[Johnson] Valiant I crystal oscillator won't unkey

[Rodger]

Paul,

While you are in there I would make the keying modification since you do 
have crystals, it probably won't cure your current problem but it does 
improve the keying note with some crystals.

Your analysis of V11 operation is correct and if you haven't already 
replaced V11 try that first since it is easiest.  The other thing to 
definitely do if you have not done so already is replace the filter caps 
for the bias supply (C93A and C93B) as a reduction in bias voltage can 
cause this and if these caps go bad it can cause a great deal of 
additional damage.  If you do have to replace the bias caps you will 
need to check the modulator current and also the clamp tube setting.  If 
V11 and the bias caps are good then the most likely problem is R42 
and/or R41 drifting up in value.

While you are in there, check the filament leads from the LV transformer 
to the 866A rectifiers.  Early Valiants used regular hookup wire which 
isn't sufficient for the plate voltage that also appears on these 
wires.  If the arc and short to chassis it also will take out the LV 
transformer.  You have probably also replaced the suspect dropping 
resistor in the VFO that cooks the VR tube; if not it can be replaced 
through the left side of the VFO housing (your left facing from the 
front) without taking the entire VFO apart.

73, Rodger WQ9E

Paul Carreiro, N6EV wrote:
> Greetings..
> I want to confirm something before I go digging into the Valiant.  The 
> crystal oscillator (C1/C2 switch position) doesn't unkey when the key 
> is not closed.  The oscillator can be heard in the receiver, making 
> use of the crystal positions nearly impossible.  I just want to 
> confirm this indeed is anomalous.  The VFO fully unkeys with key-up.
>
> In the Osc meter position, the crystal osc has a resting current of 
> 12mA and a key down current of 14mA.  The VFO has 8mA resting and 22mA 
> key down osc current.
>
> In the buffer meter position, the crystal has a resting current of 4mA 
> and a key down current of 24mA (drive adjusted).  The VFO with the 
> same drive level has a resting buffer current at 0mA and a key down 
> current of 24mA.  So, another indication that the crystal osc is hung 
> semi-on in key-up condition.
>
> I've also confirmed that the R39 VFO keyer adjustment is operational 
> and correct.  This adjustment appears to only affect the VFO (left 
> half of V11)
>
> Looking at the circuit, am I correct in saying that the right half of 
> V11 (12AU7) controls the keying of the crystal oscillator?  It appears 
> to drive the pin 9 grid of V3 (6CL6) crystal oscillator / buffer.  Key 
> down does affect the crystal oscillator, as I'm getting an increase in 
> osc and buffer current in that condition.  But key up is not 
> completely unkeying the crystal, but works fine in VFO.  I'm 
> suspecting something on the right half of V3 to pin 9 of V3 is a miss.
>
> Another tid-bit.. looking at Valiant Information Bulletin #1, there is 
> a component change / addition to improve crystal oscillator keying.  
> R11 changes from 33k to 100k and the addition of two 1-Megohm 
> resistors on SW2.  This rig does not have that modification done.   
> Would that help?  Is it worth making this mod regardless?
>
> All tubes check good.
>
> Any advice welcome.  Anyone seen this before?
>
> Thanks and 73
> Paul  N6EV
>
> Johnson mailing list
> Home: http://mailman.qth.net/mailman/listinfo/johnson
> Help: http://mailman.qth.net/mmfaq.html
> Post: mailto:Johnson at mailman.qth.net
>
>