Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Andy -
Great! Sorry I didn't mention the C140 part. I really wasn't up to
the "replacement" point yet. You jumped ahead! :-)
Your symptoms plus the keying adjustment improvement indicates that the
problem was most likely the bias cap in the AC-3. Good to replace it
though, since that's the one electrolytic that can destroy finals, power
supply and/or transmitter if it fails, even if just in standby. The
rest are probably not far behind either, so cheap insurance. If that
blue cap bothers you as much as it does me, you might want to take a
look at:
<http://www.wb4hfn.com/DRAKE/DrakeArticles/TechTips/FilterCapacitorRebuilding.htm>
Frontier Electronics will do this for you for $35:
[EMAIL PROTECTED]
Anyway, it's fixed. That's Job 1.....!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Andrew Catanzaro wrote:
Garey,
I bought the AC-4 power supply replacement kit from the Heathkit Shop
and installed it in the AC-3. The burble on the CW note vanished.
Now I can tell with a local receiver that the note is great.
While I was at it, I replaced the electrolytics on the chassis of the
T-4XB. Only after I physically removed C129, did I realize the can
also contained C140. Found a 150 uF 450 volt cap that Crazy-Glued
into the opening left by removing the can and found a smaller
electrolytic to hang under it to replace C140, and looks like the CW
semi-QSK keying adjustments aren't so critical (VOX level and VOX
delay). (I know, a computer-grade blue plastic electrolytic's
appearance is anathema on the surface of that vintage copper chassis,
but hey, it works!)
Thanks for your help!
73,
Andy W9NJY
Milwaukee WI
----- Original Message ----- From: "Garey Barrell" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Sunday, July 29, 2007 11:43 AM
Subject: Re: [drakelist] Fine burble on T-4XB note
Garey Barrell <[EMAIL PROTECTED]> made an utterance to the
drakelist gang
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Andy -
Most likely power supply ripple. There are not many good caps left
in AC-3s after almost 50 years.
Since you are able to replicate the burble locally, you could try
bridging a good cap across the can cap in the T-4XB itself (C129),
and the output cap (C5b) of the bias supply in the AC-3 (watch
polarity!). Those are the two most likely troublemakers. If
neither of those affect the burble, you could try to bridge the
output cap of the LV supply (C4b).
If bridging the caps in the AC-3 resolves the problem, you might want
to consider the AC-4R from The Heathkit Shop. It replaces everything
except the transformer and bias pot.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Andrew Catanzaro wrote:
"Andrew Catanzaro" <[EMAIL PROTECTED]> made an utterance to the
drakelist gang
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I have recently gotten a Drake B-line operational and am very happy
with it. The R-4B is a fantastic receiver. I have built two Norcal
DDS VFO's to replace the PTO's and it's great having frequency
resolution to the last Hz and no drift.
A friend with good ears and who lives close by told me that there is
an irregularity on my CW note. People far away tell me my note is
fine. I took a separate receiver and used only a dummy load on the
transmitter and a dummy load on the receiver so it would not be
overloaded. I can hear the raspiness or burble. It's like a fine
modulation on an otherwise great CW note. Going back to the original
Drake PTO does not fix the problem. It sounds exactly the same. I
swapped out all the tubes for NOS, and there was no change. I am
using an AC-3 power supply with the original caps. There is nothing
that sounds like AC hum on the signal. Is this a normal observation
of the T-4XB's CW note or is there something wrong? Except for my
friend four miles away, and my own observations, all comments on the
Drake's signal have been unqualified positive remarks.
I listen to my K2's CW note in the same test receiver with the same
dummy loads and the K2's note is absolutely pure.
Any comments or suggestions greatly appreciated!
73,
Andy W9NJY
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