[ETO_Alpha] Pin Diodes

Wed, 6 Mar 2002 12:18:12 -0700

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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