Hallicrafters HA-1 TO Keyer

Garey Barrell k4oah at MINDSPRING.COM
Fri Sep 18 09:08:31 EDT 1998

Hi Al -

The 5963 is a 12AU7 modified to minimize the "cathode interface" problem.

This has been discussed here  before, but essentially is a degradation of
tube performance caused by the tube remaining "cut-off" for long periods of

A new 12AU7 will work just fine in place of the 5963 in any position of the

The most common problem with the HA-1 is capacitor leakage.  The circuits
are very high impedance, (look at the values of the resistors in the timing
circuits,) so it doesn't take much leakage to upset things.

Only logical way to attack these problems is to replace all the paper caps
with modern film caps and all timing resistors with modern film types.  Any
other procedure is just chasing your tail.

By the way, I am not one who normally recommends "shotgunning" a vintage
piece of equipment.  Experience has shown me that it is just the only way
to effectively deal with this GREAT keyer.

73, Garey - K4OAH

At 11:37 PM 9/17/98 -0400, you wrote:
>A friend once called this kind of problem "FIB" for "Foot In Bucket".
>Remember the cartoons where a character steps in a paint bucket and
>limps around chasing his nemesis?
>I am having difficulty after cleaning up a TO Keyer.  Prior to cleaning
>the chassis I removed the tubes.  There were 4 12AU7s and two voltage
>regulators.  I failed to notice that the manual said three of the four
>should be 5963s and consequently didn't pay any attention to which
>sockets I got the 12AU7s from.  A 12AU7 is a 12AU7, right?  When I put
>it back together, it didn't work right.  I checked the tubes and found
>one bad, but the reason it was bad was that a pin was broken and came
>off when I removed it from the tester.  I had another 12AU7 (which also
>checked good) so I put it in.  The keyer comes the closest to working
>with only one of the four tubes in the V3 posistion, the divide by two
>flip-flop.  With all other tubes it is only possible to get dots, faster
>dots (the flip-flop is oscillating) or a continuous dash (but not
>self-completing dashes) by adjusting the balance of the flip-flop as
>specified in the manual.  With one of the 12AU7s in the V3 position it
>almost works, but often the first character sent when the dash paddle is
>pressed is a dot.  If the paddle is held down, the subsequent characters
>are dashes.  In some settings, the number of dashes is limited, i.e. the
>keyer starts sending a continuous dash.
>My questions are:
>1.  Anybody had this problem before with a TO Keyer?  If so, how did you
>fix it?
>2.  What is the difference between a 5963 and a 12AU7?  Why would
>Hallicrafters specify 5963 for 3 of the 4 12AU7s in the keyer?
>Thanks for any assistance any of you might be able to render to get my
>foot out of this bucket.
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