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Re: [Amps] How to Bypass TR circuitry in Alpha 86

Subject: Re: [Amps] How to Bypass TR circuitry in Alpha 86
From: Mark - N5OT <>
Date: Thu, 13 Feb 2020 07:32:26 -0600
List-post: <>
Hi Paul, nice to hear from you.  Yeah, I have followed that design modification philosophy about my amp, and used a lot of Alphas.  Interesting that QSK was such an end-all goal back in the days before using two radios at the same time, where, overnight, QSK became completely unnecessary.  I have not used QSK for many years.  Which as far as I can tell, renders the Alpha PIN diode design as a completely unnecessary risk when a relay would do fine like in the old days.  I don't mind hearing the sound of changing from receive to transmit and vice-vera. Something like that kerchunk makes me feel like I am not dead. Like blood still courses through my aging veins.

So not sure what to do.  It's a great AMP as far as taking my drive power and making it bigger.  That's all I really need it to do.  All the fancy full break-in stuff is unnecessary and it gripes me that it's what's stopping me from using what is otherwise a great AMP.  I would like to just side-step all of it and use the amp to amplify.  I no longer need to hear between code elements.

It seems like the kind of thing where you could clip a couple wires and put in a jumper and go back to making QSOs.  Easier still, just put it in permanent "transmit" mode since I have this fancy external TR switch.

It seems.  This amp is all-of-a-sudden way too fancy for me.

73 - Mark N5OT

On 2/13/2020 7:03 AM, Paul Christensen wrote:

You may have already seen this link that discusses replacement of the Alpha 
86's PIN T/R circuit with a pair of vacuum relays:

The Alpha 86 went through three evolutionary production changes and to the best of my 
knowledge, Alpha didn’t publish these changes in later owner's manuals.  
Ultimately, the fourth 86 iteration became the Alpha 89.

The primary change relates to the addition of high-voltage bias on the receive 
PIN diodes.  Late 86 models have extra PC boards.  This change, together with 
the pre-existing high-speed SWR protection circuit helped but did not eliminate 
all high SWR PIN failures.

In my opinion, Alpha didn't have a complete grasp on the protection problem 
until the late '90s when the last PIN circuit updates went into 87A and 89 
production.  Post Y2K 87A models seem to have very stable T/R circuits.

Paul, W9AC

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