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Heathkit SB-401 relay RL1

Aug 7th 2012, 22:09


Joined: Sep 24th 2010, 13:12
Total Topics: 0
Total Posts: 0
I'm thinking of following a Heathkit recommendation to connect contact 7 of RL1 to ground to eliminate the problem of the transmitter remaining on transmit when I end transmission. This is due to "gassy" final tubes, the Heathkit bulletin states.

Maybe I'm missing something, but going through the schematics, I come up with six poles for RL1, not five. I do see a contact lug on the RL1 on my SB-401 without any connection. Can I assume this is number 7? Don't know if there are any other contacts without a connection. This could be possible.

Wonder if anyone has the connection diagram for RL1, or did the suggested fix.

Thanks all.

73's KC2ZDT

Aug 9th 2012, 19:02


Super Moderator

Joined: Apr 4th 1998, 00:00
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The Service Bulletin says to connect lug 7, not contact 7. It also says that this change was added to the instruction manual--it is quite likely that the modification has already been made. No, I wouldn't make the connection unless if I was absolutely sure as to what I was doing. You can easily make expensive mistakes and blow stuff up by mis-connecting tube wiring.

Zack Lau W1VT
ARRL Senior Lab Engineer

Aug 9th 2012, 23:55


Joined: Sep 24th 2010, 13:12
Total Topics: 0
Total Posts: 0
Thanks Zac for your reply.
Looking into this a bit further, there are two additional contacts (lugs) that are not connected. As you state, the mod may have been already made. So I am not going to attempt any changes unless I can come up ith the connection diagram for the relay. Also, it might not be possible without unsoldering a lot of the wires to this relay due to the high density of connections to it.



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