[AMPS] SB-220 problem

[km1h @ juno.com]

On Sat, 6 Sep 1997 10:37:12 +0000 w8jitom@postoffice.worldnet.att.net
writes:
>I Wrote:
>
>> >The last thing you want, if the tube faults, is to have the grid 
>fly 
>> >up to 3000 volts.
>> >If the grid, because of series resistance, reaches anode voltage 
>> >levels during a fault... the next stop for the arc is the filament 
>> >and everything connected to the filament including the exciter. 
>
>Carl replied:
> 
>> I have never heard of that happening in any 3-500Z amp that uses 
>grid
>> chokes!  Your comment may be technically correct but a real stretch 
>IMO.
>
>You are entitled to your opinions, but experience has shown 
>otherwise.

Tom, you stick to your version and I will simply stick to my minuscule
35+ years experience in the trenches. Obviously we have differing
definitions of experience.


>> Maybe we should ask Rich what the Grid- Filament breakdown voltage
>> is.....preferably with a non bent filament. 
>
>Carl, think before you assume something needs to "arc".
>
>1.) The cathode is emitting electrons, the grid is suddenly rapidly 
>slammed to the positive rail. When the grid is at 3000 volts, the 
>emission currents alone will be at the saturation point of the 
>filament, up around a dozen amperes.
>
>
>2.) The tube, if it faults, most likely has some gas (unless the 
>anode welds broke, and the anode hit the grid). The dc test voltage 
>of a "cold good tube" NOT under a fault condition has almost NOTHING 
>to do with the breakdown voltage during an arc.
>
>Finally, the reason a 220 has less problems with arcing than higher 
>power amps is the HV power supply in the 220 is LESS than AL-80B 
>standards. It was a 600 watt CW output design, NOT a 1500 watt output 

More HorseCrap. The SB220 is a 2000W PEP input amp. The CW position was
simply to placate the FCC. In 1979 the rules were changed.  In the SSB
position the SB-220 will run ~ 1200W out on CW in all but the most
demanding criteria. The 220 may be a toy in your opinion but it is (was)
the best selling 2x 3-500Z amp of all time. 
Please be sure to let us all know when the AL-82 reaches that status. 




>> If your statement were true Tom, then the thousands of Heath, 
>Kenwood,
>> Drake amp owners have lost thousands of rigs and kept silent about
>> it.......
>
>I'm not sure about "thousands" Carl, but I know for a fact they have 
>lost "dozens".  Usually the damage is small, confined to a protection 
>diode or solid state device at the receivers input. In rare cases, 
>the damage is more severe.


Strange that I don't hear those numbers....maybe I don't "feel their
pain". 



>Carl, I respect you hands on experience but remember this. NO ONE 
>gets as much feedback about field failures as the manufacturer 
>does. Radio Kit is a very small fish in big pond. You have no idea 
>what field problems really are, because you see and hear only a tiny 
>tiny bit of what really goes on.

Gee, I guess my years as Service Manager at National Radio dont count??
Who do you think fielded the 8122 disaster? It wasnt Slick Willy!

Tom. I have spent most of my life in the Service side of life. It makes
no difference if it is ham amps or lawnmowers. Dealing with an upset
customer requires patience and understanding.
Go ahead and knock my little operation but tell me when was the last time
an Ameritron or MFJ customer could talk to you directly or immediately???


>
>When you become one of the largest end users of 3-500Z tubes, or 
>start ordering 811A's at a rate approaching 1000 tubes per month, and 
>sell 200 or more new amplifiers a month your data stream takes on a 
>whole new level of accuracy.

Well I will grant you and Ameritron/MFJ the King of 811A's (well behind
Collins) but as far as 3-500Z's you are still playing catch up. I say
that in comparison with Heath, Drake and  any other 3rd you care to
add.....Amp Supply, Henry, KW, Ten-Tec, QRO, Swan, etc. ....take ur best
shot. Ameritron is not even close to being a 3-500 leader...yet. Wannabe
yes....leader  no.


 If you ignore any problems, you 
>simply go out of business (or sometimes in and out).

A simple fact as exemplified by the past and present players in the amp
business.


>I doubt YOU, despite running a successful customer driven profitable 
>small business, can pull up a data base and track the service history 
>of two thousand new amplifiers a year, or look at the percentage of 
>returns on thousands of tubes in a year.


Of course I cant, but I and many others can track problems across product
lines that "house engineers" either refuse to admidt or are too hung up
in their own importance to get away from the water cooler to investigate.
Just read DILBERT a few times to determine your own level in the
structure.

73....Carl   KM1H


BTW, to anyone that is still awake enough to read this far....excuse the
sometimes scattered answers. I typed this over about 6 hours and am now
too tired to proofread. 





>73, Tom W8JI

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