One of the known causes of TX pin diode failure is arcing of L1 on the TR
board. In older models, the rubber insulating pad under the coil
disintegrates over time, allowing exposed parts of the wire to arc to the
board and a nearby screw. The surge can damage one or both TX PIN diodes.
In my case, most of the evidence of arcing was hidden under the coil and I
didn't notice the carbon arcing on the nearby screw. I removed L1, cleaned
up the board, replaced the pad with a more robust insulator, rewound the
choke and reinstalled it -- all without removing the TR board.
It's not hard to access L1 -- just unplug the amp, remove the top cover and
remove the cover to the TR compartment in the back of the amp. Well worth
some time to inspect L1 and the insulating pad.
73, Dick WC1M
-----Original Message-----
From: Jerry O. Stern [mailto:jsternmd@att.net]
Sent: Wednesday, March 1, 2017 10:55 AM
To: jim@audiosystemsgroup.com; 'Amps Amps' <amps@contesting.com>
Subject: Re: [Amps] Alpha Switching Diodes
I never heard of any official alteration to the pin diodes such as replacing
them with vacuum switches by Alpha in any of their last 3 (4?) company
manifestations. I know there have been people who have made the changes
themselves. As for the TX pin diodes (UM4006D or equiv), these rarely fail
and now with the cost pretty reasonable, if you have to replace them, they
will last another 20 years.
73
Jerry NY2KW
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Jim Brown
Sent: Wednesday, March 01, 2017 3:54 AM
To: Amps Amps
Subject: [Amps] Alpha Switching Diodes
I've heard that Alpha came up with a fix for problems with their switching
diodes on the 87A and 89 amps. I just bought one of each. Can anyone shed
light on this?
73, Jim K9YC
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