[Johnson] Valiant I crystal oscillator won't unkey
Paul Carreiro, N6EV
N6EV at MonteCarloSS.com
Tue Dec 16 00:47:00 EST 2008
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
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