Hallicrafters HA1 Keyer

[Garey Barrell]

Ron -

Have you tried plugging in phones?  The sidetone goes
through "bypass" contacts of this jack, and are subject to
corrosion.  Just plugging and unplugging usually clears this up.

Have you checked for leakage through the pot body or to
chassis?  An ohmmeter from Pin 7 of V-4B to chassis should
read 0 - 2 Megohms as you rotate the shaft.

The circuit works by R27 charging C8 until it reaches approx
65V, at which point the neon bulb "fires" and shorts C8 to
ground.  This generates a negative pulse that cuts off V4B
momentarily, generating a pulse across the primary of
transformer T2 that "rings" and generates a weird looking
pulse that is coupled to the speaker.  The "frequency" heard
is a combination of the R27/C8 time constant, the
transformer and C14.

Check the voltage across the NE-2 bulb.  If it never reaches
~65V, nothings going to happen.  R27 going up in value
and/or leakage through C8 are the two most common failures.
  V-4B should have 150V on the plate, 0 on the grid, and ~4V
on the cathode.  K1 pins 2 & 3 must connect to "key" the
output, which also goes through the Phones jack and through
pins 6 and 7 on the Control Outlet, which must be shorted by
a jumper.

Let us know what you find!

73, Garey - K4OAH
Atlanta


Rinkie & Ron Pollack wrote:

> I've had this nice keyer for at least 30 years, and I'm kind of embarrassed
> that I can't figger out this problem, even tho I'm not a technical type.
>
> Cannot get the sidetone to work.  Here's what I've done:
>
> Checked that the jumper is in place on the accessory socket.
>
> Replaced the tube (V4)
>
> Replaced the NE2 bulb
>
> Replaced C8 and C9
>
> Checked tube voltages
>
> Checked speaker
>
> Checked resistances of resistors and pot.
>
> Checked the relay.  (Am using the relay contacts meant for the sidetone to
> key a Heathkit code practice osc for temporary sidetone!)
>
> Still no sidetone!   It appears that the oscillator runs continuously and
> the output of the transformer is keyed by the relay.  I assume that the
> transformer is ok, since if the primary were open then there would be no
> voltage on the plate, and I checked continuity on the secondary.
>
> Should the NE2 bulb be lit all the time ( It is not).  Is there any way to
> check the bulb itself?
>
> With fewer than a dozen parts in this circuit, it should be a cinch!  What
> am I missing?
>
> Also, occasionally the keyer will give just dots in either the dot or dash
> position, but it goes away quickly.
>
> I have used the keyer on and off for many years, but with a  SB401/303 combo
> that has a built in sidetone, so I turned the volume down on the keyer, but
> I seem to remember it not working years ago, but I never bothered to check
> it out because I wasn't using it.
>
> Any ideas on either of these problems?
>
> Thanks!
>
> Ron K2RP
>
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