[AMPS] Re: [BitBucket] Ameritron/MFJ Reflector

[Tom Rauch (W8JI)]

Bill Turner wrote:
> --------------------------------------------------
> Ok, you've hit my hot button.  I have an Ameritron AL-1200 which I
> would rate as a fair piece of gear, but with some caveats:
> 
> 1.  When I received it, the safety interlock switch on the top cover
> was miswired.  With the cover off and power applied, the HV supply
> should have generated zero volts.  Instead, it generated over 400
> volts DC!  Nowhere near the full voltage of course, but lethal none
> the less.  The problem was in the way the transformer primary was
> wired.  The schematic in the manual was correct, so when I re-wired it
> to conform with the schematic, the interlock worked fine.  I sent this
> information to Ameritron with before and after schematics, but never
> heard a word back from them.  Some things are too painful to
> acknowledge, apparently.

Not actually. Your letter resulted in correcting of a wiring jig, and
that problem was corrected. It was caused by the step-start relay coil
shunting the path for the supply interlock. You are correct, it produced
200-500 volts when the cover was removed.

Everyone should remember, and PAY ATTENTION to warning labels and
instructions. Never plug the amplifier in with the cover removed. There
is at least 240 vac available if you do, plus you bet you life there are
no component or wiring errors.

> 2.  The slow-start circuit was very inadequate, in my opinion.  The
> amount of delay was way too short, only a few milliseconds.  As a
> result, when the delay relay closed, there was a humongous arc at the
> relay contacts.  I'm talking an arc hot enough to light the room.  I
> removed that circuit and installed an Amperite time delay relay in
> it's place.  Now there's a nice slow, four-second warm-up and the amp
> comes on gentle as a kitten.  The previous design is inexcusable.

Mmm. The normal delay is a result of the primary reaching 80% of its
full voltage, and pulling in a relay. The function of the circuit is to
start the amplifier through a ten ohm resistor, limiting line inrush to
24 amperes until the primary current drops to about eight amperes. At
about 8 amperes the resistor is removed, leaving the next peak current
at 12 amperes.

If the re-wired relay was wired correctly, you saw the arc from either
the initial 24 ampere closure (which has nothing to do with delay time)
or the second arc of 12 amperes.

> 3.  After running some full-power RTTY on 160 meters, I smelled
> something funny.  Upon removing the cover, I noticed the last three or
> four turns of the 160 meter coil had melted the plastic rods which
> hold them.  That end of the coil is right next to the cabinet, so
> presumably there was some coupling to the (lossy) steel case. I
> removed the melted turns, figuring their loss would only increase the
> Q slightly and not really hurt anything.  It did tune up ok, but I
> never ran RTTY on 160 again.  Shortly afterwards, I sent email about
> this to the designer who said "Hmmmmm... most people don't run RTTY on
> 160 meters.  I'll look into it."  I never heard back from him either.

The cabinet had nothing to do with the problem, except as it blocks
airflow. The design was never RTTY rated and there are no specs, that's
why you get no answer from me. That design did output 1500 watts in
bench tests for 1/2 hour on all bands from 14 MHz on down, but users
need to understand that a bench test is far different than field
operation. 

The end user might tune the PA differently, have different ambient
temperatures, differnt supply voltages, production differences, etc. The
only way to get a complete idea of how reliable any PA is through field
service history.

Unfortunately, not that many people operate RTTY on 160, so data is
unreliable.    

But in normal CW and SSB contest operation (which was the target market)
the 1200 and that mainframe group are very reliable even after years of
service.

My answer to the RRTY question on 160 remains "I don't know". Sorry.

> 4.  During the last RTTY contest, I had been running stations on 80
> for about an hour when there was another room-lighting arc and the
> power output dropped to zero.  To make a long story short, the 80
> meter tank coil had gotten hot enough to melt the solder attaching the
> tap, and it let go.  In additon, the whole 80/160 meter coil supports
> had melted and the coil twisted itself into a replica of a slinky toy.
> In spite of it's "1500" watt rating, this amp can not do it on RTTY,
> at least on 80 or 160.  Better cooling in the output tank area is
> definitely called for.

This is a case I can address. I can assure you the amp is NOT RTTY
contest rated unless HV is reduced.
 
> 5.  When the amp was about nine months old, the 3CX1200A7 blew with no
> warning.  Calling CQ on 15 and all of a sudden, a loud bang and the
> lights went out.  Turned out the tube shorted from grid to anode.
> Luckily there was no other damage, and Ameritron replaced the tube
> under warranty with no problems.  This is no fault of Ameritron's of
> course, but it happened.

Service history on the 1200 tube is excellent, the number of warranty
failures are less than 1.8 percent of 8877 failures, and less than 23%
of 3-500 failures. That includes the time period in the 80's when Eimac
was having manufacturing problems with 8877's.

> So as you can see, the AL-1200 has it's problems.  I have used it hard
> for the last year and a half, and aside from the above, it's done the
> job just fine.  However, if I had to do it again, I wouldn't buy one.
> I'd either get an Alpha or build a battleship-style homebrew.  Since I
> don't care to spend what an Alpha costs, I am building an 8877
> homebrew which is about 80% done.  It will cost about half what the
> Ameritron did and should be about twice the amplifier.  You'll be
> hearing it by summer.

Cost is always an issue. Ameritron never did target the high end market,
because that isn't where the sales volume is. If there is any area of
the 1200 series (82/1200/1500)that needs work it is in the tank and
relay area. The tank needs vacuum capacitors to save space for larger
inductors and control Q on 18 MHz and up better.

The antenna relay could be replaced with a vacuum relay. 

Unfortunately when the PA was designed, the market dictated restricting
cost to satisfy SSB and CW operators who wanted a heavy duty amplifier.
The market would not tolerate another ETO high dollar design, caused by
the $1800 price increase the next step up would bring.

As a matter of fact Ameritron has had a prototype PA with three
3CPX800's, and another with two 8877's (and vacuum caps) for six years
now. They were never released because the cost was unreasonable.

By the way, I do design work for MFJ, Ameritron, and also other
companies (even some competing PA's). I only look at products on a "per
request basis", since I am now an outside contractor. I do forward all
correspondence to Martin Jue and his crew.

Gary was correct about the AL-1200 on display at Dayton last year. When
I saw the sloppy construction I raised hell with Martin Jue and his
crew. After a series of meetings and moving some people around, the QC
is back on track.

I appreciate critical comments, because it keeps me in the loop. Honest
first-hand comments like Bill's and Gary's are constructive. It's the
blather and second hand rumor some people persist in that I dislike.

73, Tom


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