[Amps] AL-80B questions

[Conrad G0RUZ]

Of course Rich it works very well, especially on this old chestnut! It
reminds me of the re-runs we have on BBC TV in the UK.

Still I must admit without you having a dig at Tom when he surfaces, I would
begin to worry. As I approach middle age, it's nice to know that some things
in life are dependable :-)

Conrad

-----Original Message-----
From: 2 [mailto:2 at vc.net]
Sent: 02 March 2003 17:36
To: conrad at g0ruz.net
Subject: RE: [Amps] AL-80B questions


Conrad -- Does your Delete button work?

>Here we go again (GROANNNNNNNNNNNNNNNN.............)
>
>Conrad G0RUZ
>
>-----Original Message-----
>From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
>Behalf Of 2
>Sent: 02 March 2003 12:30
>To: Tom Rauch; AMPS
>Subject: Re: [Amps] AL-80B questions
>
>
>
>
>>
>>>
>>> 1: Does this sound like a symptom of parasitic oscillations?
>>>   I thought the 3-500Z was pretty rugged with respect to faults.
>>
>>Parasitics, even assuming they would occur, can't cause tube failures
>unless
>>you see some solid evidence of excessive current on meters.
>>
>A jump to 250mA of ZSAC is not a clue?
>
>>I don't know what time period you are talking about, but I've had several
>>Amperex 3-500Z's fail in my own equipment. Amperex, like all foreign tube
>>companies, is a bit difficult to work with. My last conversations with
>>Amperex were only through Richardsons Electronics(who owns Amperex), and
>>involved 3-500Z grid-to-filament shorts.
>>
>>I had four 3-500Z tubes in a test fixture cycling only the filament
>>off-and-on once every minute, and within a day two tubes failed. In a week
>>they were all bad. All of them failed because the center of the filament
>>helice moved over and touched the grid.
>>
>>My conclusion is the repeated thermal cycling of the filament, and a
>>material or assembly flaw in the tube, caused the helice to move the few
>>thousands of an inch required to cause a short.
>>
>It takes more movement than this to short a 3-500Z.
>
>>> 2: Does anyone know of any problems with recently built Amperex bottles?
>>
>>Absolutely there are.
>>
>But Tom Rauch is apparently the only person on this planet who is
>convinced of this.
>
>>> 3: I'll probably help him install the parasitic supressor kit somethime
>>>this week.  Are there any other things to look for or suggested
>corrections
>>>to this thing that would make it less prone to eating another tube?
>>
>>Put a dead-chicken leg over the cabinet, and say a prayer instead. It will
>>be more effective.
>>
>The recognized amplifier expert plays the Ad Hominem Card.
>
>>Seriously, ask him how much often he cycles the amp on and off. Also be
>sure
>>voltages are set correctly on the power transformer taps, and that there
is
>>no error in filament voltage. Ameritron's transformer vendor, Schumacher,
>>moved to Mexico about a year or so ago and transformer quality was
suddenly
>>horrible. Bad connections were the least of the problems (it looked like
>>they soldered transformers with a hot rock), there were also some build
>>problems in transformers.
>
>Say what ?
>>
>>I'd assume Ameritron measured filament voltage at the tube, but they might
>>not have measured it correctly or with a good meter.
>
>So is Tom Rauch still employed by Martin F. Jue ?
>
>> The quality of
>>technical people is dropping like a rock as time passes. I'd re-measure
the
>>filament voltage, especially in light of the nature of tube failures.
>>
>Grid-fil shorts from too much filament V ?
>
>>Make sure your friend isn't needlessly cycling the filament off-and-on,
>>since the failures are on-and-off cycle related in tests I have done. I
>knew
>>a guy who ate 3CX1200D7's in a Henry like pop-corn because he cycled the
>>filament off and on about ten times a day. He'd get about two months on a
>>tube.
>>
>The 3cx1200D7 has no spec on fil inrush current.
>
>>Remember you are dealing with a white-hot filament
>
>1830 degrees K is hardly white hot.
>
>>that has one common
>>mechanical support point *at the very bottom*.
>
>There's a ceramic support  at the top of the filament.
>
>>The filament is about 2-3
>>inches long when wound in a tight helice, and is thousands of an inch from
>>the grid. Even if the tube is built properly, it isn't a good idea to
>>heat-cycle the filament needlessly.
>>
>>Ask him how often he turns it on and off BEFORE you tell him anything
else,
>>and see if it is abnormal. Also be sure he knows to keep operating grid
>>current below 125-150mA on carrier.
>>
>Eimac has no such advice in the specs.
>
>>73 Tom
>
>-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
>www.vcnet.com/measures.
>end
>
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-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
www.vcnet.com/measures.
end