I can appreciate the fact that some hams just do not have the money for an
Alpha or Acom. Rather than buying Ameritron junk why not buy a used Drake
L4B or a Tentec amp, or even an SB220/200. Even the lowly Heathkit amp was
built with higher quality parts and sound design. It makes me sick to see
all the hams around the MFJ booth at Dayton. I would never allow an MFJ
product in my shack. I guess I'm a throw back to an earlier age of ham
radio.
Bob
----- Original Message -----
From: "Will Matney" <craxd1@verizon.net>
To: <amps@contesting.com>
Sent: Friday, September 30, 2005 8:00 PM
Subject: Re: [Amps] Ameritron AL-811H-- Again
> Bob,
>
> I gotta say, the writer of that letter sounded like he was surely mad
> about something. When an amp is built cheap, it's cheap and no matter how
> much paint and flashing lights you add to the outside, it's still cheap on
> the inside. It sounded to me the designer pretty much admitted to it.
> However, there's some folks that don't have the money for an Alpha on the
> other hand and get by fine using the 811, etc. What I noticed though is
> the author never mentioned the internal layout of the amp as that has as
> much to do with an amp as every part in it. Long lead lengths cause stray
> capacitances which can lead to strange behavoir I'll call it. It's funny
> too that they'll argue there's no such thing as this problem but still use
> supressors to stop it. That's a big can of worms I don't want to reopen
> here as it's been quiet for a looooong time. Some amps are more prone to
> this behavior too not only because of layout but because of the type of
> tube used. These tubes have high gain and h
> igh interelectrode capacitances. Eimac is fully aware of this and have
> wrote numerous times about it in their literature and letters to some
> hams. I think I'll stop there and let others comment more as that's about
> all I know to say.
>
> Best,
>
> Will
>
>
> *********** REPLY SEPARATOR ***********
>
> On 9/30/05 at 7:32 PM Bob Maser wrote:
>
>>Bottom line, Ameritron is junk. Its big plus is that they are cheap.
>>Aren't they owned by MFJ?
>>
>>Bob W6TR
>>----- Original Message -----
>>From: "Jim Reid" <reidj021@hawaii.rr.com>
>>To: <amps@contesting.com>
>>Sent: Friday, September 30, 2005 5:33 PM
>>Subject: Re: [Amps] Ameritron AL-811H-- Again
>>
>>
>>> Here is the reply I rcv'd this morning from Tom Raush, W8JI,
>>> who designed the AL-811H for Ameritron.
>>>
>>> Some personal stuff at the opening, is deleted, and he did give
>>> permision for me to pass this info along to those of interest::
>>>
>>> "Hi Jim,
>>>
>>> ...snip...
>>>
>>> 1.) The common failure in 811 and 572 amps is tubes. The
>>> common mode of failure is high vaccuum or gas arcs. Although
>>> most likely under periods of high peak anode voltage
>>> (operation), flashovers can occur under ANY condition when
>>> HV is present. Sometimes the arc itself breaks down the gas
>>> and getters the tube, sometimes a tube is not recoverable.
>>>
>>> 2.) The resistor in the grid are to improve balance between
>>> tubes. The capacitors keep the grid at chassis potential for
>>> RF, and this is to SHIELD the cathode from the anode. The
>>> grid is the ONLY isolation for feedthrough capacitance. The
>>> values were chosen to minimize unwanted coupling through the
>>> tube and to equalize the drive to tubes over a normal range
>>> of replacement tubes. I wouldn't let a backyard mechanic
>>> without a network analyzer suggest new values based on
>>> emotional opinion.
>>>
>>> 3.) You can add as much nichrome as you like and you will
>>> have the same tube problems. The problem is not parasitics.
>>> The original suppressors are perfectly [adequate]..
>>>
>>> 4.) The meters are already protected. 100% of [such] meter
>>> failures are caused by the negative rail of the
>>> electrolytics rising above ground when the HV dumps to
>>> chassis ground through the tube anode to grid flashover. The
>>> current flows back through the grid shunt to the negative
>>> rail, and that is what blows out the grid shunts and meters.
>>> If anyone took the time to trace the current path they would
>>> see a single negative rail clamp diode protects the metering
>>> system.
>>>
>>> 5.) The "bang" occurs because things outside the tubes move
>>> and arc when you dump over a thousand volts to ground
>>> through five or ten ohms of power supply ESR. If you double
>>> that resistance by adding a 10 ohm series resistor, you
>>> reduce the surge current to half the value. It will still
>>> damage things. 75 amps of HV current isn't much better than
>>> the 150 amperes. If you really want to do glitch current
>>> suppression you should add at least 25 ohms using a HV surge
>>> rated resistor.
>>>
>>> Anyone is welcome to do whatever they want, but the fact is
>>> if the tubes are good there isn't a problem. If one or more
>>> is bad you'll have a problem even with dozens of circuit
>>> mods. If you have problems with an 811 or 572 amp it will
>>> almost always just be a tube or tubes. That's because tubes
>>> are cheaply manufactured and inadequately tested and
>>> conditioned before being sold. 3-500Z's are getting that way
>>> also.
>>>
>>> Tubes are costly to build correctly, that's why Eimac dumped
>>> glass tubes years ago, and why the people who bought the
>>> glass tube line weren't sucessful. We have to live with what
>>> is being manufactured and sold.
>>>
>>> For example, the Chinese manufacturers I've seen don't even
>>> highpot the tubes for voltage breakdown. In the mid 1990's
>>> they were testing production 572B's at 200 watts output with
>>> 1700 volts on the anode!! This is fodder for people with an
>>> agenda because it means there will be significant numbers of
>>> field failures related to flashovers.
>>>
>>> If you want to increase tube life in the 811 series, plug in
>>> 572B's. They are tested about like they should be testing
>>> 811A tubes. They have high reserve dissipation, so you are
>>> not likely to "cook" the anodes by overdissipation. The
>>> stated intention when designing the 811 amp was to build a
>>> very cheap amplifier. The cheapest amplifier possible for a
>>> given output power.
>>>
>>> There could have been $100 dollars of additional circuitry
>>> like a 25 ohm 25 watt HV fault resistor, a series 50 ohm 50
>>> watt cathode feedback resistor, and even a bigger tank coil
>>> and more expensive meters. Even with all that the tubes
>>> would by far remain the weakest link in the system. There is
>>> little point in installing rear wings on the back of Hondas
>>> with weak 4 cylinder engines that go 100 mph maximum, but
>>> some people want to do it. Myself, I prefer to get the BIG
>>> problems first. Change the tubes. Chinese 572B's are about
>>> as good as old RCA 811A's were at the same power.
>>>
>>> 73 Tom"
>>>
>>> Very interesting information.
>>>
>>> 73, Jim W6KPI/KH6
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
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