[Amps] How to Bypass TR circuitry in Alpha 86

[Paul Christensen]

Mark,

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:

http://volim63gtenet.mydomain.com/webservice3/old-mike/Mike/n3eaq_files/Alpha86/Alpha86.htm

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