[Amps] Ameritron AL-811H-- Again

Fri Sep 30 20:17:54 EDT 2005

Bob,

Gimme a Drake L4-B any day and I'm satisfied. The SB-220 is a good choice but you may have to re-work bad construction techniques as you never know who built it. Same as the rest of the Heath products. There was an old Swan amp that used 811's in it I can't remember the model though that was all right. But yes, there's a bunch of used amps out there that are top of the line and one can now afford them.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 9/30/05 at 8:11 PM Bob Maser wrote:

>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 at verizon.net>
>To: <amps at 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 at hawaii.rr.com>
>>>To: <amps at 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
>>>>
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