[ETO_Alpha] Pin Diodes

Mon, 18 Mar 2002 16:55:39 -0500

The 89 is about 1 1/2 years old. So far so good.

At 12:18 PM 03/06/2002 -0700, you wrote:
 >Jerry..I have an early Alpha 87A, circa '90.  I've never had a problem with
 >the amp.  I'm wondering the year of manufacture for your Amp--is it an ETO
 >amp or Crosslink?
 >
 >73//Ron K5MM
 >
 >----- Original Message -----
 >From: "Jerry Cudmore" <[email protected]>
 >To: <[email protected]>
 >Sent: Wednesday, March 06, 2002 9:15 AM
 >Subject: Re: [ETO_Alpha] Pin Diodes
 >
 >
 >> Hi all. I originated the post regarding the pin diodes and would like to
 >> follow up with more information. There is a voltage divider from the 2800
 >v
 >> source comprised of 4 sets of 470k film resistors. Two resistors in
 >> parallel equal about 240k. One set of these were open and the other was
 >> about 600k. When I first got the amp a couple of months ago I looked
 >inside
 >> to confirm the voltage taps on the transformer. At that time since this
 >was
 >> a recent purchase, I did a careful visual inspection. I did notice one of
 >> those film resistors had a burn mark. But the amp was working so I did not
 >> "fix it" as sometimes we tend to do. Last Saturday the same diodes that
 >> were replaced before had failed. When I called Alpha they sent me the
 >parts
 >> no charge under warranty. I was pleased with their assistance and believe
 >> customer satisfaction is a prime concern for them. The Alpha technicians
 >> admitted more 89 amps come in with this same pin diode problem that 87A's.
 >> The 89 and 87a use the exact same PA/RF/Power supply. So why do more 89's
 >> fail?.
 >>
 >> I would tend to think operator error. In my case I am very religious about
 >> tuning and always have used my tuner with just the exciter. The amp never
 >> saw more that 1.5 to 1 swr any time. I also never push it past the 1500
 >> watts. So I still have no explanation as to why the diodes fail. I now
 >have
 >> extras in case there is a next time. I also have never seen a fault
 >> condition on this amp because I never created a condition to cause it to
 >fault.
 >>
 >> Technical tip
 >>
 >> If the diodes open you will have no receive rf. If they short you will not
 >
 >> be able to get any power out since the soft fault will kick in because
 >> excessive current is drawn in relation to rf produced. Unfortunately there
 >> is no theory manual. I have learned quite a bit about the protection
 >> circuits, it is comprised of many op amps as comparators "watching"
 >> voltages currents, temperature. When it faults you never know what caused
 >> it to fail.
 >>
 >> Maybe by thinking about what precipated a pin diode failure in these amps
 >> we can come to logical conclusions.
 >>
 >> I would be interested in hearing from any users of 86,89, 87a owners who
 >> have had this type of failure.
 >>
 >> Thanks, 73's
 >>
 >> Jerry
 >>
 >>
 >>
 >>
 >>
 >>
 >>
 >> At 08:03 AM 3/6/02 -0500, you wrote:
 >>  >Hello to all Alpha users,
 >>  >    I seem to remember Alpha had a problem on the '86 with low bias
 >voltage
 >>  >on the pin diodes.  I would suggest, if you have problems on an '87A, to
 >>  >check and make sure the bias voltage is high enough.
 >>  >    As someone else said, the service fellow in the southeast should be
 >able
 >>  >to help you if you don't want to go to the new Alpha in Colorado
 >>  >    Good luck & 73,
 >>  >George        K8GG
 >>  >
 >>  >----- Original Message -----
 >>  >From: "Jerry" <[email protected]>
 >>  >To: <[email protected]>
 >>  >Sent: Sunday, March 03, 2002 1:14 PM
 >>  >Subject: [ETO_Alpha] Pin Diodes
 >>  >
 >>  >
 >>  >> Anyone know of a better part to replace the receive pin diode in the
 >87A,
 >>  >> 89 series amps. The part is a KS1001, the amp uses 4 of these. My 89
 >has
 >>  >> blown these twice this year. I never push it past legal.
 >>  >>
 >>  >> Thanks.
 >>  >>
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 >>  >>
 >>  >
 >>  >
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