--------- Begin forwarded message ----------
From: km1h
To: w8jitom@postoffice.worldnet.att.net
Subject: Re: Bent filaments
To: <amps@contesting.com>
Date: Mon, 14 Jul 1997 17:08:53
Message-ID: <19970714.170645.9695.6.km1h@juno.com>
References: <19970714170655.AAB12845@fred>
On Mon, 14 Jul 1997 13:12:20 +0000 w8jitom@postoffice.worldnet.att.net
writes:
>> From: km1h@juno.com (km1h @ juno.com)
>> Subject: [AMPS] Re: Bent filaments
To: <amps@contesting.com>
>> Date: Mon, 14 Jul 97 13:54:44 +0000
>
>> At least the grid choke school of thought and possibly Rich's
>"network"
>> act as fuses and can often save the tube.
>
>No sale Carl.
>
>When the tube faults the grid flys right up to full anode voltage.
>The grid just as often as not arcs to the filament in that condition,
>wiping out all the stuff in the cathode return.
I see that you still enjoy selectively editing my original messages Tom.
As I said...I am really not sure of the true path of the "big bang".
I am also VERY comfortable with grid "fuses" while the snake oil salesmen
ply their wares. Note I used the plural.
"No Sale" is correct for now; I certainly wouldnt buy a car from either
one of you guys right now.
>
>Fusing the grid for HV arcs is dumb, because the grid to anode arc is
>generally in the harmless area of the very stout grid support
>or well reinforced grid cage rather than to the hotter and
>more magnetically susceptible filament structure.
That is the 2nd or 3rd time in a week you have referred to me as dumb,
not an engineer, etc. Sorry Old Bean but I can pretty much keep up with
any math and if I bog down, my EE son can help. Please save your insults
for Rich....
>
>The proper place to limit fault current is in the anode, near the
>filter caps, as you suggested. The last thing in the world anyone
>would want is a grid flying up to 3000 volts.
Thank you....but I fail to understand why B+ limiting is so much of a
secret or suprise to so many. Geez, where have some of these people been
for 20+ years??
>>offers no such protection which IMO is why the AL-82 (and similar
>> designs) often causes considerable damage when whatever it is does
>its
>> mischief.
>
>What do you call considerable damage? Ameritron uses an AL-82
>running at 4500 volts to check tubes for outgassing and arcs, and the
>ONLY components that get damaged in a fault are the zeners (on
>rare occasion) and the meter protection diode.
>
>Perhaps you can elaborate on the components you recall seeing
>damaged? How many AL-82's and 80 series PA do you see? Be honest, I
I am being honest Tom and I gave you this info months ago. We both know
that I cannot say for 100% sure what CAUSED the damage since I get the
amps well after the fact. Even if it is cockpit problems, the amps should
be designed to minimize the damage.
Anyway on the AL-82 it ALMOST always includes a tube, diode, plate choke
and bandswitch Or at least 3 out of the four. I probably have some bad
switches and chokes around in the "dead" box.
On the AL-80A/SB-1000 we have already been thru the bandswitch problem. I
see 2 distinct failures with these amps. Blown bandswitches, probably due
to cockpit error, and then blown tube and diode from the "X" factor. I
seldom see a bad switch AND tube at the same time in this series.
>depend on feedback like yours to learn.
>
>> I do know as fact, that any 220 that I have reworked with my own
>> parasitic suppressors, series B+ resistor and original grid circuit
>has
>> not lost a tube. Over the years that is a considerable number of
>amps.
>
>That sounds like a used car service center sales pitch Carl. The
>3-500Z Eimac tube had such a good service history, I don't see how you
>
>ever process enough amplifiers to get a good data base.
I would venture a guess that I see a lot more amps from ALL sources than
you do Tom. And there you go with the jabs again. Sorry I dont have a
MSEE on the wall, but I have never seen your credentials either....
>I doubt that thousands of 3-500Z's run through Radiokit's doors, and
>the failure rate of 3-500Z's is so low (other than the Chinese
>junk) it would take a very large data base to get any idea what the
>failure rate and effects of modifications really are.
My criteria is very simple....I count the returns and callbacks. If my
sampling is not enough for your scientific profile, I am sorry.
>Of course if CASH went in my pocket for selling mods, I might spend
>all my time saying I had a magic 100% reliable cure also, hi. ;-)
I dont sell stability mods for HF amps Tom, just a shade tree mechanic
that fixes the engineers mistakes.
>
>1.) The 3-500Z's number one problem since 1982 or so has been broken
>anode welds letting the anode cock and touch the grid. Over half of
>Ameritron's tube failure records indicate bad welds. When the anode
>falls off or is sitting at a large tilt, it's pretty easy to
>determine the failure's cause.
I saw a bunch of those when I WAS actively selling Eimac 3-500Z's. No
argument at all.
>
>2.) Outside of two definite production periods, one about four years
>ago when Eimac changed testing specs (which they changed back) and
>another when they made the last batch of tubes and the employees all
>knew they were on the way out, gas failures and related arcs were
>rare. All of the other failures combined, bad seals, grid filament
>shorts, broken glass, etc did not equal the weld problems.
Yep, open the box and look at the internals rattling around.
>Even though I have the utmost confidence you do the best job you can,
>I doubt a Radiokit modification could correct manufacturing defects
>in the tube welds.
Welds are not even an issue Tom, or is this just another smoke screen?
Any amp I see had ANY weld problems resolved ages ago.
>
>Either your data base was VERY small, or you discovered a way to
>repair welds in the tube.
Cut the crap please...as Ian said elsewhere "you are bloody well
irritating me". You ask for data and then slam it....have you ever
considered a job as Clintons Press Secreatry? They need a first class
BSer.
73....Carl KM1H
>73, Tom W8JI
>
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>
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