Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Kevin -
The "serious realignment procedure" is an urban myth... I discussed
this with Bill Frost at Drake, and he said the techs used the procedure
in the manual.
Just about all alignment "problems" are the result of someone "fixing"
the transmitter! :-) Hopefully he didn't find it necessary to
"adjust" the height of the slugs in the RF Tune rack. That's about the
only place I've found that you can really mess one up.
Anyway, if you follow the manual procedure, it will come in fine unless
there is a bad cap somewhere. Just about all the trimmers have a fixed
cap across them, but VERY rarely have I seen one of those fail, barring
mechanical damage.
Get the Carrier Oscillator on frequency, make sure the Premixer LO
output is the DIFFERENCE of the Band Oscillator frequency and the PTO,
and that the output of the Mixer is at the right frequency, and you
should be fine. You might have to "nudge" the RF Tune a little to get
the trimmers in range on 10M. You should get a peak, and be sure that
it falls off a little before the adjuster screw falls out of the
trimmer!! Those trimmers are right at the minimum. For that reason, I
always put a little dab of clear nail polish on them. There's so little
spring tension left that if you don't, they'll shift the first time the
transmitter is bumped or the bandswitch is changed! All of a sudden
the 10M output is down.....
Speaking of adjuster screws, check R26 (680 - 1/2 W) by the shield
between the driver and final area under the chassis for value and
condition. This is the resistor that gets fried when someone adjusts
the trimmers with a metal screwdriver and shorts them to the chassis,
even momentarily.
Also, while you're in there, check the meter shunt resistor R36 (2.7 -
1/2W) on the small board just behind the three power resistors. If it's
off much, you can be setting the Final bias current to something other
than 100 mA, which is not good. If it has to be replaced, you'll have
to re-select R38 (~220 - 1/2W) located on the meter switch to set the
meter to read 100 mA, confirming by measuring the drop across R36 with a
DMM. Check R30, 31, 32 & 33 also. They should be within 5%.
Next, replace _at least_ the filter caps on the Bias supply in the
AC-4, or preferably, put in the excellent AC-4R board from Mike Bryce.
<http://www.theheathkitshop.com/drakeac4rreplace.html>
If the sidetone is audible with the key up, replace C129 (60 uF, 200VDC).
That done, it should be good for another 40 years!
73, Garey - K4OAH
Atlanta
Drake B & C-Line Service CDs
<http://www.k4oah.com>
Kevin LaHaie wrote:
Kevin LaHaie <[EMAIL PROTECTED]> made an utterance to the
drakelist gang
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Hi. Hope this didn't get duplicated, I am having some trouble posting
to the list?
I am reviving a T-4XB for a friend. It would not load up on any band,
and after careful (exhaustive!) review of all sections, it appears it
is just severly out of alignment. I did get 1 band in fair alignment
by 'hunting and pecking', but that could take a lifetime, not to
mention a few sets of finals!
The manual makes reference to a procedure for serious realignment that
could be obtained on request from customer service, and I am wondering
if that is available either on the web or someone has it that could
share it.
Any help in getting the T-4XB aligned appreciated, I have a signal
generator, scope, frequency counter, VTVM and DMM to work with.
AND, like it needs mentioning, if your friends are having problems,
try to keep them from 'fiddling' with the trimmers if you can help
it! My friend admits he played with all of them!
73 and thanks in advance to a great list!
-Kevin K7ZS
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