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All:<br>
<br>
I do not apply full power to an old rig. It is not necessary and
can do a lot of damage. <br>
<br>
I like installing a 60 watt or 120 watt (120VAC) incandescent lamp
in series with the input power. This limits the 120VAC current to 1
or 2 amps and prevents a lot of smoke. <br>
It also allows one to take some measurements. I have been known to
short the load with a clip lead (the DX-60 in this case) when the
power is tuned on, then when the lamp is lit, I remove the load
short. In this way there is no surge to the load when the power is
applied to the load. The load sees a nice constant current 1 or 2
amps. <br>
<br>
I have also installed a switched AC outlet and an isolation
transformer, at my bench, which I use during these times. <br>
<br>
Something to think about. <br>
<br>
ALSO: <br>
Old rigs have aluminum electrolytic capacitors which need to be
slowly powered up (re polarized, I think is the term) as the leakage
current through the capacitors will be high when power is first
applied. A variable transformer will allow the power to be
increased slowly over a 10 hour or 24 hour period and this seems to
work. Again, I use a 60 watt or 120 watt (120VAC) incandescent lamp
in series with the input power which will limit the current if
something drastic happens during this process. <br>
<br>
If you are not qualified or experienced to work on this equipment
then do not. <br>
<br>
Later,<br>
Paul <br>
VE1AVD <br>
<div class="moz-forward-container"><br>
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<th nowrap="nowrap" valign="BASELINE" align="RIGHT">Subject:
</th>
<td>Re: [Heath] The DX-60B Issue</td>
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<tr>
<th nowrap="nowrap" valign="BASELINE" align="RIGHT">Date: </th>
<td>Sun, 01 Apr 2018 21:52:38 -0700</td>
</tr>
<tr>
<th nowrap="nowrap" valign="BASELINE" align="RIGHT">From: </th>
<td>Kenneth G. Gordon <a class="moz-txt-link-rfc2396E" href="mailto:kgordon2006@frontier.com"><kgordon2006@frontier.com></a></td>
</tr>
<tr>
<th nowrap="nowrap" valign="BASELINE" align="RIGHT">To: </th>
<td>Doug & Kathy Davies <a class="moz-txt-link-rfc2396E" href="mailto:dkdavies3@gmail.com"><dkdavies3@gmail.com></a></td>
</tr>
<tr>
<th nowrap="nowrap" valign="BASELINE" align="RIGHT">CC: </th>
<td><a class="moz-txt-link-abbreviated" href="mailto:Heath@puck.nether.net">Heath@puck.nether.net</a></td>
</tr>
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<br>
<div class="moz-cite-prefix">On 4/2/2018 11:52 AM, Kenneth G. Gordon
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:5AC1B716.31731.32886BA@kgordon2006.frontier.com">
<pre wrap="">On 31 Mar 2018 at 16:09, Doug & Kathy Davies wrote:
</pre>
<blockquote type="cite">
<pre wrap="">testing. When I plugged it in, all seemed ok i.e all the tube filaments lit up and nothing smoked.
Then, I put the Function Switch in TUNE and got a loud hum from the transformer and I let the
smoke out of resistor R35. I re-checked everything and found that resistor R34 was open.
</pre>
</blockquote>
<pre wrap="">
The loud hum from the power transformer indicates that your +HV is dead-shorted
somewhere. Either there was a wiring error or a component had failed or was installed
incorrectly.
For instance, if you had inadvertently connected C-39 and C-43 in revese, they would show
a dead short to ground.
</pre>
<blockquote type="cite">
<pre wrap="">Now I don't know if R34 was open prior to R35 burning up. I didn't check component values prior
to testing. The question then is, did R34 open as a result of R35 smoking or was it open prior to
that event?
</pre>
</blockquote>
<pre wrap="">
>From the sound of things, both burnt up at the same time. If R-34 was open, all that would
do is prevent the plate-voltage (~ 700 VDC) from reaching the final amp plate.
</pre>
<blockquote type="cite">
<pre wrap=""> I would think that if R34 was open prior to testing, it would certainly put a huge strain
on R35 causing it to burn out. Am I correct here?
</pre>
</blockquote>
<pre wrap="">
No. The two resistors are in separate parts of the circuit: if one failed, that would have zero
bearing on the other one.
</pre>
<blockquote type="cite">
<pre wrap=""> Going over the circuit, I can't see anything
else that would have caused R35 to smoke. Any ideas?
</pre>
</blockquote>
<pre wrap="">
You have a dead-short to ground at the 700 VDC output lead of your power supply.
Is C-19 shorted?
As another fellow mentioned, be EXTREMELY CAREFUL HERE: THAT VOLTAGE IS
LETHAL!!!!!
Ken W7EKB
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</pre>
</blockquote>
<br>
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