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My first bet would be on the 300A's preamp relay, especially if it's one of the square white plastic "R50-E2-Y2" relays. They are a failure waiting to happen.

Second bet would be on the 300A's antenna relay. If yours has the three identical relays on a plug-in circuit board behind the Load control, you'll find it a challenge to obtain replacements. The "R10-E3604" relay is a custom version with a RF shield inside it next to the relay's coil. The pin pattern is different from the stock relay this size, so you end up drilling holes in the pc board and/or wire-jumpering foil traces to use readily-available replacement relays.

Good news is that if it's the other version, with the relays on the deck BELOW the Load control, you can simply bypass the preamp relay with a single wire jumper once you remove it from the pc board. The antenna relay on this one is in a socket. Far less effort to swap out.

Has it ever done this nasty trick with the amplifier taken out of line?

If so, that points to a fault in the radio, not the amplifier.

OR, there may be a separate fault in each one. Not such a far-fetched idea for a 40 year-old amplifier and radio.

73

<blockquote data-quote="nomadradio" data-source="post: 594546" data-attributes="member: 22">My first bet would be on the 300A&#039;s preamp relay, especially if it&#039;s one of the square white plastic &quot;R50-E2-Y2&quot; relays. They are a failure waiting to happen. Second bet would be on the 300A&#039;s antenna relay. If yours has the three identical relays on a plug-in circuit board behind the Load control, you&#039;ll find it a challenge to obtain replacements. The &quot;R10-E3604&quot; relay is a custom version with a RF shield inside it next to the relay&#039;s coil. The pin pattern is different from the stock relay this size, so you end up drilling holes in the pc board and/or wire-jumpering foil traces to use readily-available replacement relays. Good news is that if it&#039;s the other version, with the relays on the deck BELOW the Load control, you can simply bypass the preamp relay with a single wire jumper once you remove it from the pc board. The antenna relay on this one is in a socket. Far less effort to swap out.Has it ever done this nasty trick with the amplifier taken out of line? If so, that points to a fault in the radio, not the amplifier. OR, there may be a separate fault in each one. Not such a far-fetched idea for a 40 year-old amplifier and radio. 73</blockquote>

[QUOTE="nomadradio, post: 594546, member: 22"] My first bet would be on the 300A's preamp relay, especially if it's one of the square white plastic "R50-E2-Y2" relays. They are a failure waiting to happen. Second bet would be on the 300A's antenna relay. If yours has the three identical relays on a plug-in circuit board behind the Load control, you'll find it a challenge to obtain replacements. The "R10-E3604" relay is a custom version with a RF shield inside it next to the relay's coil. The pin pattern is different from the stock relay this size, so you end up drilling holes in the pc board and/or wire-jumpering foil traces to use readily-available replacement relays. Good news is that if it's the other version, with the relays on the deck BELOW the Load control, you can simply bypass the preamp relay with a single wire jumper once you remove it from the pc board. The antenna relay on this one is in a socket. Far less effort to swap out. Has it ever done this nasty trick with the amplifier taken out of line? If so, that points to a fault in the radio, not the amplifier. OR, there may be a separate fault in each one. Not such a far-fetched idea for a 40 year-old amplifier and radio. 73 [/QUOTE]

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