[Drake] T4X sticking relay

Fri, 4 Jul 2003 10:52:08 -0400

The coil in my T4XC relay went open some years but I have never been able to
find a replacement.  It had a 15k ohm coil.  Had to replace it with a unit
with somewhere around a 2500 ohm coil and it has since never been reliable
with pull in and drop out.  I believe this is due to the higher current it
draws through the triode switching circuit.  6EV7 maybe if I recall?

73,
Rick, W2RW

----- Original Message -----
From: "Barry L. Ornitz" <[email protected]>
To: <[email protected]>
Cc: <[email protected]>
Sent: Thursday, July 03, 2003 9:25 PM
Subject: Re: [Drake] T4X sticking relay

> Jim Barrie, WA8SDF, asked:
>
> > Need the group's advice. The relay in my very early model
> > T4X has started to stick... after transmitting, I have to
> > hit the PTT switch a couple of times to get my R4C  back on.
> > I suspect the relay for the antenna isn't releasing...  I
> > can hear signals, but they are very weak until I cycle he
> > PTT switch, then I get full audio.
>
> You are correct that the problem lies with the relay.  This is
> a relatively common problem with high-impedance DC-coil relays
> like this.  One approach is to purchase a new relay.  I think
> Mouser stocks them.
>
> But in most cases, you can cure the problem by simply
> reversing the leads to the relay's coil.
>
> What happens is that over time the DC current magnetizes the
> relay's iron core, making it stick.  Naturally this does not
> happen with AC-coil relays.  If you have a very old,
> powerful,  tape-head demagnetizer, you can use this on the
> core.  However, since there is more than adequate "pull" from
> energizing the relay, reversing the leads will tend to
> magnetize the core in the opposite direction and let it work
> properly again.  In another 20 to 30 years, you may have to do
> this once again!    :-)
>
> Actually I first saw this problem with a friend's T-4x in
> 1972.  I have never seen this problem with my unit which I
> have had since early 1966, but then again I am not too active
> in using the radio.
>
>         73, Dr. Barry L. Ornitz     WA4VZQ     [email protected]
>
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