"Bill Carpenter" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Well, the pot seems to be fine with the voltage moving smoothly from 0 to 1
volt as it should. I'm still seeing the sudden jump from 0 to full power in
CW mode only. In tune mode it operates properly.
Now what?
----- Original Message -----
From: "Garey Barrell" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Saturday, January 19, 2008 12:00 PM
Subject: Re: [drakelist] T4-XB problem
Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist
gang
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Bill -
I think the only source for a replacement today would be a junker. The AC
switches are still available from John Kriner, but I doubt if the pots
are. It is just a dual 500k pot, and that's one style that is at least
still available. I honestly don't know if both sections are audio (log)
taper or not. I kinda think they are.
The idea for the alignment is to just detune the "other" side of the
transformer while you tune "this" side. So hanging a clip lead would work
just as well. They DO have +250 VDC on them! Be sure and keep the plate
current low, as if it's too high it makes the peak hard to see.
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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Thanks Gary, I'll take a look at R79. If it's bad is there a replacement
available? Also while I have the cover off I want to run through an
alignment. Is there a better way then the procedure in the manual which
has you use a screwdriver to detune the rig? If not would attaching a
clip-on test lead work as well as a screwdriver? I can just see myself
accidentally grounding something and causing all kinds of smoke and
flame.
----- Original Message ----- From: "Garey Barrell" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Saturday, January 19, 2008 10:04 AM
Subject: Re: [drakelist] T4-XB problem
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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