necessary, plain-skipping-around-the-facts,
that Measures was wrong and that there really *is no such phenomena as a
VHF parasitic oscillation*. The ARRL then declined to give Measures the
opportunity to publish a rebuttal, reply or response to the "experts".

Much later, a reflector known as the AMPS reflector came into being on the
internet. Almost immediately, Measures, the chief engineer of the company
mentioned above, and several other "experts" became embroiled in a long,
protracted discussion about this "VHF parasitic" phenomenon. The issue has
never been completely resolved to the point where either side can, with
100% certainty, claim they are correct.

Meanwhile, Measures parasitic suppressor kits continue to be added to HF
amplifiers using all kinds of tubes all over the world. And in virtually
every case, the amplifiers exhibit much more civilized behavior. The
"experts" on the other side of the fence continue to hem and haw around,
claiming other things have resulted in the increased stability.

But the amplifier owners who assemble and install the kits are the final
word; and very few of those folks will dispute the fact that their machines
now work much more reliably. The new suppresors, due to their design, *do*
result in slightly less output power on 10 meters in particular (I think
about 25 to 50 watts or so); but this is relatively insignificant when you
are talking about 1000 watts. And too, the 3-watt resistors in the kit
*will* operate *red-hot*! But, Measures specifically chose those resistors
for the ability to operate at such high temperatures, and also for their
lack of resonances below 100 MHz.

>....there was nothing wrong with the
>Chinese tubes, if they arrived working, anyway. They just had higher gain.
>He did point out that there were three mfg. plants (I can't remember who in
>China was making them, but a name like Sino keeps popping into my head).
>Some of the tubes could be seen visually to be defective, with badly
>misaligned anode structures, etc.

These quality and reliability problems have supposedly been cured (but I
have no personal experience or specific knowledge).

..............
>I got permission to try a Measure's parasitic suppressor kit in service and
>begin suggesting them to customers.......we found the Measures' parasitic
>suppressor in a non-statistical (due to circumstances) way produced
observable >improvement.
>
>I don't think the risk of damaging costly, or nearly unavailable, parts is
>worth the desire to have an original component that appears to be implicated
>in the problem.

The Measures parasitic suppressor kits cost something less than $20 for two
tubes, if I recall. And he provides telephone support if needed.

>The availability of alternate tubes and the alleged change of mu by Eimac
>seem to explain why the problem wasn't common for many years.

My company bought a brand new Henry 2K-Classic X for some HF radar
experiments about in 1991; the tubes were Eimac. For our special tests, we
needed to run the amplifier key-down for at least 30 minutes at 1200 watts
output on 27.990 MHz (under a special military license). At the lab during
the "familiarization" tests, the amplifier ran for over two hours with no
problem, straight from the box. In the field, it ran through a one-hour
prelaunch test the first day, then ran about 30 minutes the second day
before something went BANG!! and the HVPS diodes got killed; there was no
visible damage anywhere. Henry overnight-FEDEXed new diodes and we ran the
amplifier the next day about 10 minutes before the same thing happened
still again. I was standing there peering inside when it blew that day and
saw nothing at all until the main circuit breaker popped open. We replaced
the diodes again for the launch on the following day. The launch took
place, and THEN we turned on the 27 MHz rig. According to the PhD who was
manning the transmitter shelter for the launch, the amplifier lasted maybe
five seconds longer than the rocket did (the rocket went off-course and was
blown up about 15 seconds after launch), then the amp blew with the by-now
familiar BANG!!!. Every time the amp blew, it sounded like a shotgun went
off in the transmitter shelter.

Several months later at home, after replacing the blown bias zener diode
and meter, I installed the Measures suppressor kit, then with great
trepidation and fingers stuck solidly in my ears, fired up the amp again.
An hour later, I finally shut it down, still putting out the original 1200
watts, with no BANG!!!. And using the original tubes. I was able to borrow
the amp for home use during the next year and ran the living heck outta it
on all bands, 80 through 10 meters, CW, during a pair of 48-hour DX
contests. It never blew up again.

So, what am I to conclude? You tell me!

>Thanks for the BW, as people say (I usually don't, I just ramble).
>
>Murray

Me, too, Murray! And no, I have no connection with Measures whatsoever.
Haven't even spoken with him since buying the suppressor kit over five
years ago.

73, Steve Ko0U/1

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