[Hallicrafters] HT-37 VOX Relay

[Mark K3MSB]

Well, good news.    Mostly…..



I measured the resistances on V15B-3 and they were pretty close with the
bandswitch in the STBY or MOX positions.  That indicated R51 and R52 were
OK.     Sometimes the resistance didn’t change, but would after cycling the
switch.     Unfortunately, the switch contacts are in the SSB subchassis
and I don’t feel like pulling it out.



I then removed the tube and, with the switch in the MOX position, grounded
V15-1.   The relay opened and closed nicely.



I then reinserted the tube.   The filament voltage on pin 6 was only 6 V,
and I remembered I had the transmitter powered up to only 115V off the
variac.   I upped it to 120V and the heater voltage was 6.3V.    Cycling
the function switch between MOX and STBY sometimes causes the relay to
close, sometimes not.    When not,  a slight “thump” on the relay will
close it.



I think those switches need a good cleaning.



Still looking into the OA2 issue…..


Mark K3MSB

On Mon, Mar 14, 2016 at 8:38 PM, Mark K3MSB <mark.k3msb at gmail.com> wrote:

> I’m working on an HT-37 transmitter donated to our radio club.
>
>
>
> The VOX Relay RY1 wants to close when I change the function switch from
> STBY to MOX and I can see it move, but it will not travel far enough to
> close the contacts.
>
>
>
> R69 Is OK, and I measured the RY1 coil resistance to be 9.5K.   The
> various voltage drops across R69 and the coil when the radio is in the MOX
> position show a current of 5 Ma.
>
>
>
> Specifically, the voltage drop across the 9.5K coil is 52V yielding 5 mA.
> I have no idea if these numbers are correct, but the current seem pretty
> small.
>
>
>
> The “Relay  Tube” V15B tested good, and I used a replacement with no
> difference in relay action.
>
>
>
> Measured voltages on VR15-1:  278/196,  and VR15-3  5.6/1.7   (STBY/MOX).
> There are in the ballpark.
>
>
>
> I tested all the tubes etc, played musical tubes a while,  cleaned the
> relay coil (bottom) with DeOxit,  adjust the screw adjustment on the coil
> bottom etc.  Nothing helped the relay to perform as expected.
>
>
>
> Also, the 0A2 VR tube will not light.   I tried 2 tubes (tested OK in a
> tester) and both show about 150V on pins 1 and 5 as expected.   With the
> OA2 removed, pin 5 is 187V.   It looks to be regulating, but I’d expect
> to see some glow.
>
>
>
> The bias measured at TP-2 is -49V.
>
>
>
> Comments welcomed; I’m concerned RY1 is bad.
>
>
> 73 Mark K3MSB
>