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Re: [Amps] MKS brand 8877 test

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Subject: Re: [Amps] MKS brand 8877 test
From: "Paul Christensen" <>
Date: Mon, 30 Jan 2023 13:57:26 -0500
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>"There was a production issue related to Eimac and the two MRI equipment
makers who used the 8877."

Here's a chronological timeline from Dick Ehrhorn.  It's an interesting case
study and a horrid time period for ETO.  I know that the first 8877 QC
issues predate 1986:  

In 1979, I nearly lost my college job as a result of several failed 8877s,
purchased new from Richardson Electronics.  I don't know where Eimac's Ken
Atkinson is today, but he alone saved my job and my credibility with the
station owner. Ken sent a tested tube from the SLC plant and the transmitter
finally made licensed power.  

For those who expressed interest and/or skepticism about the issue, here's a
reasonably accurate time line of events from our QA records.

Eimac puts 8877 heat dam design change into production -- ~08/86 
        (Completely unknown to us at the time)

First identified tube failure at MRI end-customer field site   --   12/86

First suspect tube routed back to Eimac via ETO             --   01/87

Meeting with Eimac                                      --   05/87

FIrst fix devised by Eimac; second meeting w/Eimac      --   07/87

Third & fourth meeting with Eimac                       --   08/87

Initial Eimac delivery of "fixed" 8877's                        --   09/87

Delivery of "fixed" 8877's to customers                 --   10/87

Problem re-surfaces @ field customer(s)          --   03/88

FIfth meeting with Eimac                                  --   05/88

Second fix devised by Eimac                                     --   06/88

Initial Eimac delivery of 8877's with second "fix"               --   08/88

Delivery of "2nd fix" 8877's to MRI customers           --   09/88

Completion of field upgrade with replacement tubes      --   05/89

** NOTE: Because tube date codes approximate
        shipping rather than manufacture dates,
        they may vary ~1-3 months from the
        event dates given above.

Largest MRI RF amplifier manufacturer's record of 8877 usage by year:

            In new amps        As replacements
                             almost 100% due to
                             heat dam/g-k shorts

1987            500              575

1988            650             1600 

1989            500              550

Statistical data on average end of tube life in our MRI amps
(corrected from earlier off-hand estimates). Excludes small
"infant mortality" humps for both types @ 2400-2600 hrs.

        3CX800A7        18,500 hours (very sharp peak 
                        between 18,000 - 19,000 hours)

        3CPX5000A7      In excess of 30,000 hours. (Of 
                        course tube costs $2-3k in qty.) 

Dick  W0ID

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