Hi Cliff , I just got a bird 8141 dummy load from bird and it is rated at
250 watts continuous that should translate to well over 1.5 KW for short
periods of time . Thiswas told to me by a dealer in these surplus dummy
loads. check with Max Gain systems in marietta GA. John
----- Original Message -----
From: <amps-request@contesting.com>
To: <amps@contesting.com>
Sent: Saturday, December 13, 2003 12:00 PM
Subject: Amps Digest, Vol 12, Issue 29
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> Today's Topics:
>
> 1. Big Solid State Amplifiers
> 2. Tetrode blue glow (John Nelson)
> 3. Re: 3-500Z plate durability
> 4. 3-500Z plate durability (Rob Atkinson, K5UJ)
> 5. MLA-2500 Relay too loud! (Don Knight)
> 6. Re: ELECTRICAL INSPECTIONS (R.Measures)
> 7. Re: 3-500Z plate durability (R.Measures)
> 8. Re: MLA-2500 question (=?iso-8859-1?q?Roger=20Parsons?=)
> 9. Bird 8230 Dummy Load (Cliff Bond)
>
>
> ----------------------------------------------------------------------
>
> Date: Fri, 12 Dec 2003 19:28:11 -0000
> From: gw4dgu@blaenffos.org
> To: <amps@contesting.com>
> Subject: [Amps] Big Solid State Amplifiers
> Message-ID: <002301c3c0e6$14ce95c0$6c01a8c0@network.blaenffos.org>
> References: <20031212170020.C239331A73C@dayton.akorn.net>
> Content-Type: text/plain; charset="iso-8859-1"
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>
> Since returning to active amateur radio after a break of nearly two
decades,
> I've been a bit saddened to see that many hams seem to be shying away from
> solid state amplifiers, and investing them with negative properties that
> they don't necessarily have.
>
> I think there are a couple of perceptions that need altering. Largely
these
> come about from the amateur insistence on running everything on 12V
> supplies. While that's fine for mobile kit, it does nothing for linearity
or
> efficiency! Even moving to 28V makes a huge difference to both parameters:
> 50V devices are even better!
>
> Another major problem is that hams tend to look at solid state devices as
> though they are just another form of vacuum tube. They're not. Solid-state
> devices have their own strengths and weaknesses, and from a systems
> viewpoint they need to be treated differently to tubes to get the best
> performance. Although it's possible to get quite decent power and
linearity
> from modern MOSFETS (big RF power bipolars are effectively obsolete) in an
> open-loop amplifier - my 600W (saturated) FET amplifier for 144MHz ,
> operating on 28V, does better than -30dB intermods up to about 530W pep -
> the real prize comes when you start to apply linearisation techniques,
most
> of which are difficult (but not impossible!) to achieve with tubes. We can
> use the low cost of complexity which solid-state brings to the game, to
> improve the performance of equipment. The guys designing MF AM broadcast
> transmitters using arrays of switch mode power amplifiers are commercially
> driven. Modern transmitters in this field offer much greater efficiency,
and
> thus lower running costs, than traditional tube designs. And I'd be
prepared
> to bet that the modulation linearity is better, too!
>
> I do most of my professional work on VHF-UHF transmitters, and I've
recently
> seen a demonstration of a linear UHF transmitter with the equivalent
> of -60dB third-order IMD rejection, and a final amplifier efficiency well
> into the high 70% region. The PA was running well into saturation while
> producing this level of performance.....
>
> If, as amateurs, we were to adopt techniques such as cartesian loop
feedback
> linearisation we could make much better ssb transmitters than are used
> currently. -60dB intermods and <60% PA efficiency could be relatively
easily
> achieved, perhaps even on 12V! This isn't pie in the sky stuff: the
> techniques are even employed in uhf digital handhelds (TETRA/APCO etc).
The
> major Japanese manufactures of ham equipment are well aware of the
> techniques, and the additional hardware component costs to add CFBL
> linearisation to a modern HF transciever would maybe be of the order of
> twenty euros/dollars.
>
> Perhaps a campaign for better transmitters could follow on that which led
to
> receiever performance improvements twenty years ago? One great advantage
of
> a properly designed linearised transmitter would be that it would be very
> difficult to overdrive.........!
>
> 73
>
> Chris
> GW4DGU
>
>
>
>
>
>
>
> ------------------------------
>
> Date: Fri, 12 Dec 2003 17:20:22 -0000
> From: "John Nelson" <john@steampower.demon.co.uk>
> To: <amps@contesting.com>
> Subject: [Amps] Tetrode blue glow
> Message-ID: <000c01c3c0d4$60089200$0100a8c0@tiresias>
> References: <20031212170021.67F0031A2AA@dayton.akorn.net>
> Content-Type: text/plain;
> charset="Windows-1252"
> MIME-Version: 1.0
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> Message: 2
>
> >erie blue light from the ceramic anode-screen insulator. <
>
> Next to the colour of an F-4's jetpipes with reheat selected, this is
surely
> the most beautiful blue in the world.
>
> 73 John
> GW4FRX
>
>
>
> ------------------------------
>
> Date: Fri, 12 Dec 2003 10:58:56 -0500 (EST)
> From: jsb@digistar.com
> To: "R. Measures" <r@somis.org>
> Cc: Joe Isabella <n3ji@yahoo.com>
> Cc: Amps <amps@contesting.com>
> Subject: Re: [Amps] 3-500Z plate durability
> Message-ID: <Pine.GSO.4.58.0312121045420.27486@digistar.com>
> In-Reply-To: <200312121325.hBCDPOwD022537@digistar.com>
> References: <200312121325.hBCDPOwD022537@digistar.com>
> Content-Type: TEXT/PLAIN; charset=US-ASCII
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> Message: 3
>
> On Fri, 12 Dec 2003, R. Measures wrote:
>
> > >I have to learn to be more careful though - i've been sloppy keeping
> > >the grid current under 260mA when tuning.
> > >
> > ** 3-500Zs have no grid-I rating. They have a grid-dissipation rating
> > of 20w -- which can be exceeded (as in glowing grid wires) for brief
> > periods without damage. Grounded-grid/cathode-driven amplifiers should
> > not be adjusted with the grid-I meter. Instead, they should be tuned
> > with max rated drive, preferably pulsed, and adjusted for max P-out with
> > the Tune and Load controls. With P-out peaked, grid-current will always
> > be ok because excessive grid-I will always rob electrons from the
> > output.
>
> I wonder why grid current is measured instead of dissipation - I would
> think dissipation and current measurements could be easily interchanged
> for display on a meter.
>
> > Also, because grid-I only flows when the anode is not very positive,
> > too little grid-I tells us that the anode-V is not swinging low enough
> > during the peak in cathode-emission.
>
> Interesting - I thought Ep dropped because of traditional voltage drop and
> because typical plate voltage supplies are not regulated to the degree
> that filament voltages are regulated - so plate voltage drop is a
> necessity? Or should I read the drop as an indicator of proper electron
> flow?
>
> > Naturally, when this is happening, P-out drops off. Thus, for a
> > cathode-driven amplifier, tune for P-max and relax.
>
> ... and be sure to stop applying additional drive when P-max is reached?
>
> My usual method for tuning is to apply drive, look for maximum output,
> continue increasing drive and tuning for max output until one of the smoke
> alarms goes off (meter shows max acceptable plate current and/or grid
> current).
>
> I have also been experimenting with touching up the load to lower grid
> current with the result of increasing power output. This seems to yield
> an additional 200-400 watts at best over 1000 tuned to peak output. I've
> mostly abandoned this practice for the most part because of the scant
> increase in signal strength by the receiving station (most of my operating
> is on CW), however it does seem to help on SSB - however I do not know if
> the additional 200-400 watts are comprised solely of of splatter with no
> beneficial yield to the receiving station on the intended frequency.
>
>
> thanks,
> jason
> ------------------------------
>
> Date: Fri, 12 Dec 2003 18:17:35 +0000
> From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
> To: amps@contesting.com
> Cc: k5uj@hotmail.com
> Subject: [Amps] 3-500Z plate durability
> Message-ID: <Law14-F16RJnl3Xemb2000071f3@hotmail.com>
> Content-Type: text/plain; format=flowed
> MIME-Version: 1.0
> Precedence: list
> Message: 4
>
> The Centurion has the 3-500 sockets in a cage (elevated platform) which I
> thought was a standard chassis setup for cooling. The muffin fan is
mounted
> vertically inside the cabinet perpendicular to the rear panel so it sucks
> air in from the left across the plate transformer, through a rf deck
shield
> opening, and exhausts the air across the Ip filter choke and tubes. It is
> big enough to rotate below the sockets and move air through the cage
around
> the pins. This seems to be okay for low duty cycle.
>
> I have been told that RCA once made a mw AM bc tx that ran 1 kw carrier
> using two 3-500s for carrier and two for modulator. This unit had a big
> blower that moved a lot of air over those tubes. The quiet muffin fan
would
> not have done the job.
>
> What Rich Measures said about tuneup of the gg cathode driven 3-500 amp is
> another reason for owning one. Tunup is a breeze.
>
> I run two into a near pure restance 50 ohm load +- 1 or 2 ohms and at 1 or
> 1.1 kw pep plates show no color at all. With less than optimal load I see
> some color. I have no sophisticated tank circuit load matching genius to
> explain this, that is you experts department--only observation. If you
are
> worried about long carrier transmission try tuning out all load reactance
> and getting near 50 ohms & maybe that will help. I know some wise guy
will
> say no one ever got a bad sig. rpt due to high swr but your amp and
feedline
> (the part to the transmatch) will be happier.
>
> Rob Atkinson
> K5UJ
>
> _________________________________________________________________
> Our best dial-up offer is back. Get MSN Dial-up Internet Service for 6
> months @ $9.95/month now! http://join.msn.com/?page=dept/dialup
>
> ------------------------------
>
> Date: Fri, 12 Dec 2003 12:11:39 -0500
> From: "Don Knight" <n4dek@triad.rr.com>
> To: <amps@contesting.com>
> Subject: [Amps] MLA-2500 Relay too loud!
> Message-ID: <005801c3c0d3$01ee4210$deae5818@yourxu5v9frokn>
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> charset="iso-8859-1"
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> Message: 5
>
> Is it possiable to change out the loud antenna relay in the MLA-2500? =
> This thing just makes way too much noise! Maybe a vacuum relay that =
> would be a simple replacement?
>
> Thanks,DonFrom
on5km@planetinternet.be Fri Dec 12 18:30:46 2003
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> Sat, 13 Dec 2003 00:30:42 +0100
> Message-ID: <001f01c3c107$f26a7220$14b50b51@computer>
> From: "Stefaan Van Laecken" <on5km@planetinternet.be>
> To: <amps@contesting.com>
> References: <mq1htv4ff3phh8pbolq4evrn1i8stbff0s@4ax.com>
> <200312121019.51500.g8gsq@qsl.net>
> Subject: Re: [Amps] Homebrew solid state amps?
> Date: Sat, 13 Dec 2003 00:30:36 +0100
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>
> if you want to give it a try , you could always look out for a surplus RF
> generator used in microelectronics manufacturing.
> most of them are tuned on 13.56mhz but can be modified without any
problems
> .
> some of them are using several moduls with a combiner . mine has a pair of
> MRF448 on a max power of 500Watts.
> But as they say : there are not lineair , there working in class C
> .........
> An other thing is that the blowers are making a hell of noice ........
>
> The new RFgenerators on the QRL are good for 1 Kwatt solid state , but the
> prices are VERRY high .
> So gess you have to wait a little to find a surplus gen.
>
> 73 ON5KM Stef
>
>
>
> ------------------------------
>
> Date: Fri, 12 Dec 2003 09:50:28 -0800
> From: R.Measures <r@somis.org>
> To: <Gudguyham@aol.com>, " AMPS" <amps@contesting.com>
> Subject: Re: [Amps] ELECTRICAL INSPECTIONS
> Message-ID: <20031212175148.AC46A31A7CF@dayton.akorn.net>
> Content-Type: text/plain; charset="US-ASCII"
> MIME-Version: 1.0
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>
>
>
> >The fact is REGARDLESS of who does the electrical work in a home the
> >building
> >inspector "most likely" will NEVER actually try to follow the wiring to
see
> >if one has overload a circuit with too many outlets. Of course an
> >overload is
> >determined by what is plugged in at any given time, but there are codes
on
> >how many devices can be on a circuit. Its nearly impossible for the
> >inspector
> >to pick up "wiring errors" of code. He will however pick you up if you
are
> >missing an outlet somewhere where code says there should be one, and
other
> >similar oversights. The code is a very funny thing and many times does
> >NOT make any
> >sense to a person who understands electricity (like most hams). For
> >example:
> > Its OK to run a 20A branch circuit and install up to 10 (ten) 15 amp
rated
> >outlets (the normal outlet we all have). But if you run a 20A circuit
> >dedicated for a washing machine or something and its the ONLY outlet on
the
> circuit,
> >then that outlet MUST be a 20A rated outlet. SO go figure. The code is
> loaded
> >with such things that really dont make sense, but these are the things
you
> >have to know.
>
> ** To me the tests that make the most sense require a simple DMM. They
> are.\:
>
> 1. check each outlet for the proper ground, neutral and line potentials.
> 2. measure the V-drop with a 15A electric heater load. [the V-drop
> should be under 4%]
> 3. plug a second 15A heater into the same outlet and see if the breaker
> trips before you smell smoke.
>
> >In MOST cases building inspectors are not electricians and most
> >inspectors have a routine on things they check. You can get the low down
on
> >any local building inspector and his "pet peeves" at the local watering
> >hole or coffee shop at about 4:30PM.....If you ever want to tangled up in
a
> web, try
> >wiring up a swimming pool.
>
> ** This is important because people around here have been electrocuted by
> a leaky underwater-light gasket in a swimming pool. If there is a best
> place for GFI circuit breakers, a pool has gotta be it.
>
> >Inspectors are all over the Universe with the
> >code on grounding of pools. ...
> ------------------------------
>
> Date: Fri, 12 Dec 2003 10:19:35 -0800
> From: R.Measures <r@somis.org>
> To: <jsb@digistar.com>
> Cc: Joe Isabella <n3ji@yahoo.com>
> Cc: Amps <amps@contesting.com>
> Subject: Re: [Amps] 3-500Z plate durability
> Message-ID: <20031212182054.F1FC031A035@dayton.akorn.net>
> Content-Type: text/plain; charset="US-ASCII"
> MIME-Version: 1.0
> Precedence: list
> Message: 7
>
>
>
> >On Fri, 12 Dec 2003, R. Measures wrote:
> >
> >> >I have to learn to be more careful though - i've been sloppy keeping
> >> >the grid current under 260mA when tuning.
> >> >
> >> ** 3-500Zs have no grid-I rating. They have a grid-dissipation rating
> >> of 20w -- which can be exceeded (as in glowing grid wires) for brief
> >> periods without damage. Grounded-grid/cathode-driven amplifiers should
> >> not be adjusted with the grid-I meter. Instead, they should be tuned
> >> with max rated drive, preferably pulsed, and adjusted for max P-out
with
> >> the Tune and Load controls. With P-out peaked, grid-current will
always
> >> be ok because excessive grid-I will always rob electrons from the
> >> output.
> >
> >I wonder why grid current is measured instead of dissipation -
>
> ** Grid-I is usually defined as average indicated current on a typical
> meter. A system for measuring actual dissipation would be considerably
> more complex. In any case, grid-dissipation is not a problem when an
> amplifier is tuned for max-P out instead of max grid-I.
>
> > I would
> >think dissipation and current measurements could be easily interchanged
> >for display on a meter.
>
> ** Hardly. Grid-I looks nothing like a sinewave because it only flows
> when the grid is positive, which is less than half of the driving cycle,
> and even then grid-I is not at all proportional to voltage.
> > ...
> ------------------------------
>
> Date: Fri, 12 Dec 2003 18:40:34 +0000 (GMT)
> From: =?iso-8859-1?q?Roger=20Parsons?= <ve3zi@yahoo.com>
> To: Amps <amps@contesting.com>
> Subject: Re: [Amps] MLA-2500 question
> Message-ID: <20031212184034.84413.qmail@web14919.mail.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
> MIME-Version: 1.0
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> Reply-To: ve3zi@rac.ca
> Message: 8
>
> Neither of my MLA2500s has a reflected power
> monitoring position - other versions may have. I think
> that the purpose of the trimmer is to try and make the
> flat across the frequency range. It fails
> miserably....
>
> 73 Roger
> VE3ZI
>
>
> ________________________________________________________________________
> Want to chat instantly with your online friends? Get the FREE Yahoo!
> Messenger http://mail.messenger.yahoo.co.uk
> ------------------------------
>
> Date: Fri, 12 Dec 2003 18:40:19 -0500
> From: "Cliff Bond" <WA4MWM@triad.rr.com>
> To: <amps@contesting.com>
> Subject: [Amps] Bird 8230 Dummy Load
> Message-ID: <01ee01c3c109$4dbcef80$6401a8c0@triad.rr.com>
> References: <004f01c3bf92$5d28ef00$9b9d3a41@colin>
> Content-Type: text/plain;
> charset="iso-8859-1"
> MIME-Version: 1.0
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> Message: 9
>
> Seasons greetings to all...
>
> I am in need of some info regarding the Bird 8230 dummy load.
>
> It is rated at 2.5kW continuous duty (with water flowing). Is it rated
for
> any intermittent-duty ratings? (i.e. For operation at power levels above
> 2.5 kW at less than continuous-duty?) If so, any reference to the
> intermittent-duty ratings would be most-appreciated.
>
> Thanks for the information,
>
> Cliff
> NC4CB
> Winston-Salem, NC
>
> ------------------------------
>
> _______________________________________________
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>
>
> End of Amps Digest, Vol 12, Issue 29
> ************************************
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