Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Bill -
The CW Gain is a separate section on the GAIN control, R79, along with
R76, 77 and 80 form an adjustable DC voltage divider from the +150V
regulated supply. The resultant voltage is applied to the balanced
modulator to unbalance it and allow the Carrier Oscillator signal to
pass through. The frequency of the Carrier Oscillator is also shifted
by ~ 900 Hz to allow it to pass through the LSB filter.
What you are describing sounds like an open R79 resistance element.
It's possible that it's just a bit of crud on the element so a shot of
Caig MCL CaiLube or other control cleaner might clear it.
You can measure the control voltage at the center conductor of the
shielded wire going to T14, just in front of the VOX Delay pot. It
should start at 0 and come up as you increase the GAIN control (in CW
MODE only) to about 1 VDC. There are two forward biased Ge point
contact diodes in series to ground from that point, which will limit the
voltage, although the current will continue to increase as you turn up
the GAIN control. I'd guess you are going to see 0 V at minimum GAIN,
jumping to ~1V when you get to ~9 o'clock on the control. But I've
been wrong before! :-)
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Bill Carpenter wrote:
"Bill Carpenter" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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I installed the AC4R upgrade in my AC4 this week which is a very nice
kit. The T4-XB seems to love it and was working extremely well. I
spent a couple of hours on 160 SSB last night and made a few CW
contacts with no problems on other bands. This morning when I was
tuning the transmitter on 80 I noticed that in CW mode that the gain
control suddenly had no effect on power out. It goes from no power to
full power as the control is advanced at about 9 o'clock very
suddenly. There is no gradual increase as there should be. In tune
and SSB mode it still works fine with the normal gradual increase.
Any ideas on how to begin trouble shooting this? I don't see any
obvious burned components - at least not yet. I'm hoping it's a tube
and not some hard to find component!
73,
Bill NZ0T
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