[Hallicrafters] Hallicrafters Digest, Vol 60, Issue 15

[Jim Liles]

Good morning Don:
The resistance chart is incorrect for V19-P1 --- it has a 234K resistor in 
line.  When using the VOX to control CW break in the first keystroke needs a 
moment to pick the VOX relay and engage the drivers.  If your first 
character begins with a dot, you will be disappointed.  Kindest regards Jim 
K9AXN


> Message: 1
> Date: Thu, 15 Jan 2009 14:23:46 -0500 (EST)
> From: Don VE3HUR <dstalk at execulink.com>
> Subject: [Hallicrafters] SR-400A VOX problems
> To: hallicrafters at mailman.qth.net
> Message-ID: <m1LNXoh-00HXAZC at smp>
> Content-Type: text/plain; charset=us-ascii
>
> The VOX on my SR-400A clips off the first dit of a CW character. It's
> not a sharp clipping but, rather, a slow dit/dah seems to fade in.
>
> The sidetone sounds ok and there is 12V P-P at the junction of R143 and
> R144 so I presume that the sidetone generator is ok.
>
> As per the manual, I measured the resistances around V19 and V20 and all
> were ok except for V19 pin 1 measuring 242K (should be 130K) and V20
> pin 2 measuring 3.9M/10.1M (should be 3M/7M).
>
> Voltage measurements on V20 were within tolerance. However, on V19 pin 1
> was only 81 volts (should be 135). Pin 7 was -106 volts (should be -130)
> but since that is to cut off V19A it should be ok. All voltages are for
> CW operation. The +230V line is ok and the bias line is -135V.
>
> I checked the resistors around V19 and V20 by measuring them in circuit
> and they all measured within tolerance except for R159 which tested ok
> when removed from the circuit.
>
> For test purposes I've disconnected the anti-trip by disconnecting R157.
>
> The two times I operated SSB I was told my audio was ok. I used an
> old Turner desk microphone and didn't have gain problems.
>
> Does anyone have any suggestions about why V19 pin 1's voltage and
> resistance are so far off. Also - any suggestions about diagnosing the
> VOX problem?
>
> 73, Don VE3HUR