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Fwd: [AMPS] 3-500Z amplifiers and grid current

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Subject: Fwd: [AMPS] 3-500Z amplifiers and grid current
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Subject: Re: [AMPS] 3-500Z amplifiers and grid current
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On Tue, 17 Mar 98 11:14:14 -0800 Rich Measures <> writes:
>>On Tue, 17 Mar 98 03:18:37 -0800 Rich Measures <> 
>>The welds caused infant mortality. 
>I have seen weld failures in Eimac tubes that were more than a year 
>of warranty.  

So? We all know that that era of Eimacs had problems..some failed before
others. Piss poor QA we all accept. 

>>The long term problem was real gas,
>>not the vanishing kind. I had several bad ones sent to me and they 
>>had that telltale glow...or worse. I was only able to recover one out 
>>maybe a dozen. 
>I rarely see a tube with bent filament helixes that exhibits gas 

You sound like Tom...what does that have to do with the single brand new
tube that you started this discussion with.  I sure hate drifty

>>>By what mechanism does an allegedly defective tube damage the 
>>>parasitic suppressor R and blow the grid choke?
>>A big bang in an amp without a HV surge resistor.
>A "big bang" undoubtedly involves some sort of positive hv arc to 
>ground.  The path to the chassis can not be through the grid because 
>grid is already connected to the chassis.  .  How can such an 
>possibly damage the VHF suppressor R, which is paralleled by typically 
>less than 0.001 ohm of copper wire?  

I guess that your version of a failure path and mine differ a lot.  The
DC and the  RF enhanced gas paths do differ.  Something I learned as a 
kid....the path of least resistance....but at age 15 I thought that meant

>>Real proof would clinch it Rich. How about setting up a SB-220, 
>>etc with a spectrum analyzer and try to create the incident ?
>What is "real proof".  Tom Rauch suggested that I faked the 
>of the parasite-toasted bandswitches.  

Who cares what Rauch thinks? 
He may be right or wrong...his opinion is as meaningless as yours without

 OJ claimed that 34 photos of 
>wearing the Bruno Magli shoes were all faked, and that proved there 
>was a 
>massive conspiracy againt him because he was black.

That is anothers method of deflecting the issue...shame on you for doing
the same.

  .  .  A stock 
>sb220 has been tested.  The amplifier reportedly exhibited consistent 
>damped ringing at the anode resonance of c. 110MHz when driven with 
>speed dits. 

"Reportedly" dont mean squat.

 However, the 220 did not sustain a full blown event 
>the test.  Does the damped vhf-ringing magically go away when low 
>parasitic suppressors are installed?  Nope, but the peak amplitude 
>>Until that occurs I find it a real stretch to believe that a brand 
>new 9
>>year old amp and tubes would harbor a dreaded parasitic at turn-on. 
>- Perhaps it's not all that stretchy.    During Final Test, a 
>pair of tubes are typically plugged in whilst the frisky Eimac 
>remain safely tucked away in their factory-sealed boxes.  .  Should 
>expect that tired old tubes have as much gain as new tubes? .  .  

Maybe in your version of reality.  In the real world amps are final
tested AND shipped with the same tubes.  Of course this does not include
kits. Early testing or QA rejects may use shop tubes...cuts down the cost
when debugging. 
Amp Supply thru brand Z amps included the serial ## of the tubes along
with Tune and Load readings into their 50 Ohm loads. This was an aid to
new users ( that could read)   of the initial setup parameters. 

.  I 
>have a tube that was mfg. in 1967, which still works, upon which I 
>confidently wager a large pizza with 4 toppings and salad bar, that it 
>won't oscillate.  .  

A tube....6L6 or what??  I have been thru scores of 3-500Z amps that seem
to run forever with the original 196x-7x era tubes. It is the later Eimac
years that fuel the fire....

Ciao  Carl  KM1H

>R. L. Measures, 805-386-3734, AG6K   
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